Android9.0上针对Toast的特殊处理图文详解

mToast = new Toast(context);
mToast.setDuration(Toast.LENGTH_LONG);
mToast.setView(layout);
...
mToast.show(); //在线程里不断调用show方法，达到长时间显示的目的

Toast.makeText(mContext, "hello world", duration).show();

mToast = new Toast(context);
mToast.setDuration(Toast.LENGTH_LONG);
mToast.setView(layout);
mToast.show(); 

//frameworks/base/core/java/android/widget/Toast.java
public Toast(@NonNull Context context, @Nullable Looper looper) {
 mContext = context;
 mTN = new TN(context.getPackageName(), looper);
 mTN.mY = context.getResources().getDimensionPixelSize(
  com.android.internal.R.dimen.toast_y_offset);
 mTN.mGravity = context.getResources().getInteger(
  com.android.internal.R.integer.config_toastDefaultGravity);
}

public void setView(View view) {
 mNextView = view;
}

public void setDuration(@Duration int duration) {
 mDuration = duration;
 mTN.mDuration = duration;
}

public void show() {
 if (mNextView == null) {
  throw new RuntimeException("setView must have been called");
 }

 INotificationManager service = getService(); //这里是一个通知服务
 String pkg = mContext.getOpPackageName();
 TN tn = mTN;
 tn.mNextView = mNextView;

 try {
  service.enqueueToast(pkg, tn, mDuration);
 } catch (RemoteException e) {
  // Empty
 }
}

frameworks/base/services/core/java/com/android/server/notification/NotificationManagerService.java

public void enqueueToast(String pkg, ITransientNotification callback, int duration)
 {
  ...
  final boolean isSystemToast = isCallerSystemOrPhone() || ("android".equals(pkg));

  ...
   synchronized (mToastQueue) {
   int callingPid = Binder.getCallingPid();
   long callingId = Binder.clearCallingIdentity();
   try {
    ToastRecord record;
    int index;
    // All packages aside from the android package can enqueue one toast at a time
    if (!isSystemToast) {
     index = indexOfToastPackageLocked(pkg);
    } else {
     index = indexOfToastLocked(pkg, callback);
    }

    // If the package already has a toast, we update its toast
    // in the queue, we don't move it to the end of the queue.
    if (index >= 0) {
     record = mToastQueue.get(index);
     record.update(duration);
     try {
      record.callback.hide();
     } catch (RemoteException e) {
     }
     record.update(callback);
    } else {
     Binder token = new Binder();
     mWindowManagerInternal.addWindowToken(token, TYPE_TOAST, DEFAULT_DISPLAY);
     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);
   }
  }
 }

int indexOfToastLocked(String pkg, ITransientNotification callback)
{
 IBinder cbak = callback.asBinder();
 ArrayList<ToastRecord> list = mToastQueue;
 int len = list.size();
 for (int i=0; i<len; i++) {
  ToastRecord r = list.get(i);
  if (r.pkg.equals(pkg) && r.callback.asBinder().equals(cbak)) {
   return i;
  }
 }
 return -1;
}

record = new ToastRecord(callingPid, pkg, callback, duration, token);
mToastQueue.add(record);
index = mToastQueue.size() - 1;

if (index == 0) {
 showNextToastLocked(); //显示Toast
}

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); //调用TN类的show方法
   scheduleDurationReachedLocked(record); //时间到就隐藏Toast
   return;
  } catch (RemoteException e) {
   ...
  }
 }
}

//frameworks/base/core/java/android/widget/Toast.java
public void show(IBinder windowToken) {
  if (localLOGV) Log.v(TAG, "SHOW: " + this);
  mHandler.obtainMessage(SHOW, windowToken).sendToTarget();
}

//贴出部分handleMessage方法
case SHOW: {
 IBinder token = (IBinder) msg.obj;
 handleShow(token);
 break;
}

public void handleShow(IBinder windowToken) {

 ...
 if (mView != mNextView) {
  // remove the old view if necessary
  handleHide();
  mView = mNextView;
  ...
  mWM = (WindowManager)context.getSystemService(Context.WINDOW_SERVICE);
  ...
  try {
   mWM.addView(mView, mParams); //交给WMS进行下一步的操作，最终显示出我们的view
   trySendAccessibilityEvent();
  } catch (WindowManager.BadTokenException e) {
   /* ignore */
  }
 }

}

//frameworks/base/services/core/java/com/android/server/notification/NotificationManagerService.java
private void scheduleDurationReachedLocked(ToastRecord r)
{
  mHandler.removeCallbacksAndMessages(r);
  Message m = Message.obtain(mHandler, MESSAGE_DURATION_REACHED, r);
  long delay = r.duration == Toast.LENGTH_LONG ? LONG_DELAY : SHORT_DELAY;
  mHandler.sendMessageDelayed(m, delay);
}

case MESSAGE_DURATION_REACHED:
  handleDurationReached((ToastRecord)msg.obj);
  break;

private void handleDurationReached(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(); //隐藏掉该Toast
  } catch (RemoteException e) {
    ...
  }

  ToastRecord lastToast = mToastQueue.remove(index); //已经显示完毕的Toast，从列表中移除掉
  ...
  if (mToastQueue.size() > 0) { //如果还有待显示Toast
    // 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();
  }
}

case HIDE: {
  handleHide();
  // Don't do this in handleHide() because it is also invoked by
  // handleShow()
  mNextView = null; //这里会把view清掉
  break;
}

public void handleHide() {
    if (localLOGV) Log.v(TAG, "HANDLE HIDE: " + this + " mView=" + mView);
    if (mView != null) {
      ...
      mWM.removeViewImmediate(mView);
      ...
      mView = null;
    }
}

if (!isSystemToast) {
    index = indexOfToastPackageLocked(pkg);
  } else {
    index = indexOfToastLocked(pkg, callback);
  }

  // If the package already has a toast, we update its toast
  // in the queue, we don't move it to the end of the queue.
  if (index >= 0) {
    record = mToastQueue.get(index);
    record.update(duration);
    try {
      record.callback.hide(); //如果存在已经显示的Toast，这里会先进行hide
    } catch (RemoteException e) {
    }
    record.update(callback);
  }
}

public void handleShow(IBinder windowToken) {
  // ...
  if (mView != mNextView) {
    // ...
    mView = mNextView;
    // ...
    mWM = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);
    // ...
    mWM.addView(mView, mParams);
    // ...
  }
}

//这里就不执行hide的操作了
if (index >= 0) {
  record = mToastQueue.get(index);
  record.update(duration);
}