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本文是探索Activity启动源码的第二篇, 其余参考第一篇.
第一篇的流程图:
第一篇已经探索至关键位置, 即ActivityStackSupervisor的realStartActivityLocked方法, 方法如其名, 从此开始, 才是真正地(Real)启动(Start). Let's start!
ActivityManagerService
ActivityStackSupervisor#realStartActivityLocked:
final boolean realStartActivityLocked(ActivityRecord r, ProcessRecord app,
boolean andResume, boolean checkConfig) throws RemoteException {
// 当屏幕方向修改时, 推迟恢复, 防止冗余启动Activity.
if (checkConfig) {
Configuration config = mWindowManager.updateOrientationFromAppTokens(
mService.mConfiguration,
r.mayFreezeScreenLocked(app) ? r.appToken : null);
mService.updateConfigurationLocked(config, r, false, true /* deferResume */);
}
// 将进程描述符(ProcessRecord)设置入Activity描述符(ActivityRecord)
r.app = app;
app.waitingToKill = null; // 避免在后台被杀死
r.launchCount++; // 增加启动次数
r.lastLaunchTime = SystemClock.uptimeMillis(); // 最新启动时间
// 当Activity描述符不在进程的Activity列表中, 将Activity添加入进程的Activity列表
int idx = app.activities.indexOf(r);
if (idx < 0) {
app.activities.add(r);
}
// AMS更新进程描述符为最少最新使用(LRU).
mService.updateLruProcessLocked(app, true, null);
// ...
try {
// ...
// 远程调用ApplicationThread的scheduleLaunchActivity
app.thread.scheduleLaunchActivity(new Intent(r.intent), r.appToken,
System.identityHashCode(r), r.info, new Configuration(mService.mConfiguration),
new Configuration(task.mOverrideConfig), r.compat, r.launchedFromPackage,
task.voiceInteractor, app.repProcState, r.icicle, r.persistentState, results,
newIntents, !andResume, mService.isNextTransitionForward(), profilerInfo);
// ...
} catch (RemoteException e) {
// ...
}
// ...
return true;
}
ActivityRecord即Activity描述符(变量r), 含有被启动的Activity信息; ProcessRecord即进程描述符(变量app), 含有当前应用的进程信息.
app.thread类型是IApplicationThread, 通过IApplicationThread的代理ApplicationThreadProxy, 远程调用ApplicationThread的scheduleLaunchActivity方法, ApplicationThread是IApplicationThread的最终实现.
启动Activity再次由AMS(ActivityManagerService)通过远程调用(Binder)交给应用进程(ActivityThread)处理. ApplicationThread是ActivityThread的私有类.
ApplicationThread#scheduleLaunchActivity:
@Override
public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,
ActivityInfo info, Configuration curConfig, Configuration overrideConfig,
CompatibilityInfo compatInfo, String referrer, IVoiceInteractor voiceInteractor,
int procState, Bundle state, PersistableBundle persistentState,
List pendingResults, List pendingNewIntents,
boolean notResumed, boolean isForward, ProfilerInfo profilerInfo) {
// ...
// 即来自客户端(AMS)的Activity描述符
ActivityClientRecord r = new ActivityClientRecord();
// 将AMS的Activity描述符, 转换为当前进程的Activity描述符
r.token = token;
// ...
// 封装, 发送启动消息给H类处理, 并传递Activity描述符
sendMessage(H.LAUNCH_ACTIVITY, r);
}
sendMessage是重载方法, 最终调用H类处理数据.
private void sendMessage(int what, Object obj, int arg1, int arg2, boolean async) {
// ...
// 最终由H类(Handler)处理数据
mH.sendMessage(msg);
}
将启动Activity交给ActivityThread的Handler H类处理.
private class H extends Handler {
public void handleMessage(Message msg) {
switch (msg.what) {
case LAUNCH_ACTIVITY: {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStart");
ActivityClientRecord r = (ActivityClientRecord)msg.obj;
// 设置Activity描述符的包信息
r.packageInfo = getPackageInfoNoCheck(r.activityInfo.applicationInfo, r.compatInfo);
// 至此, 完成启动Activity已经由AMS交给当前应用, 在当前应用中启动Activity.
handleLaunchActivity(r, null);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
} break;
}
}
}
启动Activity, 先由当前进程, 通过ActivityManagerNative#getDefault#startActivity方法, 交给AMS处理, AMS管理Activity的Stack和Task, 并设置Activity描述符(Record); 再通过app.thread#scheduleLaunchActivity方法, 继续交给当前进程处理.
AMS切换当前线程的流程图:
ActivityThread
ActivityThread#handleLaunchActivity:
handleLaunchActivity调用performLaunchActivity方法, 继续执行启动, 在成功后, 调用handleResumeActivity方法, 执行显示Activity.
private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent, String reason) {
// 因为当前进程正在活跃, 所以跳过在后台中执行GC.
unscheduleGcIdler();
// ...
// 确保使用最近的环境配置
handleConfigurationChanged(null, null);
if (localLOGV) Slog.v(
TAG, "Handling launch of " + r);
// 在创建Activity前, 初始化WindowManagerGlobal, 即WindowManagerService
WindowManagerGlobal.initialize();
// 执行启动Activity
Activity a = performLaunchActivity(r, customIntent);
// 在启动成功后, 处理恢复Activity
if (a != null) {
r.createdConfig = new Configuration(mConfiguration);
reportSizeConfigurations(r);
Bundle oldState = r.state;
// 恢复Activity
handleResumeActivity(r.token, false, r.isForward,
!r.activity.mFinished && !r.startsNotResumed, r.lastProcessedSeq, reason);
// ...
}
} else {
// 如果发生错误, 则AMS停止启动Activity
try {
ActivityManagerNative.getDefault()
.finishActivity(r.token, Activity.RESULT_CANCELED, null,
Activity.DONT_FINISH_TASK_WITH_ACTIVITY);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
}
}
ActivityThread#performLaunchActivity:
performLaunchActivity方法是Activity启动的核心:
- 获取Activity的组件信息(ComponentName);
- 根据组件使用反射创建Activity(newActivity);
- 将Activity绑定(attach)Application和BaseContext;
- 相继调用onCreate, onStart, onRestoreInstanceState, onPostCreate等方法.
- 放入Activity列表(Map)中统一管理, token是key.
private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
ActivityInfo aInfo = r.activityInfo;
if (r.packageInfo == null) {
// 通过应用信息, 兼容信息, 从PMS, 获取Activity的包信息
r.packageInfo = getPackageInfo(aInfo.applicationInfo, r.compatInfo,
Context.CONTEXT_INCLUDE_CODE);
}
// 获取组件信息
ComponentName component = r.intent.getComponent();
if (component == null) {
component = r.intent.resolveActivity(
mInitialApplication.getPackageManager());
r.intent.setComponent(component);
}
// 当指定Activity时, 使用包名和类名创建组件
if (r.activityInfo.targetActivity != null) {
component = new ComponentName(r.activityInfo.packageName,
r.activityInfo.targetActivity);
}
Activity activity = null;
try {
java.lang.ClassLoader cl = r.packageInfo.getClassLoader();
// 通过反射, 使用ClassLoader创建Activity
activity = mInstrumentation.newActivity(
cl, component.getClassName(), r.intent);
// ...
} catch (Exception e) {
// ...
}
try {
// 使用单例模式, 创建Application
Application app = r.packageInfo.makeApplication(false, mInstrumentation);
// ...
if (activity != null) {
// 创建Activity的上下文BaseContext
Context appContext = createBaseContextForActivity(r, activity);
// ...
// 将Activity绑定上下文appContext, 和应用app
activity.attach(appContext, this, getInstrumentation(), r.token,
r.ident, app, r.intent, r.activityInfo, title, r.parent,
r.embeddedID, r.lastNonConfigurationInstances, config,
r.referrer, r.voiceInteractor, window);
// ...
// 设置主题
int theme = r.activityInfo.getThemeResource();
if (theme != 0) {
activity.setTheme(theme);
}
activity.mCalled = false; // 判断执行是否成功, 成功会置true
// 调用Activity的onCreate方法.
if (r.isPersistable()) {
mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);
} else {
mInstrumentation.callActivityOnCreate(activity, r.state);
}
// ...
// 调用Activity的onStart方法.
if (!r.activity.mFinished) {
activity.performStart();
r.stopped = false;
}
// 调用Activity的onRestoreInstanceState方法.
if (!r.activity.mFinished) {
if (r.isPersistable()) {
if (r.state != null || r.persistentState != null) {
mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state,
r.persistentState);
}
} else if (r.state != null) {
mInstrumentation.callActivityOnRestoreInstanceState(activity, r.state);
}
}
// 调用Activity的onPostCreate方法.
if (!r.activity.mFinished) {
activity.mCalled = false; // 判断执行是否成功, 成功会置true
if (r.isPersistable()) {
mInstrumentation.callActivityOnPostCreate(activity, r.state,
r.persistentState);
} else {
mInstrumentation.callActivityOnPostCreate(activity, r.state);
}
// ...
}
}
r.paused = true;
// 将Activity放入ActivityThread的Activity数组中统一管理.
mActivities.put(r.token, r);
} // ...
return activity;
}
onPostCreate: Called when activity start-up is complete (after onStart() and onRestoreInstanceState(Bundle) have been called). Applications will generally not implement this method; it is intended for system classes to do final initialization after application code has run.
在调用时, 表明Activity已经完全启动, 只剩下显示(onResume).
通过分析performLaunchActivity, 我们也更加清晰Activity的生命周期, 顺序如下, onCreate, onStart, onRestoreInstanceState, onPostCreate. 注意, onStart是Activity处理; 其余三个是Instrumentation处理, 支持继承重写相应方法, 自行处理.
至此, Activity已经完全启动, 并调用相应的生命周期方法.
OK, that's all! Enjoy it!