一，应用程序创建
- 从AndroidManagerService开始，ActivityManagerService.StartProcessLocked
源码位置：http://androidxref.com/4.4.4_r1/xref/frameworks/base/services/java/com/android/server/am/ActivityManagerService.java
private final void startProcessLocked(ProcessRecord app, String hostingType, String hostingNameStr){
··· ···
try {
int uid = app.uid;
int[] gids = null;
int mountExternal = Zygote.MOUNT_EXTERNAL_NONE;
if (!app.isolated) {
int[] permGids = null;
try {
final PackageManager pm = mContext.getPackageManager();
permGids = pm.getPackageGids(app.info.packageName);
Process.ProcessStartResult startResult = Process.start("android.app.ActivityThread",
app.processName, uid, uid, gids, debugFlags, mountExternal, app.info.targetSdkVersion, app.info.seinfo, null);
··· ···
}
首先获取要创建的应用程序的进程uid和用户组gid，然后通过Process类静态成员函数start来创建应用程序进程。
- Process类，
Process.start
Process.startViaZygote
Process.zygote
源码位置：
http://androidxref.com/4.4.4_r1/xref/frameworks/base/core/java/android/os/Process.java
public static final ProcessStartResult start(final String processClass,
final String niceName,
int uid, int gid, int[] gids,
int debugFlags, int mountExternal,
int targetSdkVersion,
String seInfo,
String[] zygoteArgs) {
try {
return startViaZygote(processClass, niceName, uid, gid, gids,
debugFlags, mountExternal, targetSdkVersion, seInfo, zygoteArgs);
} catch (ZygoteStartFailedEx ex) {
Log.e(LOG_TAG,
"Starting VM process through Zygote failed");
throw new RuntimeException(
"Starting VM process through Zygote failed", ex);
}
}
private static ProcessStartResult startViaZygote(final String processClass,
final String niceName,
final int uid, final int gid,
final int[] gids,
int debugFlags, int mountExternal,
int targetSdkVersion,
String seInfo,
String[] extraArgs)
throws ZygoteStartFailedEx {
synchronized(Process.class) {
ArrayList argsForZygote = new ArrayList();
// --runtime-init, --setuid=, --setgid=,
// and --setgroups= must go first
argsForZygote.add("--runtime-init");
argsForZygote.add("--setuid=" + uid);
argsForZygote.add("--setgid=" + gid);
if ((debugFlags & Zygote.DEBUG_ENABLE_JNI_LOGGING) != 0) {
argsForZygote.add("--enable-jni-logging");
}
if ((debugFlags & Zygote.DEBUG_ENABLE_SAFEMODE) != 0) {
argsForZygote.add("--enable-safemode");
}
if ((debugFlags & Zygote.DEBUG_ENABLE_DEBUGGER) != 0) {
argsForZygote.add("--enable-debugger");
}
if ((debugFlags & Zygote.DEBUG_ENABLE_CHECKJNI) != 0) {
argsForZygote.add("--enable-checkjni");
}
if ((debugFlags & Zygote.DEBUG_ENABLE_ASSERT) != 0) {
argsForZygote.add("--enable-assert");
}
if (mountExternal == Zygote.MOUNT_EXTERNAL_MULTIUSER) {
argsForZygote.add("--mount-external-multiuser");
} else if (mountExternal == Zygote.MOUNT_EXTERNAL_MULTIUSER_ALL) {
argsForZygote.add("--mount-external-multiuser-all");
}
argsForZygote.add("--target-sdk-version=" + targetSdkVersion);
//TODO optionally enable debuger
//argsForZygote.add("--enable-debugger");
// --setgroups is a comma-separated list
if (gids != null && gids.length > 0) {
StringBuilder sb = new StringBuilder();
sb.append("--setgroups=");
int sz = gids.length;
for (int i = 0; i < sz; i++) {
if (i != 0) {
sb.append(',');
}
sb.append(gids[i]);
}
argsForZygote.add(sb.toString());
}
if (niceName != null) {
argsForZygote.add("--nice-name=" + niceName);
}
if (seInfo != null) {
argsForZygote.add("--seinfo=" + seInfo);
}
argsForZygote.add(processClass);
if (extraArgs != null) {
for (String arg : extraArgs) {
argsForZygote.add(arg);
}
}
return zygoteSendArgsAndGetResult(argsForZygote);
}
}
在《Android系统源代码情景分析》一书中用的是2.3的代码，里面的start函数包含supportsProcess来判断系统是否支持Binder进程通信机制，而在本文中使用的是4.4的代码，其中start函数已经删除了该部分，start函数直接调用startViaZygote函数，实际的start已经没有任何用处，至今保留是为了代码兼容。
startViaZygote首先将传入的参数添加到字符串列表argsForZygote中，然后调用zygoteSendArgsAndGetResult函数来请求Zygote进程创建一个新的应用程序进程。
private static ProcessStartResult zygoteSendArgsAndGetResult(ArrayList args)
throws ZygoteStartFailedEx {
openZygoteSocketIfNeeded();
try {
/**
* See com.android.internal.os.ZygoteInit.readArgumentList()
* Presently the wire format to the zygote process is:
* a) a count of arguments (argc, in essence)
* b) a number of newline-separated argument strings equal to count
*
* After the zygote process reads these it will write the pid of
* the child or -1 on failure, followed by boolean to
* indicate whether a wrapper process was used.
*/
sZygoteWriter.write(Integer.toString(args.size()));
sZygoteWriter.newLine();
int sz = args.size();
for (int i = 0; i < sz; i++) {
String arg = args.get(i);
if (arg.indexOf('\n') >= 0) {
throw new ZygoteStartFailedEx(
"embedded newlines not allowed");
}
sZygoteWriter.write(arg);
sZygoteWriter.newLine();
}
sZygoteWriter.flush();
// Should there be a timeout on this?
ProcessStartResult result = new ProcessStartResult();
result.pid = sZygoteInputStream.readInt();
if (result.pid < 0) {
throw new ZygoteStartFailedEx("fork() failed");
}
result.usingWrapper = sZygoteInputStream.readBoolean();
return result;
} catch (IOException ex) {
try {
if (sZygoteSocket != null) {
sZygoteSocket.close();
}
} catch (IOException ex2) {
// we're going to fail anyway
Log.e(LOG_TAG,"I/O exception on routine close", ex2);
}
sZygoteSocket = null;
throw new ZygoteStartFailedEx(ex);
}
}
首先通过openZygoteSocketIfNeeded()来创建一个LocalSocket对象,用来和Zygote进程通信，然后将传入的参数写道LocalSocket这个对象中，Zygote进程收到参数后就会创建新的应用进程，然后将Pid返回到result，然后这个pid就被返回到AMS（AndroidManagerService）中。
LocalSocket对象的创建过程如下：
private static void openZygoteSocketIfNeeded()
throws ZygoteStartFailedEx {
int retryCount;
if (sPreviousZygoteOpenFailed) {
/*
* If we've failed before, expect that we'll fail again and
* don't pause for retries.
*/
retryCount = 0;
} else {
retryCount = 10;
}
/*
* See bug #811181: Sometimes runtime can make it up before zygote.
* Really, we'd like to do something better to avoid this condition,
* but for now just wait a bit...
*/
for (int retry = 0; (sZygoteSocket == null) && (retry < (retryCount + 1)); retry++ ) {
if (retry > 0) {
try {
Log.i("Zygote", "Zygote not up yet, sleeping...");
Thread.sleep(ZYGOTE_RETRY_MILLIS);
} catch (InterruptedException ex) {
// should never happen
}
}
try {
sZygoteSocket = new LocalSocket();
sZygoteSocket.connect(new LocalSocketAddress(ZYGOTE_SOCKET, LocalSocketAddress.Namespace.RESERVED));
sZygoteInputStream = new DataInputStream(sZygoteSocket.getInputStream());
sZygoteWriter = new BufferedWriter(new OutputStreamWriter(sZygoteSocket.getOutputStream()), 256);
Log.i("Zygote", "Process: zygote socket opened");
sPreviousZygoteOpenFailed = false;
break;
} catch (IOException ex) {
if (sZygoteSocket != null) {
try {
sZygoteSocket.close();
} catch (IOException ex2) {
Log.e(LOG_TAG,"I/O exception on close after exception", ex2);
}
}
sZygoteSocket = null;
}
}
if (sZygoteSocket == null) {
sPreviousZygoteOpenFailed = true;
throw new ZygoteStartFailedEx("connect failed");
}
}
sZygoteSocket是Process类中的一个静态成员变量，首先new一个LocalSocket对象，保存在sZygoteSocket中，然后将之与ZYGOTE_SOCKET建立连接，ZYGOTE_SOCKET(Zygote进程运行后会创建一个名为zygote的Socket，这个Socket与设备文件/dev/socket/zygote绑定在一起，这个Socket的地址就是ZYGOTE_SOCKET)，连接过程就是sZygoteSocket在/dev/socket/文件夹下找到zygote文件，然后与之绑定的过程。
然后通过数据流的写入和输出完成了与Zygote进程的通信。
然后再来看下Zygote端：
上面说到，Zygote进程启动后会创建一个名为zygote的Socket，等待AMS与之通信，过程如下：
源码位置：
http://androidxref.com/4.4.4_r1/xref/frameworks/base/core/java/com/android/internal/os/ZygoteInit.java
在2.3的代码中名为runSelectLoopMode，在4.4的代码中名字改为了runSelectLoop，
private static void runSelectLoop() throws MethodAndArgsCaller {
ArrayList fds = new ArrayList();
ArrayList peers = new ArrayList();
FileDescriptor[] fdArray = new FileDescriptor[4];
fds.add(sServerSocket.getFileDescriptor());
peers.add(null);
int loopCount = GC_LOOP_COUNT;
while (true) {
int index;
/*
* Call gc() before we block in select().
* It's work that has to be done anyway, and it's better
* to avoid making every child do it. It will also
* madvise() any free memory as a side-effect.
*
* Don't call it every time, because walking the entire
* heap is a lot of overhead to free a few hundred bytes.
*/
if (loopCount <= 0) {
gc();
loopCount = GC_LOOP_COUNT;
} else {
loopCount--;
}
try {
fdArray = fds.toArray(fdArray);
index = selectReadable(fdArray);
} catch (IOException ex) {
throw new RuntimeException("Error in select()", ex);
}
if (index < 0) {
throw new RuntimeException("Error in select()");
} else if (index == 0) {
ZygoteConnection newPeer = acceptCommandPeer();
peers.add(newPeer);
fds.add(newPeer.getFileDesciptor());
} else {
boolean done;
done = peers.get(index).runOnce();
if (done) {
peers.remove(index);
fds.remove(index);
}
}
}
}
从Socket中读取参数传递到fds，然后解析index，当index>0时，通过runOnce函数来处理Socket请求。
然后来看runOnce的实现，
源码位置：http://androidxref.com/4.4.4_r1/xref/frameworks/base/core/java/com/android/internal/os/ZygoteConnection.java
boolean runOnce() throws ZygoteInit.MethodAndArgsCaller {
String args[];
Arguments parsedArgs = null;
FileDescriptor[] descriptors;
try {
args = readArgumentList();
descriptors = mSocket.getAncillaryFileDescriptors();
} catch (IOException ex) {
Log.w(TAG, "IOException on command socket " + ex.getMessage());
closeSocket();
return true;
}
if (args == null) {
// EOF reached.
closeSocket();
return true;
}
/** the stderr of the most recent request, if avail */
PrintStream newStderr = null;
if (descriptors != null && descriptors.length >= 3) {
newStderr = new PrintStream(
new FileOutputStream(descriptors[2]));
}
int pid = -1;
FileDescriptor childPipeFd = null;
FileDescriptor serverPipeFd = null;
try {
parsedArgs = new Arguments(args);
applyUidSecurityPolicy(parsedArgs, peer, peerSecurityContext);
applyRlimitSecurityPolicy(parsedArgs, peer, peerSecurityContext);
applyCapabilitiesSecurityPolicy(parsedArgs, peer, peerSecurityContext);
applyInvokeWithSecurityPolicy(parsedArgs, peer, peerSecurityContext);
applyseInfoSecurityPolicy(parsedArgs, peer, peerSecurityContext);
applyDebuggerSystemProperty(parsedArgs);
applyInvokeWithSystemProperty(parsedArgs);
int[][] rlimits = null;
if (parsedArgs.rlimits != null) {
rlimits = parsedArgs.rlimits.toArray(intArray2d);
}
if (parsedArgs.runtimeInit && parsedArgs.invokeWith != null) {
FileDescriptor[] pipeFds = Libcore.os.pipe();
childPipeFd = pipeFds[1];
serverPipeFd = pipeFds[0];
ZygoteInit.setCloseOnExec(serverPipeFd, true);
}
pid = Zygote.forkAndSpecialize(parsedArgs.uid, parsedArgs.gid, parsedArgs.gids,
parsedArgs.debugFlags, rlimits, parsedArgs.mountExternal, parsedArgs.seInfo,
parsedArgs.niceName);
} catch (IOException ex) {
logAndPrintError(newStderr, "Exception creating pipe", ex);
} catch (ErrnoException ex) {
logAndPrintError(newStderr, "Exception creating pipe", ex);
} catch (IllegalArgumentException ex) {
logAndPrintError(newStderr, "Invalid zygote arguments", ex);
} catch (ZygoteSecurityException ex) {
logAndPrintError(newStderr,
"Zygote security policy prevents request: ", ex);
}
try {
if (pid == 0) {
// in child
IoUtils.closeQuietly(serverPipeFd);
serverPipeFd = null;
handleChildProc(parsedArgs, descriptors, childPipeFd, newStderr);
// should never get here, the child is expected to either
// throw ZygoteInit.MethodAndArgsCaller or exec().
return true;
} else {
// in parent...pid of < 0 means failure
IoUtils.closeQuietly(childPipeFd);
childPipeFd = null;
return handleParentProc(pid, descriptors, serverPipeFd, parsedArgs);
}
} finally {
IoUtils.closeQuietly(childPipeFd);
IoUtils.closeQuietly(serverPipeFd);
}
}
首先通过readArgumentList()函数来读取传入的所要创建的进程的参数，将之放到Arguments类型的参数parsedArgs中，然后将parseArgs参数传入到forkAndSpecialize函数，通过forkAndSpecialize函数fork一个子进程，然后检测pid是否为0来判断当前进程是否是子进程，是的话就执行handleChildProc函数来处理子进程，否则就进入下一段代码执行handleParentProc处理父进程（记录子进程pid已经应用描述等信息）。
下面来看处理子进程的流程：
源码位置同上也是在ZygoteConnection.java中
private void handleChildProc(Arguments parsedArgs, FileDescriptor[] descriptors, FileDescriptor pipeFd, PrintStream newStderr)
throws ZygoteInit.MethodAndArgsCaller {
closeSocket();
ZygoteInit.closeServerSocket();
if (descriptors != null) {
try {
ZygoteInit.reopenStdio(descriptors[0],
descriptors[1], descriptors[2]);
for (FileDescriptor fd: descriptors) {
IoUtils.closeQuietly(fd);
}
newStderr = System.err;
} catch (IOException ex) {
Log.e(TAG, "Error reopening stdio", ex);
}
}
if (parsedArgs.niceName != null) {
Process.setArgV0(parsedArgs.niceName);
}
if (parsedArgs.runtimeInit) {
if (parsedArgs.invokeWith != null) {
WrapperInit.execApplication(parsedArgs.invokeWith,
parsedArgs.niceName, parsedArgs.targetSdkVersion,
pipeFd, parsedArgs.remainingArgs);
} else {
RuntimeInit.zygoteInit(parsedArgs.targetSdkVersion,
parsedArgs.remainingArgs);
}
} else {
String className;
try {
className = parsedArgs.remainingArgs[0];
} catch (ArrayIndexOutOfBoundsException ex) {
logAndPrintError(newStderr,
"Missing required class name argument", null);
return;
}
String[] mainArgs = new String[parsedArgs.remainingArgs.length - 1];
System.arraycopy(parsedArgs.remainingArgs, 1,
mainArgs, 0, mainArgs.length);
if (parsedArgs.invokeWith != null) {
WrapperInit.execStandalone(parsedArgs.invokeWith,
parsedArgs.classpath, className, mainArgs);
} else {
ClassLoader cloader;
if (parsedArgs.classpath != null) {
cloader = new PathClassLoader(parsedArgs.classpath,
ClassLoader.getSystemClassLoader());
} else {
cloader = ClassLoader.getSystemClassLoader();
}
try {
ZygoteInit.invokeStaticMain(cloader, className, mainArgs);
} catch (RuntimeException ex) {
logAndPrintError(newStderr, "Error starting.", ex);
}
}
}
}
首先是读取描述信息等，这里的nicename不太明白是什么意思，暂时理解为应用信息的一个参数吧，重点是这一段代码:
if (parsedArgs.runtimeInit) {
if (parsedArgs.invokeWith != null) {
WrapperInit.execApplication(parsedArgs.invokeWith,
parsedArgs.niceName, parsedArgs.targetSdkVersion,
pipeFd, parsedArgs.remainingArgs);
} else {
RuntimeInit.zygoteInit(parsedArgs.targetSdkVersion,
parsedArgs.remainingArgs);
}
runtimeInit这个参数之前在添加参数的时候是加过的，所以这里一定是true，invokeWith 参数是没有添加的，所以执行的是RuntimeInit.zygoteInit(parsedArgs.targetSdkVersion,parsedArgs.remainingArgs);也就是运行时初始化。
接着往下看运行时初始化的过程：
public static final void zygoteInit(int targetSdkVersion, String[] argv)
throws ZygoteInit.MethodAndArgsCaller {
if (DEBUG) Slog.d(TAG, "RuntimeInit: Starting application from zygote");
redirectLogStreams();
commonInit();
nativeZygoteInit();
applicationInit(targetSdkVersion, argv);
}
zygoteInit是RuntimeInit类的一个静态成员函数，通过commonInit设置新应用的时区和键盘布局等通用信息，通过nativeZygoteInit()在新的应用程序中创建一个Binder线程池，最后通过applicationInit进入application初始化过程，下面分开来看创建进程池和application初始化过程。
二，线程池创建
上面说到通过nativeZygoteInit()在新的进程中创建Binder线程池，在2.3的代码中这个函数也叫做zygoteInitNative，我们还是继续使用4.4的代码来看，从名字可见这是一个jni函数,实现函数名为com_android_internal_os_RuntimeInit_nativeZygoteInit
private static final native void nativeZygoteInit();
源码位置：http://androidxref.com/4.4.4_r1/xref/frameworks/base/core/jni/AndroidRuntime.cpp
static void com_android_internal_os_RuntimeInit_nativeZygoteInit(JNIEnv* env, jobject clazz)
{
gCurRuntime->onZygoteInit();
}
gCurRuntime是一个全局变量，他是在AndroidRuntime类的构造函数中初始化的，Zygote进程启动时会创建一个AppRuntime类，由于AppRuntime类继承了AndroidRuntime类，所以会导致AndroidRuntime类的构造函数被调用，调用过程中gCurRuntime变量会被初始化，指向的就是正在创建的AppRuntime对象。又因为每创建一个应用进程都会fork一个Zygote进程的地址空间，因此每一个应用进程中都存在一个gCurRuntime全局变量。所以这里调用的是AppRuntime的成员函数onZygoteInit()。
源码地址：http://androidxref.com/4.4.4_r1/xref/frameworks/base/cmds/app_process/app_main.cpp
virtual void onZygoteInit()
{
// Re-enable tracing now that we're no longer in Zygote.
atrace_set_tracing_enabled(true);
sp proc = ProcessState::self();
ALOGV("App process: starting thread pool.\n");
proc->startThreadPool();
}
调用当前应用进程中的ProcessState对象的成员函数startThreadPool来启动一个Binder线程池；
ProcessState.startThreadPool();
源码位置：http://androidxref.com/4.4.4_r1/xref/frameworks/native/libs/binder/ProcessState.cpp
void ProcessState::startThreadPool()
{
AutoMutex _l(mLock);
if (!mThreadPoolStarted) {
mThreadPoolStarted = true;
spawnPooledThread(true);
}
}
Android系统中每个支持Binder进程间通信的进程都有唯一一个
ProcessState对象，当这个对象的成员函数startThreadPool第一次被调用时就会启动Binder进程池，并且将mThreadPoolStarted的值设为true，避免之后重复启动。
这里可以看到先将mThreadStarted参数设置为true，避免之后重复启动线程池，然后调用spawnPooledThread函数。
void ProcessState::spawnPooledThread(bool isMain)
{
if (mThreadPoolStarted) {
String8 name = makeBinderThreadName();
ALOGV("Spawning new pooled thread, name=%s\n", name.string());
sp t = new PoolThread(isMain);
t->run(name.string());
}
}
上一段代码可见这里的isMain参数为true，表示：线程t是进程主动创建来加如到它的Binder线程池的，以区别于Binder驱动程序请求进程创建新的线程来加入到它的Binder线程池的情况。
new一个PoolThread对象，然后调用它的成员函数run，并将线程名传入作为参数。
PoolThread类继承了线程类Thread，并且重写了它的线程入口成员函数threadLoop，改写后如下：
class PoolThread : public Thread
{
public:
PoolThread(bool isMain)
: mIsMain(isMain)
{
}
protected:
virtual bool threadLoop()
{
IPCThreadState::self()->joinThreadPool(mIsMain);
return false;
}
const bool mIsMain;
};
调用了IPCThreadState对象的成员函数joinThreadPool将当前线程注册到Binder驱动程序中去成为一个Binder线程，以便Binder驱动程序可以分发进程间通信请求给它处理，joinThreadPool的代码如下：
源码路径：http://androidxref.com/4.4.4_r1/xref/frameworks/native/libs/binder/IPCThreadState.cpp
void IPCThreadState::joinThreadPool(bool isMain)
{
LOG_THREADPOOL("**** THREAD %p (PID %d) IS JOINING THE THREAD POOL\n", (void*)pthread_self(), getpid());
mOut.writeInt32(isMain ? BC_ENTER_LOOPER : BC_REGISTER_LOOPER);
// This thread may have been spawned by a thread that was in the background
// scheduling group, so first we will make sure it is in the foreground
// one to avoid performing an initial transaction in the background.
set_sched_policy(mMyThreadId, SP_FOREGROUND);
status_t result;
do {
processPendingDerefs();
// now get the next command to be processed, waiting if necessary
result = getAndExecuteCommand();
if (result < NO_ERROR && result != TIMED_OUT && result != -ECONNREFUSED && result != -EBADF) {
ALOGE("getAndExecuteCommand(fd=%d) returned unexpected error %d, aborting",
mProcess->mDriverFD, result);
abort();
}
// Let this thread exit the thread pool if it is no longer
// needed and it is not the main process thread.
if(result == TIMED_OUT && !isMain) {
break;
}
} while (result != -ECONNREFUSED && result != -EBADF);
LOG_THREADPOOL("**** THREAD %p (PID %d) IS LEAVING THE THREAD POOL err=%p\n",
(void*)pthread_self(), getpid(), (void*)result);
mOut.writeInt32(BC_EXIT_LOOPER);
talkWithDriver(false);
}
mOut.writeInt32(isMain ? BC_ENTER_LOOPER : BC_REGISTER_LOOPER);这里的isMain值为true，所以将BC_ENTER_LOOPER命令写入到IPCThreadState类内部的命令协议缓冲区mOut中，最后通过talkWithDriver将命令发送给Binder驱动程序，完成注册。
第一部分中说到Zygote收到AMS传来的参数和命令之后会执行两个动作，一个是通过nativeZygoteInit()来启动线程池，另一个就是接下来要说的通过applicationInit完成application初始化的过程。
三，Application初始化
applicationInit代码如下：
源码路径：http://androidxref.com/4.4.4_r1/xref/frameworks/base/core/java/com/android/internal/os/RuntimeInit.java#applicationInit
private static void applicationInit(int targetSdkVersion, String[] argv)
throws ZygoteInit.MethodAndArgsCaller {
// If the application calls System.exit(), terminate the process
// immediately without running any shutdown hooks. It is not possible to
// shutdown an Android application gracefully. Among other things, the
// Android runtime shutdown hooks close the Binder driver, which can cause
// leftover running threads to crash before the process actually exits.
nativeSetExitWithoutCleanup(true);
// We want to be fairly aggressive about heap utilization, to avoid
// holding on to a lot of memory that isn't needed.
VMRuntime.getRuntime().setTargetHeapUtilization(0.75f);
VMRuntime.getRuntime().setTargetSdkVersion(targetSdkVersion);
final Arguments args;
try {
args = new Arguments(argv);
} catch (IllegalArgumentException ex) {
Slog.e(TAG, ex.getMessage());
// let the process exit
return;
}
// Remaining arguments are passed to the start class's static main
invokeStaticMain(args.startClass, args.startArgs);
}
重点是最后一行，获取传入参数后调用invokeStaticMain函数：
private static void invokeStaticMain(String className, String[] argv)
throws ZygoteInit.MethodAndArgsCaller {
Class cl;
try {
cl = Class.forName(className);
} catch (ClassNotFoundException ex) {
throw new RuntimeException(
"Missing class when invoking static main " + className,
ex);
}
Method m;
try {
m = cl.getMethod("main", new Class[] { String[].class });
} catch (NoSuchMethodException ex) {
throw new RuntimeException(
"Missing static main on " + className, ex);
} catch (SecurityException ex) {
throw new RuntimeException(
"Problem getting static main on " + className, ex);
}
int modifiers = m.getModifiers();
if (! (Modifier.isStatic(modifiers) && Modifier.isPublic(modifiers))) {
throw new RuntimeException(
"Main method is not public and static on " + className);
}
/*
* This throw gets caught in ZygoteInit.main(), which responds
* by invoking the exception's run() method. This arrangement
* clears up all the stack frames that were required in setting
* up the process.
*/
throw new ZygoteInit.MethodAndArgsCaller(m, argv);
}
通过第一部分AMS指定参数可知，这里传入的className的值为android.app.ActivityThread,其中这行代码cl = Class.forName(className);使用装载当前类的类装载器来装载android.app.ActivityThread类，在2.3版本的代码中此处为cl = loader.loadClass(className)二者的区别在于后者只是将信息装载给jvm，需要手动制定装载器的实例。
然后获取android.app.ActivityThread的main函数保存到Method对象m中，最后将这个method封装到一个MethodAndArgsCaller对象中，并将这个MethodAndArgsCaller对象作为一个异常抛给当前应用进程处理，
public static void main(String argv[]) {
try {
··· ···
}catch (MethodAndArgsCaller caller) {
caller.run();
}
当前进程收到异常后直接运行MethodAndArgsCaller对象的run()方法。
MethodAndArgsCaller.run():
源码路径：http://androidxref.com/4.4.4_r1/xref/frameworks/base/core/java/com/android/internal/os/ZygoteInit.java
public static class MethodAndArgsCaller extends Exception
implements Runnable {
/** method to call */
private final Method mMethod;
/** argument array */
private final String[] mArgs;
public MethodAndArgsCaller(Method method, String[] args) {
mMethod = method;
mArgs = args;
}
public void run() {
try {
mMethod.invoke(null, new Object[] { mArgs });
} catch (IllegalAccessException ex) {
throw new RuntimeException(ex);
} catch (InvocationTargetException ex) {
Throwable cause = ex.getCause();
if (cause instanceof RuntimeException) {
throw (RuntimeException) cause;
} else if (cause instanceof Error) {
throw (Error) cause;
}
throw new RuntimeException(ex);
}
}
}
因为这个mMethod对象是封装的android.app.ActivityThread的main方法，所以这里要做的就是main方法的调用。
兜兜转转一大圈回来之后还是调用
android.app.ActivityThread的main方法，那么为什么没有在第一步中直接调用main方法呢？因为新应用程序的一开始需要初始化运行时库以及创建Binder线程池，为了利用java的异常处理机制清理掉前面的调用堆栈，所以要间接的调用main方法。
然后来看main方法的具体实现：
http://androidxref.com/4.4.4_r1/xref/frameworks/base/core/java/android/app/ActivityThread.java
public static void main(String[] args) {
SamplingProfilerIntegration.start();
// CloseGuard defaults to true and can be quite spammy. We
// disable it here, but selectively enable it later (via
// StrictMode) on debug builds, but using DropBox, not logs.
CloseGuard.setEnabled(false);
Environment.initForCurrentUser();
// Set the reporter for event logging in libcore
EventLogger.setReporter(new EventLoggingReporter());
Security.addProvider(new AndroidKeyStoreProvider());
Process.setArgV0("");
Looper.prepareMainLooper();
ActivityThread thread = new ActivityThread();
thread.attach(false);
if (sMainThreadHandler == null) {
sMainThreadHandler = thread.getHandler();
}
AsyncTask.init();
if (false) {
Looper.myLooper().setMessageLogging(new
LogPrinter(Log.DEBUG, "ActivityThread"));
}
Looper.loop();
throw new RuntimeException("Main thread loop unexpectedly exited");
}
通过prepareMainLooper()函数创建一个消息循环，然后new一个ActivityThread：thread，并调用自身的attach()方法，通过getHandler()获取thread的Handle对象，然后再调用loop()函数使thread回到前面的消息循环中，让ActivityThread类一直处于等待消息的工作状态。
消息循环很容易理解，那么attach()类做了什么呢?
http://androidxref.com/4.4.4_r1/xref/frameworks/base/core/java/android/app/ActivityThread.java#attach
private void attach(boolean system) {
sCurrentActivityThread = this;
mSystemThread = system;
if (!system) {
ViewRootImpl.addFirstDrawHandler(new Runnable() {
@Override
public void run() {
ensureJitEnabled();
}
});
android.ddm.DdmHandleAppName.setAppName("",
UserHandle.myUserId());
RuntimeInit.setApplicationObject(mAppThread.asBinder());
IActivityManager mgr = ActivityManagerNative.getDefault();
try {
mgr.attachApplication(mAppThread);
} catch (RemoteException ex) {
// Ignore
}
} else {
// Don't set application object here -- if the system crashes,
// we can't display an alert, we just want to die die die.
android.ddm.DdmHandleAppName.setAppName("system_process",
UserHandle.myUserId());
try {
mInstrumentation = new Instrumentation();
ContextImpl context = ContextImpl.createAppContext(
this, getSystemContext().mPackageInfo);
Application app = Instrumentation.newApplication(Application.class, context);
mAllApplications.add(app);
mInitialApplication = app;
app.onCreate();
} catch (Exception e) {
throw new RuntimeException(
"Unable to instantiate Application():" + e.toString(), e);
}
}
// add dropbox logging to libcore
DropBox.setReporter(new DropBoxReporter());
ViewRootImpl.addConfigCallback(new ComponentCallbacks2() {
@Override
public void onConfigurationChanged(Configuration newConfig) {
synchronized (mResourcesManager) {
// We need to apply this change to the resources
// immediately, because upon returning the view
// hierarchy will be informed about it.
if (mResourcesManager.applyConfigurationToResourcesLocked(newConfig, null)) {
// This actually changed the resources! Tell
// everyone about it.
if (mPendingConfiguration == null ||
mPendingConfiguration.isOtherSeqNewer(newConfig)) {
mPendingConfiguration = newConfig;
sendMessage(H.CONFIGURATION_CHANGED, newConfig);
}
}
}
}
@Override
public void onLowMemory() {
}
@Override
public void onTrimMemory(int level) {
}
});
}
从上一步代码可见传入参数是false，那么将执行第一个if判断里的内容，直接看核心代码：
IActivityManager mgr = ActivityManagerNative.getDefault();
try {
mgr.attachApplication(mAppThread);
} catch (RemoteException ex) {
// Ignore
首先实例化一个IActivityManager对象，然后调用它的attachApplication方法，来看下这个方法具体实现：
http://androidxref.com/4.4.4_r1/xref/frameworks/base/services/java/com/android/server/am/ActivityManagerService.java
public final void attachApplication(IApplicationThread thread) {
synchronized (this) {
int callingPid = Binder.getCallingPid();
final long origId = Binder.clearCallingIdentity();
attachApplicationLocked(thread, callingPid);
Binder.restoreCallingIdentity(origId);
}
}
主要是调用了attachApplicationLocked函数：
private final boolean attachApplicationLocked(IApplicationThread thread,
int pid) {
....
try {
...
thread.bindApplication(processName, appInfo, providers, app.instrumentationClass,
profilerInfo, app.instrumentationArguments, app.instrumentationWatcher,
app.instrumentationUiAutomationConnection, testMode,
mBinderTransactionTrackingEnabled, enableTrackAllocation,
isRestrictedBackupMode || !normalMode, app.persistent,
new Configuration(mConfiguration), app.compat,
getCommonServicesLocked(app.isolated),
mCoreSettingsObserver.getCoreSettingsLocked());
//...
} catch (Exception e) {
return false;
}
....
其中调用的thread.bindApplication()实现如下：
源码路径：http://androidxref.com/4.4.4_r1/xref/frameworks/base/core/java/android/app/ActivityThread.java
public final void bindApplication(String processName,
ApplicationInfo appInfo, List providers,
ComponentName instrumentationName, String profileFile,
ParcelFileDescriptor profileFd, boolean autoStopProfiler,
Bundle instrumentationArgs, IInstrumentationWatcher instrumentationWatcher,
IUiAutomationConnection instrumentationUiConnection, int debugMode,
boolean enableOpenGlTrace, boolean isRestrictedBackupMode, boolean persistent,
Configuration config, CompatibilityInfo compatInfo, Map services,
Bundle coreSettings) {
if (services != null) {
// Setup the service cache in the ServiceManager
ServiceManager.initServiceCache(services);
}
setCoreSettings(coreSettings);
AppBindData data = new AppBindData();
data.processName = processName;
data.appInfo = appInfo;
data.providers = providers;
data.instrumentationName = instrumentationName;
data.instrumentationArgs = instrumentationArgs;
data.instrumentationWatcher = instrumentationWatcher;
data.instrumentationUiAutomationConnection = instrumentationUiConnection;
data.debugMode = debugMode;
data.enableOpenGlTrace = enableOpenGlTrace;
data.restrictedBackupMode = isRestrictedBackupMode;
data.persistent = persistent;
data.config = config;
data.compatInfo = compatInfo;
data.initProfileFile = profileFile;
data.initProfileFd = profileFd;
data.initAutoStopProfiler = false;
sendMessage(H.BIND_APPLICATION, data);
}
先把参数初始化，然后sendMessage到Handler中处理，
public void handleMessage(Message msg) {
if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + codeToString(msg.what));
switch (msg.what) {
case BIND_APPLICATION:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "bindApplication");
AppBindData data = (AppBindData)msg.obj;
handleBindApplication(data);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
}
if (DEBUG_MESSAGES) Slog.v(TAG, "<<< done: " + codeToString(msg.what));
}
在handler处理中调用了handleBindApplication函数：
private void handleBindApplication(AppBindData data) {
mBoundApplication = data;
mConfiguration = new Configuration(data.config);
mCompatConfiguration = new Configuration(data.config);
mProfiler = new Profiler();
mProfiler.profileFile = data.initProfileFile;
mProfiler.profileFd = data.initProfileFd;
mProfiler.autoStopProfiler = data.initAutoStopProfiler;
// send up app name; do this *before* waiting for debugger
Process.setArgV0(data.processName);
android.ddm.DdmHandleAppName.setAppName(data.processName,
UserHandle.myUserId());
if (data.persistent) {
// Persistent processes on low-memory devices do not get to
// use hardware accelerated drawing, since this can add too much
// overhead to the process.
if (!ActivityManager.isHighEndGfx()) {
HardwareRenderer.disable(false);
}
}
if (mProfiler.profileFd != null) {
mProfiler.startProfiling();
}
// If the app is Honeycomb MR1 or earlier, switch its AsyncTask
// implementation to use the pool executor. Normally, we use the
// serialized executor as the default. This has to happen in the
// main thread so the main looper is set right.
if (data.appInfo.targetSdkVersion <= android.os.Build.VERSION_CODES.HONEYCOMB_MR1) {
AsyncTask.setDefaultExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
}
/*
* Before spawning a new process, reset the time zone to be the system time zone.
* This needs to be done because the system time zone could have changed after the
* the spawning of this process. Without doing this this process would have the incorrect
* system time zone.
*/
TimeZone.setDefault(null);
/*
* Initialize the default locale in this process for the reasons we set the time zone.
*/
Locale.setDefault(data.config.locale);
/*
* Update the system configuration since its preloaded and might not
* reflect configuration changes. The configuration object passed
* in AppBindData can be safely assumed to be up to date
*/
mResourcesManager.applyConfigurationToResourcesLocked(data.config, data.compatInfo);
mCurDefaultDisplayDpi = data.config.densityDpi;
applyCompatConfiguration(mCurDefaultDisplayDpi);
data.info = getPackageInfoNoCheck(data.appInfo, data.compatInfo);
/**
* Switch this process to density compatibility mode if needed.
*/
if ((data.appInfo.flags&ApplicationInfo.FLAG_SUPPORTS_SCREEN_DENSITIES)
== 0) {
mDensityCompatMode = true;
Bitmap.setDefaultDensity(DisplayMetrics.DENSITY_DEFAULT);
}
updateDefaultDensity();
final ContextImpl appContext = ContextImpl.createAppContext(this, data.info);
if (!Process.isIsolated()) {
final File cacheDir = appContext.getCacheDir();
if (cacheDir != null) {
// Provide a usable directory for temporary files
System.setProperty("java.io.tmpdir", cacheDir.getAbsolutePath());
setupGraphicsSupport(data.info, cacheDir);
} else {
Log.e(TAG, "Unable to setupGraphicsSupport due to missing cache directory");
}
}
/**
* For system applications on userdebug/eng builds, log stack
* traces of disk and network access to dropbox for analysis.
*/
if ((data.appInfo.flags &
(ApplicationInfo.FLAG_SYSTEM |
ApplicationInfo.FLAG_UPDATED_SYSTEM_APP)) != 0) {
StrictMode.conditionallyEnableDebugLogging();
}
/**
* For apps targetting SDK Honeycomb or later, we don't allow
* network usage on the main event loop / UI thread.
*
* Note to those grepping: this is what ultimately throws
* NetworkOnMainThreadException ...
*/
if (data.appInfo.targetSdkVersion > 9) {
StrictMode.enableDeathOnNetwork();
}
if (data.debugMode != IApplicationThread.DEBUG_OFF) {
// XXX should have option to change the port.
Debug.changeDebugPort(8100);
if (data.debugMode == IApplicationThread.DEBUG_WAIT) {
Slog.w(TAG, "Application " + data.info.getPackageName()
+ " is waiting for the debugger on port 8100...");
IActivityManager mgr = ActivityManagerNative.getDefault();
try {
mgr.showWaitingForDebugger(mAppThread, true);
} catch (RemoteException ex) {
}
Debug.waitForDebugger();
try {
mgr.showWaitingForDebugger(mAppThread, false);
} catch (RemoteException ex) {
}
} else {
Slog.w(TAG, "Application " + data.info.getPackageName()
+ " can be debugged on port 8100...");
}
}
// Enable OpenGL tracing if required
if (data.enableOpenGlTrace) {
GLUtils.setTracingLevel(1);
}
// Allow application-generated systrace messages if we're debuggable.
boolean appTracingAllowed = (data.appInfo.flags&ApplicationInfo.FLAG_DEBUGGABLE) != 0;
Trace.setAppTracingAllowed(appTracingAllowed);
/**
* Initialize the default http proxy in this process for the reasons we set the time zone.
*/
IBinder b = ServiceManager.getService(Context.CONNECTIVITY_SERVICE);
if (b != null) {
// In pre-boot mode (doing initial launch to collect password), not
// all system is up. This includes the connectivity service, so don't
// crash if we can't get it.
IConnectivityManager service = IConnectivityManager.Stub.asInterface(b);
try {
ProxyProperties proxyProperties = service.getProxy();
Proxy.setHttpProxySystemProperty(proxyProperties);
} catch (RemoteException e) {}
}
if (data.instrumentationName != null) {
InstrumentationInfo ii = null;
try {
ii = appContext.getPackageManager().
getInstrumentationInfo(data.instrumentationName, 0);
} catch (PackageManager.NameNotFoundException e) {
}
if (ii == null) {
throw new RuntimeException(
"Unable to find instrumentation info for: "
+ data.instrumentationName);
}
mInstrumentationAppDir = ii.sourceDir;
mInstrumentationAppLibraryDir = ii.nativeLibraryDir;
mInstrumentationAppPackage = ii.packageName;
mInstrumentedAppDir = data.info.getAppDir();
mInstrumentedAppLibraryDir = data.info.getLibDir();
ApplicationInfo instrApp = new ApplicationInfo();
instrApp.packageName = ii.packageName;
instrApp.sourceDir = ii.sourceDir;
instrApp.publicSourceDir = ii.publicSourceDir;
instrApp.dataDir = ii.dataDir;
instrApp.nativeLibraryDir = ii.nativeLibraryDir;
LoadedApk pi = getPackageInfo(instrApp, data.compatInfo,
appContext.getClassLoader(), false, true);
ContextImpl instrContext = ContextImpl.createAppContext(this, pi);
try {
java.lang.ClassLoader cl = instrContext.getClassLoader();
mInstrumentation = (Instrumentation)
cl.loadClass(data.instrumentationName.getClassName()).newInstance();
} catch (Exception e) {
throw new RuntimeException(
"Unable to instantiate instrumentation "
+ data.instrumentationName + ": " + e.toString(), e);
}
mInstrumentation.init(this, instrContext, appContext,
new ComponentName(ii.packageName, ii.name), data.instrumentationWatcher,
data.instrumentationUiAutomationConnection);
if (mProfiler.profileFile != null && !ii.handleProfiling
&& mProfiler.profileFd == null) {
mProfiler.handlingProfiling = true;
File file = new File(mProfiler.profileFile);
file.getParentFile().mkdirs();
Debug.startMethodTracing(file.toString(), 8 * 1024 * 1024);
}
} else {
mInstrumentation = new Instrumentation();
}
if ((data.appInfo.flags&ApplicationInfo.FLAG_LARGE_HEAP) != 0) {
dalvik.system.VMRuntime.getRuntime().clearGrowthLimit();
}
// Allow disk access during application and provider setup. This could
// block processing ordered broadcasts, but later processing would
// probably end up doing the same disk access.
final StrictMode.ThreadPolicy savedPolicy = StrictMode.allowThreadDiskWrites();
try {
// If the app is being launched for full backup or restore, bring it up in
// a restricted environment with the base application class.
Application app = data.info.makeApplication(data.restrictedBackupMode, null);
mInitialApplication = app;
// don't bring up providers in restricted mode; they may depend on the
// app's custom Application class
if (!data.restrictedBackupMode) {
List providers = data.providers;
if (providers != null) {
installContentProviders(app, providers);
// For process that contains content providers, we want to
// ensure that the JIT is enabled "at some point".
mH.sendEmptyMessageDelayed(H.ENABLE_JIT, 10*1000);
}
}
// Do this after providers, since instrumentation tests generally start their
// test thread at this point, and we don't want that racing.
try {
mInstrumentation.onCreate(data.instrumentationArgs);
}
catch (Exception e) {
throw new RuntimeException(
"Exception thrown in onCreate() of "
+ data.instrumentationName + ": " + e.toString(), e);
}
try {
mInstrumentation.callApplicationOnCreate(app);
} catch (Exception e) {
if (!mInstrumentation.onException(app, e)) {
throw new RuntimeException(
"Unable to create application " + app.getClass().getName()
+ ": " + e.toString(), e);
}
}
} finally {
StrictMode.setThreadPolicy(savedPolicy);
}
}
代码很长，核心部分如下：
private void handleBindApplication(AppBindData data) {
mBoundApplication = data;
····
Application app;
final StrictMode.ThreadPolicy savedPolicy = StrictMode.allowThreadDiskWrites();
final StrictMode.ThreadPolicy writesAllowedPolicy = StrictMode.getThreadPolicy();
try {
app = data.info.makeApplication(data.restrictedBackupMode, null);
····
try {
mInstrumentation.onCreate(data.instrumentationArgs);
}
try {
mInstrumentation.callApplicationOnCreate(app);
} catch (Exception e) {
if (!mInstrumentation.onException(app, e)) {
throw new RuntimeException(
"Unable to create application " + app.getClass().getName()
+ ": " + e.toString(), e);
}
}
····
}
通过makeApplication函数创建一个Application：
http://androidxref.com/4.4.4_r1/xref/frameworks/base/core/java/android/app/LoadedApk.java
public Application makeApplication(boolean forceDefaultAppClass,
Instrumentation instrumentation) {
if (mApplication != null) {
return mApplication;
}
Application app = null;
String appClass = mApplicationInfo.className;
if (forceDefaultAppClass || (appClass == null)) {
appClass = "android.app.Application";
}
try {
java.lang.ClassLoader cl = getClassLoader();
ContextImpl appContext = ContextImpl.createAppContext(mActivityThread, this);
app = mActivityThread.mInstrumentation.newApplication(
cl, appClass, appContext);
appContext.setOuterContext(app);
} catch (Exception e) {
if (!mActivityThread.mInstrumentation.onException(app, e)) {
throw new RuntimeException(
"Unable to instantiate application " + appClass
+ ": " + e.toString(), e);
}
}
mActivityThread.mAllApplications.add(app);
mApplication = app;
if (instrumentation != null) {
try {
instrumentation.callApplicationOnCreate(app);
} catch (Exception e) {
if (!instrumentation.onException(app, e)) {
throw new RuntimeException(
"Unable to create application " + app.getClass().getName()
+ ": " + e.toString(), e);
}
}
}
return app;
}
获取android.app.Application的完整类名，获取类加载器对象以及上下文，最后调用Instrumentation类的newApplication对象：
http://androidxref.com/4.4.4_r1/xref/frameworks/base/core/java/android/app/Instrumentation.java
public Application newApplication(ClassLoader cl, String className, Context context)
throws InstantiationException, IllegalAccessException,
ClassNotFoundException {
return newApplication(cl.loadClass(className), context);
}
static public Application newApplication(Class clazz, Context context)
throws InstantiationException, IllegalAccessException,
ClassNotFoundException {
Application app = (Application)clazz.newInstance();
app.attach(context);
return app;
}
这里通过反射的方式，创建了 Application 类的实例，并且绑定了 Application 的上下文，注意一下：在handleBindApplication中调用makeApplication时候传入的最后一个参数是null，所以这里的 instrumentation 对象为空，并不会去执行makeApplication中的最后一个if判断中的callApplicationOnCreate()，所以makeApplication中直接返回了新建的这个app变量也就是Application类到handBindApplication中然后执行mInstrumentation.callApplicationOnCreate(app);这行代码，直接调用Application类的OnCreat()方法，而这个方法就是我们写代码的时候主函数中重写的Application的OnCreat()方法.
然后接下来就是执行我们写的应用内部的代码了。
至此我们的应用终于正常启动起来！！！！！！！！！！
4，附录：Application类的源码：
上源码
package android.app;
import android.annotation.CallSuper;
import android.annotation.NonNull;
import android.annotation.Nullable;
import android.compat.annotation.UnsupportedAppUsage;
import android.content.ComponentCallbacks;
import android.content.ComponentCallbacks2;
import android.content.Context;
import android.content.ContextWrapper;
import android.content.Intent;
import android.content.res.Configuration;
import android.os.Bundle;
import android.util.Log;
import android.view.autofill.AutofillManager;
import java.util.ArrayList;
/**
* Base class for maintaining global application state. You can provide your own
* implementation by creating a subclass and specifying the fully-qualified name
* of this subclass as the "android:name" attribute in your
* AndroidManifest.xml's <application> tag. The Application
* class, or your subclass of the Application class, is instantiated before any
* other class when the process for your application/package is created.
*
* Note: There is normally no need to subclass
* Application. In most situations, static singletons can provide the same
* functionality in a more modular way. If your singleton needs a global
* context (for example to register broadcast receivers), include
* {@link android.content.Context#getApplicationContext() Context.getApplicationContext()}
* as a {@link android.content.Context} argument when invoking your singleton's
* getInstance() method.
*
*/
public class Application extends ContextWrapper implements ComponentCallbacks2 {
private static final String TAG = "Application";
@UnsupportedAppUsage
private ArrayList mComponentCallbacks =
new ArrayList();
@UnsupportedAppUsage
private ArrayList mActivityLifecycleCallbacks =
new ArrayList();
@UnsupportedAppUsage
private ArrayList mAssistCallbacks = null;
/** @hide */
@UnsupportedAppUsage
public LoadedApk mLoadedApk;
public interface ActivityLifecycleCallbacks {
/**
* Called as the first step of the Activity being created. This is always called before
* {@link Activity#onCreate}.
*/
default void onActivityPreCreated(@NonNull Activity activity,
@Nullable Bundle savedInstanceState) {
}
/**
* Called when the Activity calls {@link Activity#onCreate super.onCreate()}.
*/
void onActivityCreated(@NonNull Activity activity, @Nullable Bundle savedInstanceState);
/**
* Called as the last step of the Activity being created. This is always called after
* {@link Activity#onCreate}.
*/
default void onActivityPostCreated(@NonNull Activity activity,
@Nullable Bundle savedInstanceState) {
}
/**
* Called as the first step of the Activity being started. This is always called before
* {@link Activity#onStart}.
*/
default void onActivityPreStarted(@NonNull Activity activity) {
}
/**
* Called when the Activity calls {@link Activity#onStart super.onStart()}.
*/
void onActivityStarted(@NonNull Activity activity);
/**
* Called as the last step of the Activity being started. This is always called after
* {@link Activity#onStart}.
*/
default void onActivityPostStarted(@NonNull Activity activity) {
}
/**
* Called as the first step of the Activity being resumed. This is always called before
* {@link Activity#onResume}.
*/
default void onActivityPreResumed(@NonNull Activity activity) {
}
/**
* Called when the Activity calls {@link Activity#onResume super.onResume()}.
*/
void onActivityResumed(@NonNull Activity activity);
/**
* Called as the last step of the Activity being resumed. This is always called after
* {@link Activity#onResume} and {@link Activity#onPostResume}.
*/
default void onActivityPostResumed(@NonNull Activity activity) {
}
/**
* Called as the first step of the Activity being paused. This is always called before
* {@link Activity#onPause}.
*/
default void onActivityPrePaused(@NonNull Activity activity) {
}
/**
* Called when the Activity calls {@link Activity#onPause super.onPause()}.
*/
void onActivityPaused(@NonNull Activity activity);
/**
* Called as the last step of the Activity being paused. This is always called after
* {@link Activity#onPause}.
*/
default void onActivityPostPaused(@NonNull Activity activity) {
}
/**
* Called as the first step of the Activity being stopped. This is always called before
* {@link Activity#onStop}.
*/
default void onActivityPreStopped(@NonNull Activity activity) {
}
/**
* Called when the Activity calls {@link Activity#onStop super.onStop()}.
*/
void onActivityStopped(@NonNull Activity activity);
/**
* Called as the last step of the Activity being stopped. This is always called after
* {@link Activity#onStop}.
*/
default void onActivityPostStopped(@NonNull Activity activity) {
}
/**
* Called as the first step of the Activity saving its instance state. This is always
* called before {@link Activity#onSaveInstanceState}.
*/
default void onActivityPreSaveInstanceState(@NonNull Activity activity,
@NonNull Bundle outState) {
}
/**
* Called when the Activity calls
* {@link Activity#onSaveInstanceState super.onSaveInstanceState()}.
*/
void onActivitySaveInstanceState(@NonNull Activity activity, @NonNull Bundle outState);
/**
* Called as the last step of the Activity saving its instance state. This is always
* called after{@link Activity#onSaveInstanceState}.
*/
default void onActivityPostSaveInstanceState(@NonNull Activity activity,
@NonNull Bundle outState) {
}
/**
* Called as the first step of the Activity being destroyed. This is always called before
* {@link Activity#onDestroy}.
*/
default void onActivityPreDestroyed(@NonNull Activity activity) {
}
/**
* Called when the Activity calls {@link Activity#onDestroy super.onDestroy()}.
*/
void onActivityDestroyed(@NonNull Activity activity);
/**
* Called as the last step of the Activity being destroyed. This is always called after
* {@link Activity#onDestroy}.
*/
default void onActivityPostDestroyed(@NonNull Activity activity) {
}
}
/**
* Callback interface for use with {@link Application#registerOnProvideAssistDataListener}
* and {@link Application#unregisterOnProvideAssistDataListener}.
*/
public interface OnProvideAssistDataListener {
/**
* This is called when the user is requesting an assist, to build a full
* {@link Intent#ACTION_ASSIST} Intent with all of the context of the current
* application. You can override this method to place into the bundle anything
* you would like to appear in the {@link Intent#EXTRA_ASSIST_CONTEXT} part
* of the assist Intent.
*/
public void onProvideAssistData(Activity activity, Bundle data);
}
public Application() {
super(null);
}
/**
* Called when the application is starting, before any activity, service,
* or receiver objects (excluding content providers) have been created.
*
* Implementations should be as quick as possible (for example using
* lazy initialization of state) since the time spent in this function
* directly impacts the performance of starting the first activity,
* service, or receiver in a process.
*
* If you override this method, be sure to call {@code super.onCreate()}.
*
* Be aware that direct boot may also affect callback order on
* Android {@link android.os.Build.VERSION_CODES#N} and later devices.
* Until the user unlocks the device, only direct boot aware components are
* allowed to run. You should consider that all direct boot unaware
* components, including such {@link android.content.ContentProvider}, are
* disabled until user unlock happens, especially when component callback
* order matters.
*/
@CallSuper
public void onCreate() {
}
/**
* This method is for use in emulated process environments. It will
* never be called on a production Android device, where processes are
* removed by simply killing them; no user code (including this callback)
* is executed when doing so.
*/
@CallSuper
public void onTerminate() {
}
@CallSuper
public void onConfigurationChanged(@NonNull Configuration newConfig) {
Object[] callbacks = collectComponentCallbacks();
if (callbacks != null) {
for (int i=0; i();
}
mAssistCallbacks.add(callback);
}
}
public void unregisterOnProvideAssistDataListener(OnProvideAssistDataListener callback) {
synchronized (this) {
if (mAssistCallbacks != null) {
mAssistCallbacks.remove(callback);
}
}
}
/**
* Returns the name of the current process. A package's default process name
* is the same as its package name. Non-default processes will look like
* "$PACKAGE_NAME:$NAME", where $NAME corresponds to an android:process
* attribute within AndroidManifest.xml.
*/
public static String getProcessName() {
return ActivityThread.currentProcessName();
}
// ------------------ Internal API ------------------
/**
* @hide
*/
@UnsupportedAppUsage
/* package */ final void attach(Context context) {
attachBaseContext(context);
mLoadedApk = ContextImpl.getImpl(context).mPackageInfo;
}
@UnsupportedAppUsage
/* package */ void dispatchActivityPreCreated(@NonNull Activity activity,
@Nullable Bundle savedInstanceState) {
Object[] callbacks = collectActivityLifecycleCallbacks();
if (callbacks != null) {
for (int i = 0; i < callbacks.length; i++) {
((ActivityLifecycleCallbacks) callbacks[i]).onActivityPreCreated(activity,
savedInstanceState);
}
}
}
@UnsupportedAppUsage
/* package */ void dispatchActivityCreated(@NonNull Activity activity,
@Nullable Bundle savedInstanceState) {
Object[] callbacks = collectActivityLifecycleCallbacks();
if (callbacks != null) {
for (int i=0; i 0) {
callbacks = mComponentCallbacks.toArray();
}
}
return callbacks;
}
@UnsupportedAppUsage
private Object[] collectActivityLifecycleCallbacks() {
Object[] callbacks = null;
synchronized (mActivityLifecycleCallbacks) {
if (mActivityLifecycleCallbacks.size() > 0) {
callbacks = mActivityLifecycleCallbacks.toArray();
}
}
return callbacks;
}
/* package */ void dispatchOnProvideAssistData(Activity activity, Bundle data) {
Object[] callbacks;
synchronized (this) {
if (mAssistCallbacks == null) {
return;
}
callbacks = mAssistCallbacks.toArray();
}
if (callbacks != null) {
for (int i=0; i Tips：
程序启动时，系统会自动创建 Application 对象，然后运行 onCreate() 方法，其中 android.app.Application.onCreate() 方法体为空，可以在 onCreate() 中做一些初始化工作。Application 不能自己创建，就如同不能自己创建 Activity 一样，如果我们通过 new 创建一个 Application，会得到一个普通的类的实例，如果需要应用 Application 的地方用的是我们 new 出来的实例，则会出现空指针异常。综上所述，使用 Application 一定要使用程序自己创建的 Application，在 onCreate() 中将对象赋值给一个变量（mMyApplication = this），后面开发中使用这个变量即可。
在 Android 应用中，Application 的生命周期是和整个应用一致的，只要应用没有被系统回收，这个 Application 对象就会一直存在。但是这个 Application 对象并不是始终在内存中的，它有可能会由于系统内存不足而被回收。但系统在你重新打开这个应用时并不是重新启动这个 Application 对象，它会创建一个新的 Application 对象并且启动上次用户离开时的 Activity，造成这个 app 从来没有被 kill 掉的假象。这样，之前在 Application 中缓存的数据都会重新初始化。不仅 Application 对象是这样，其它的单例或者公有静态类也有可能会由于系统内存而被杀掉。
参考：
Android系统原代码情景分析（第三版）第五章8.2节：启动Binder线程池
Android系统原代码情景分析（第三版）第12章：安卓应用程序进程的启动过程
Android Application 启动流程源码分析
Android：全面解析 熟悉而陌生 的Application类使用