Toast源码分析
Toast源码分析
1、概述
Toast是android中经常使用的提示框，系统通过WindowManager.addView()方法在顶层window窗口添加的视图，所以Toast显示时可以不依赖Activity界面和应用程序当我们把Toast添加到WindowManager进程时，用户应用程序退出时toast依然可以显示并打印，WindowManager和应用程序是不同进程级别的应用所以不会出现子线程更新UI问题（子线程更新UI实质是创建视图线程和更新视图线程不一致导致系统抛出的异常）。
2、原理分析
Toast通过Toast.makeText()方法创建，调用makeText方法时，系统创建Toast实例，并且填充Toast视图布局
public static Toast makeText(Context context, CharSequence text, @Duration int duration) {
Toast result = new Toast(context);
LayoutInflater inflate = (LayoutInflater)
context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
View v = inflate.inflate(com.android.internal.R.layout.transient_notification, null);
TextView tv = (TextView)v.findViewById(com.android.internal.R.id.message);
tv.setText(text);
result.mNextView = v;
result.mDuration = duration;
return result;
}
Toast创建后通过Toast.show()方法显示,在show方法中通过getSerice()方法获取到INotificationManager的代理对象,获取当前Toast创建应用的包名，组装TN对象，通过远程代理调用INotificationManager中的enqueueToast方法，把Toast加入到Toast队列中，并传递包名，TN对象，和显示时长。
public void show() {
if (mNextView == null) {
throw new RuntimeException("setView must have been called");
}
INotificationManager service = getService();
String pkg = mContext.getOpPackageName();
TN tn = mTN;
tn.mNextView = mNextView;
try {
service.enqueueToast(pkg, tn, mDuration);
} catch (RemoteException e) {
// Empty
}
}
static private INotificationManager getService() {
if (sService != null) {
return sService;
}
sService = INotificationManager.Stub.asInterface(ServiceManager.getService("notification"));
return sService;
}
在INotificationManager的实现类中NotificationManagerService.enqueueToast方法中，判断NotificationManager中Toast队列中是否存在当前Toast对象，存在当前对象时更新toast显示时长，第一次添加toast时不存在，,获取Toast显示应用程序是否是系统程序，不是系统程序时限制toast显示数量最多不超过50，不超过50时创建ToastRecord对象，添加到mToastQueue队列中，第一次创建Toast时在ToastRecord中不存在返回-1，创建Toast加入到ToastRecord后赋值为0，通过调用showNextToastLocked方法显示toast视图。
private final IBinder mService = new INotificationManager.Stub() {
// Toasts
// ============================================================================
@Override
public void enqueueToast(String pkg, ITransientNotification callback, int duration)
{
if (DBG) {
Slog.i(TAG, "enqueueToast pkg=" + pkg + " callback=" + callback
+ " duration=" + duration);
}
if (pkg == null || callback == null) {
Slog.e(TAG, "Not doing toast. pkg=" + pkg + " callback=" + callback);
return ;
}
final boolean isSystemToast = isCallerSystem() || ("android".equals(pkg));
final boolean isPackageSuspended =
isPackageSuspendedForUser(pkg, Binder.getCallingUid());
if (ENABLE_BLOCKED_TOASTS && (!noteNotificationOp(pkg, Binder.getCallingUid())
|| isPackageSuspended)) {
if (!isSystemToast) {
Slog.e(TAG, "Suppressing toast from package " + pkg
+ (isPackageSuspended
? " due to package suspended by administrator."
: " by user request."));
return;
}
}
synchronized (mToastQueue) {
int callingPid = Binder.getCallingPid();
long callingId = Binder.clearCallingIdentity();
try {
ToastRecord record;
int index = indexOfToastLocked(pkg, callback);
// If it's already in the queue, we update it in place, we don't
// move it to the end of the queue.
if (index >= 0) {
record = mToastQueue.get(index);
record.update(duration);
} else {
// Limit the number of toasts that any given package except the android
// package can enqueue. Prevents DOS attacks and deals with leaks.
if (!isSystemToast) {
int count = 0;
final int N = mToastQueue.size();
for (int i=0; i= MAX_PACKAGE_NOTIFICATIONS) {
Slog.e(TAG, "Package has already posted " + count
+ " toasts. Not showing more. Package=" + pkg);
return;
}
}
}
}
Binder token = new Binder();
mWindowManagerInternal.addWindowToken(token,
WindowManager.LayoutParams.TYPE_TOAST);
record = new ToastRecord(callingPid, pkg, callback, duration, token);
mToastQueue.add(record);
index = mToastQueue.size() - 1;
keepProcessAliveIfNeededLocked(callingPid);
}
// If it's at index 0, it's the current toast. It doesn't matter if it's
// new or just been updated. Call back and tell it to show itself.
// If the callback fails, this will remove it from the list, so don't
// assume that it's valid after this.
if (index == 0) {
showNextToastLocked();
}
} finally {
Binder.restoreCallingIdentity(callingId);
}
}
}
在showNextToastLocked中，调用record.callback.show方法显示toast视图，record.callback是调用enqueueToast中传递的TN对象，调用tn.show方法发现是通过Handler发送数据给Handler对象处理，在Handler.handleMessage方法中调用handleShow方法，handleShow方法中调用handleHide()方法隐藏以前Toast的视图，通过WindowManager.addView()添加toast视图到顶层的window窗口。
void showNextToastLocked() {
ToastRecord record = mToastQueue.get(0);
while (record != null) {
if (DBG) Slog.d(TAG, "Show pkg=" + record.pkg + " callback=" + record.callback);
try {
record.callback.show(record.token);
scheduleTimeoutLocked(record);
return;
} catch (RemoteException e) {
Slog.w(TAG, "Object died trying to show notification " + record.callback
+ " in package " + record.pkg);
// remove it from the list and let the process die
int index = mToastQueue.indexOf(record);
if (index >= 0) {
mToastQueue.remove(index);
}
keepProcessAliveIfNeededLocked(record.pid);
if (mToastQueue.size() > 0) {
record = mToastQueue.get(0);
} else {
record = null;
}
}
}
}
public void show(IBinder windowToken) {
if (localLOGV) Log.v(TAG, "SHOW: " + this);
mHandler.obtainMessage(0, windowToken).sendToTarget();
}
final Handler mHandler = new Handler() {
@Override
public void handleMessage(Message msg) {
IBinder token = (IBinder) msg.obj;
handleShow(token);
}
};
public void (IBinder windowToken) {
if (localLOGV) Log.v(TAG, "HANDLE SHOW: " + this + " mView=" + mView
+ " mNextView=" + mNextView);
if (mView != mNextView) {
// remove the old view if necessary
handleHide();
mView = mNextView;
Context context = mView.getContext().getApplicationContext();
String packageName = mView.getContext().getOpPackageName();
if (context == null) {
context = mView.getContext();
}
mWM = (WindowManager)context.getSystemService(Context.WINDOW_SERVICE);
// We can resolve the Gravity here by using the Locale for getting
// the layout direction
final Configuration config = mView.getContext().getResources().getConfiguration();
final int gravity = Gravity.getAbsoluteGravity(mGravity, config.getLayoutDirection());
mParams.gravity = gravity;
if ((gravity & Gravity.HORIZONTAL_GRAVITY_MASK) == Gravity.FILL_HORIZONTAL) {
mParams.horizontalWeight = 1.0f;
}
if ((gravity & Gravity.VERTICAL_GRAVITY_MASK) == Gravity.FILL_VERTICAL) {
mParams.verticalWeight = 1.0f;
}
mParams.x = mX;
mParams.y = mY;
mParams.verticalMargin = mVerticalMargin;
mParams.horizontalMargin = mHorizontalMargin;
mParams.packageName = packageName;
mParams.hideTimeoutMilliseconds = mDuration ==
Toast.LENGTH_LONG ? LONG_DURATION_TIMEOUT : SHORT_DURATION_TIMEOUT;
mParams.token = windowToken;
if (mView.getParent() != null) {
if (localLOGV) Log.v(TAG, "REMOVE! " + mView + " in " + this);
mWM.removeView(mView);
}
if (localLOGV) Log.v(TAG, "ADD! " + mView + " in " + this);
mWM.addView(mView, mParams);
trySendAccessibilityEvent();
}
}
在NotificationManagerService中调用record.callback.show()方法后，通过scheduleTimeoutLocked(）方法通过Handler延时发送隐藏toast视图后，重新遍历toastRecord队列显示下个toast。
private void scheduleTimeoutLocked(ToastRecord r)
{
mHandler.removeCallbacksAndMessages(r);
Message m = Message.obtain(mHandler, MESSAGE_TIMEOUT, r);
long delay = r.duration == Toast.LENGTH_LONG ? LONG_DELAY : SHORT_DELAY;
mHandler.sendMessageDelayed(m, delay);
}
mHandler = new WorkerHandler();
private final class WorkerHandler extends Handler
{
@Override
public void handleMessage(Message msg)
{
switch (msg.what)
{
case MESSAGE_TIMEOUT:
handleTimeout((ToastRecord)msg.obj);
break;
case MESSAGE_SAVE_POLICY_FILE:
handleSavePolicyFile();
break;
case MESSAGE_SEND_RANKING_UPDATE:
handleSendRankingUpdate();
break;
case MESSAGE_LISTENER_HINTS_CHANGED:
handleListenerHintsChanged(msg.arg1);
break;
case MESSAGE_LISTENER_NOTIFICATION_FILTER_CHANGED:
handleListenerInterruptionFilterChanged(msg.arg1);
break;
}
}
}
private void handleTimeout(ToastRecord record)
{
if (DBG) Slog.d(TAG, "Timeout pkg=" + record.pkg + " callback=" + record.callback);
synchronized (mToastQueue) {
int index = indexOfToastLocked(record.pkg, record.callback);
if (index >= 0) {
cancelToastLocked(index);
}
}
}
void cancelToastLocked(int index) {
ToastRecord record = mToastQueue.get(index);
try {
record.callback.hide();
} catch (RemoteException e) {
Slog.w(TAG, "Object died trying to hide notification " + record.callback
+ " in package " + record.pkg);
// don't worry about this, we're about to remove it from
// the list anyway
}
ToastRecord lastToast = mToastQueue.remove(index);
mWindowManagerInternal.removeWindowToken(lastToast.token, true);
keepProcessAliveIfNeededLocked(record.pid);
if (mToastQueue.size() > 0) {
// Show the next one. If the callback fails, this will remove
// it from the list, so don't assume that the list hasn't changed
// after this point.
showNextToastLocked();
}
}
3、总结
Toast是通过WindowManager.addView()添加到window窗口的，当把toast添加到NotificationManager中的ToastRecord队列时，应用程序退出后依然显示toast视图，Toast视图是WindowManager进程中显示的，所以调用Toast.show时，可以不考虑线程问题（子线程更新UI实质是创建视图线程和更新视图线程不一致导致系统抛出的异常），但是Toast依赖于Handler消息机制，在子线程中Looper.perpase()没有调用，在子线程中直接使用Toast.show时会抛Can’t create handler inside thread that has not called Looper.prepare()异常，在子线程中打印toast时 可以使用一下方法，在子线程Looper.loop()时子线程会堵塞。
new Thread(new Runnable() {
@Override
public void run() {
Looper.prepare();
Toast.makeText(MainActivity.this,"dfadf",Toast.LENGTH_SHORT).show();
Looper.loop();
Log.e(TAG, "run: " );
}
}).start();