FLAG_ACTIVITY_REORDER_TO_FRONT之ANR问题(Android L)

Issue: https://code.google.com/p/android/issues/detail?id=169768

问题摘要：
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1)The app starts with Activity A, which simply shows a button called "Launch B". 2)Press this button -- this executes startActivity(FLAG_ACTIVITY_REORDER_TO_FRONT, ActivityB.class). 3)Activity B becomes active, which do some UI and backhand loading operation on UI thread. 4)After pressing back from Activity B, OnBackPressed Of Activity B, this executes startActivity(FLAG_ACTIVITY_REORDER_TO_FRONT, ActivityA.class). 5)Activity A's onResume() is called as expected and everything looks fine (I can see Activity A content again). 6)Press the device's Back key and App freezes for around 10 seconds or more and comes out of application. Without calling onPause(), onDestroy(). (So it may be anr with certain logs) 7)Sometime or may be repeating same above step for 4-5 times it also unfortunately force close googlequicksearchbox

After looking at system logs: found some important logs:

E/ActivityManager( 958): Reason: Input dispatching timed out (Waiting because no window has focus but there is a focused application that may eventually add a window when it finishes starting up.)
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解决方式(workaround):
在FLAG_ACTIVITY_REORDER_TO_FRONT的目标Activity的onNewIntent中用FLAG_ACTIVITY_NEW_TASK start一个创建即消失的activity

示例：

 @Override
    protected void onNewIntent(Intent intent) {
        super.onNewIntent(intent);
         if ((intent.getFlags() & Intent.FLAG_ACTIVITY_REORDER_TO_FRONT) != 0 && Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
          Intent trickIntent = new Intent(context, TrickActivity.class);
         trickIntent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
         startActivity(trickIntent);
         }
    }

其中

public class TrickActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        finish();
    }

    @Override
    public void finish() {
        super.finish();
        // disable the animation
        overridePendingTransition(0, 0);
    }
}