android 4.4.X: taskAffinity & launchmode vs. Activ

问题:

I developed a simple application, which demostrates some strange behaviour on Android 4.4.X devices I noticed.

Lets say I want to have 2 "main" activities, where the first says "Hello" (by starting 'HelloActivity') every second time it is resumed and the second one has android:launchMode="singleTask" android:taskAffinity=".MyAffinity" defined. Second one is started by the first one.

My Code

Manifest is pretty simple:

<uses-sdk
    android:minSdkVersion="8"
    android:targetSdkVersion="14" />

<application
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >

    <activity
        android:name="com.example.affinitylaunchmodebugtest.MainActivity"
        android:configChanges="keyboardHidden|orientation|screenSize"
        android:windowSoftInputMode="adjustResize">
        <intent-filter>
            <category android:name="android.intent.category.DEFAULT" />

            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>

    <activity
        android:label="HELLO"
        android:name="com.example.affinitylaunchmodebugtest.HelloActivity"
        android:configChanges="keyboardHidden|orientation|screenSize">
    </activity>

    <activity
        android:label="AffinityTestActivity"
        android:name="com.example.affinitylaunchmodebugtest.AffinityTestActivity"
        android:configChanges="keyboardHidden|orientation|screenSize"
        android:launchMode="singleTask"
        android:taskAffinity=".MyAffinity">
    </activity>
</application>

MainActivity starts AffinityTestActivity on button click and logs its lifecycle. It also starts HelloActivity every second time it is resumed:

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        System.out.println(this+" onCreate");
        super.onCreate(savedInstanceState);

        Button b = new Button(MainActivity.this);
        b.setText("START AFFINITY TEST ACTIVITY");
        b.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                System.out.println(this+" starts "+AffinityTestActivity.class.getSimpleName());
                Intent intent = new Intent(MainActivity.this, AffinityTestActivity.class);
                startActivity(intent);
            }
        });
        setContentView(b);
    }

    private boolean skipHello = true;

    @Override
    protected void onResume() {
        System.out.println(this+" onResume");
        super.onResume();

        if (!skipHello) {
            System.out.println(this+" starts "+HelloActivity.class.getSimpleName());
            Intent intent = new Intent(MainActivity.this, HelloActivity.class);
            startActivity(intent);
            skipHello = true;
        } else {
            skipHello = false;
        }
    }

    @Override
    protected void onPause() {
        System.out.println(this+" onPause");
        super.onPause();
    }

    @Override
    protected void onDestroy() {
        System.out.println(this+" onDestroy");
        super.onDestroy();
    }

}

AffinityTestActivity calls finish() on button click and logs its lifecycle:

public class AffinityTestActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        System.out.println(this+" onCreate");
        super.onCreate(savedInstanceState);

        Button b = new Button(AffinityTestActivity.this);
        b.setText("FINISH");
        b.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                System.out.println(this+" finishes");
                finish();
            }
        });
        setContentView(b);
    }

    @Override
    protected void onResume() {
        System.out.println(this+" onResume");
        super.onResume();
    }

    @Override
    protected void onPause() {
        System.out.println(this+" onPause");
        super.onPause();
    }

    @Override
    protected void onDestroy() {
        System.out.println(this+" onDestroy");
        super.onDestroy();
    }
}

HelloActivity is the same as AffinityTestActivity in fact - it only has button to call finish() and printlns to log its lifecycle.

Test Scenario

1. Start MainActivity.
2. Start AffinityTestActivity.
3. Finish AffinityTestActivity (as AffinityTestActivity finishes, MainActivity is resumed and HelloActivity is started).
4. Analyze output.

Logs

Android 4.4.2 and 4.4.3: (tested on Nexus 7 II and Samsung Galaxy S5) As you can see, log ends with HelloActivity's onPause, which does not make sense (HelloActivity is displayed at top in step 3). Also AffinityTestActivity is not destroyed and MainActivity is not paused.

06-20 11:13:20.547: I/System.out(18650): com.example.affinitylaunchmodebugtest.MainActivity@41f17e50 onCreate
06-20 11:13:20.557: I/System.out(18650): com.example.affinitylaunchmodebugtest.MainActivity@41f17e50 onResume
06-20 11:13:25.371: I/System.out(18650): com.example.affinitylaunchmodebugtest.MainActivity$1@41f6e5c0 starts AffinityTestActivity
06-20 11:13:25.581: I/System.out(18650): com.example.affinitylaunchmodebugtest.MainActivity@41f17e50 onPause
06-20 11:13:25.591: I/System.out(18650): com.example.affinitylaunchmodebugtest.AffinityTestActivity@41f6a480 onCreate
06-20 11:13:25.611: I/System.out(18650): com.example.affinitylaunchmodebugtest.AffinityTestActivity@41f6a480 onResume
06-20 11:13:36.452: I/System.out(18650): com.example.affinitylaunchmodebugtest.AffinityTestActivity$1@41f1ede8 finishes
06-20 11:13:36.662: I/System.out(18650): com.example.affinitylaunchmodebugtest.AffinityTestActivity@41f6a480 onPause
06-20 11:13:36.682: I/System.out(18650): com.example.affinitylaunchmodebugtest.MainActivity@41f17e50 onResume
06-20 11:13:36.682: I/System.out(18650): com.example.affinitylaunchmodebugtest.MainActivity@41f17e50 starts HelloActivity
06-20 11:13:36.782: I/System.out(18650): com.example.affinitylaunchmodebugtest.HelloActivity@41f8dbb8 onCreate
06-20 11:13:36.802: I/System.out(18650): com.example.affinitylaunchmodebugtest.HelloActivity@41f8dbb8 onResume
06-20 11:13:36.852: I/System.out(18650): com.example.affinitylaunchmodebugtest.HelloActivity@41f8dbb8 onPause

Older Android versions (<4.4.2, tested on 2.3.5., 4.1.2 and 4.2.1 devices, 4.0.3 emulator) work as expected - HelloActivity is not paused after onResume and AffinityTestActivity is destroyed:

06-20 11:16:30.867: I/System.out(3296): com.example.affinitylaunchmodebugtest.MainActivity@40f998b0 onCreate
06-20 11:16:30.907: I/System.out(3296): com.example.affinitylaunchmodebugtest.MainActivity@40f998b0 onResume
06-20 11:16:34.157: I/System.out(3296): com.example.affinitylaunchmodebugtest.MainActivity$1@40f9b350 starts AffinityTestActivity
06-20 11:16:34.277: I/System.out(3296): com.example.affinitylaunchmodebugtest.MainActivity@40f998b0 onPause
06-20 11:16:34.297: I/System.out(3296): com.example.affinitylaunchmodebugtest.AffinityTestActivity@40fab810 onCreate
06-20 11:16:34.357: I/System.out(3296): com.example.affinitylaunchmodebugtest.AffinityTestActivity@40fab810 onResume
06-20 11:16:38.687: I/System.out(3296): com.example.affinitylaunchmodebugtest.AffinityTestActivity$1@40fad640 finishes
06-20 11:16:38.707: I/System.out(3296): com.example.affinitylaunchmodebugtest.AffinityTestActivity@40fab810 onPause
06-20 11:16:38.717: I/System.out(3296): com.example.affinitylaunchmodebugtest.MainActivity@40f998b0 onResume
06-20 11:16:38.717: I/System.out(3296): com.example.affinitylaunchmodebugtest.MainActivity@40f998b0 starts HelloActivity
06-20 11:16:38.747: I/System.out(3296): com.example.affinitylaunchmodebugtest.MainActivity@40f998b0 onPause
06-20 11:16:38.777: I/System.out(3296): com.example.affinitylaunchmodebugtest.HelloActivity@40fbdd48 onCreate
06-20 11:16:38.827: I/System.out(3296): com.example.affinitylaunchmodebugtest.HelloActivity@40fbdd48 onResume
06-20 11:16:39.877: I/System.out(3296): com.example.affinitylaunchmodebugtest.AffinityTestActivity@40fab810 onDestroy

My Question(s)

• Why is my HelloActivity paused on Android 4.4.X devices right after it is started and displayed at top?
• How can I avoid it and force the application to have "normal" activity lifecycle, as older Android versions (<4.4.2) do?

I develop application, which is much more complex and works with lifecycle of its activities and this behaviour is violating my application's functionality.

Thank you very much!

回答1:

I've created a project based on the code you provided, and I was able to recreate your issue on my own Nexus 7. While I don't have a concrete, academic answer for you, my best explanation is the following:

1) MainActivity is started

2) Button clicked. AffinityTestActivity is started in a new task.

3) Button clicked. AffinityTestActivity finishes.

4) MainActivity resumes within the old task.

5) In MainActivity's onResume, the intent for HelloActivity is called within the same task.

6) The mysterious part which is my theory after a bit of tinkering: Some part of bringing the old task to the foreground continues to interact with MainActivity, the root of the old task, during its onResume call. This interaction causes the HelloActivity's onPause method to be triggered (probably not intended by the OS developers). While this isn't the most satisfying answer (given my limited experience with OS-level scheduling code and timing issues), my experiments point to something along those lines. My first clue to this interference was this frequent error seen in logcat:

06-24 11:06:28.015  27200-27200/com.stackoverflow I/System.out﹕ com.stackoverflow.MainActivity@64e05830 onPause
06-24 11:06:28.055  27200-27200/com.stackoverflow I/System.out﹕ com.stackoverflow.AffinityTestActivity@64e22fc0 onCreate
06-24 11:06:28.075  27200-27200/com.stackoverflow I/System.out﹕ com.stackoverflow.AffinityTestActivity@64e22fc0 onResume
06-24 11:06:28.175      665-685/? I/ActivityManager﹕ Displayed com.stackoverflow/.AffinityTestActivity: +163ms
06-24 11:06:29.997  27200-27200/com.stackoverflow I/System.out﹕ com.stackoverflow.AffinityTestActivity$1@64e24bf8 finishes
06-24 11:06:30.007  27200-27200/com.stackoverflow I/System.out﹕ com.stackoverflow.AffinityTestActivity@64e22fc0 onPause
06-24 11:06:30.027  27200-27200/com.stackoverflow I/System.out﹕ com.stackoverflow.MainActivity@64e05830 onResume
06-24 11:06:30.027  27200-27200/com.stackoverflow I/System.out﹕ com.stackoverflow.MainActivity@64e05830 starts HelloActivity
06-24 11:06:30.027     665-6346/? I/ActivityManager﹕ START u0 {cmp=com.stackoverflow/.HelloActivity} from pid 27200
06-24 11:06:30.117  27200-27200/com.stackoverflow I/System.out﹕ com.stackoverflow.HelloActivity@64e33b18 onCreate
06-24 11:06:30.127  27200-27200/com.stackoverflow I/System.out﹕ com.stackoverflow.HelloActivity@64e33b18 onResume
06-24 11:06:30.137  27200-27200/com.stackoverflow I/System.out﹕ com.stackoverflow.HelloActivity@64e33b18 onPause
06-24 11:06:30.287      665-685/? I/ActivityManager﹕ Displayed com.stackoverflow/.HelloActivity: +182ms
06-24 11:06:32.389  27200-27200/com.stackoverflow I/System.out﹕ com.stackoverflow.HelloActivity$1@64e356b0 finishes
06-24 11:06:32.389  27200-27200/com.stackoverflow I/System.out﹕ com.stackoverflow.HelloActivity@64e33b18 onDestroy
06-24 11:06:32.399  27200-27200/com.stackoverflow I/System.out﹕ com.stackoverflow.MainActivity@64e05830 onPause
06-24 11:06:32.399  27200-27200/com.stackoverflow E/ActivityThread﹕ Performing pause of activity that is not resumed: {com.stackoverflow/com.stackoverflow.MainActivity}
java.lang.RuntimeException: Performing pause of activity that is not resumed: {com.stackoverflow/com.stackoverflow.MainActivity}
at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3015)
at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3003)
at android.app.ActivityThread.handlePauseActivity(ActivityThread.java:2981)
at android.app.ActivityThread.access$1000(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1207)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5001)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
06-24 11:06:32.409  27200-27200/com.stackoverflow I/System.out﹕ com.stackoverflow.MainActivity@64e05830 onResume
06-24 11:06:32.769  27200-27200/com.stackoverflow I/System.out﹕ com.stackoverflow.AffinityTestActivity@64e22fc0 onDestroy

As you can see, MainActivity's onPause method wasn't even called until after HelloActivity was finished. That's not right either. That, to me, shows that starting an activity within onResume while the task is being brought to the foreground is causing some unintended conflicts in the lifecycle.

To see what happened if I gave the activity/task a second to complete any unseen processing, I used a handler to call the HelloActivity intent in MainActivity:

 @Override
protected void onResume() {
    System.out.println(this + " onResume");
    super.onResume();

    if (!skipHello) {
        System.out.println(this+" starts "+HelloActivity.class.getSimpleName());

        mHandler.postDelayed(new Runnable() {
            @Override
            public void run() {
                Intent intent = new Intent(MainActivity.this, HelloActivity.class);
                startActivity(intent);
            }
        }, 1000);

        skipHello = true;
    } else {
        skipHello = false;
    }
}

This resulted in much better behavior. HelloActivity acted as it should, and onPause wasn't called. Obviously this isn't ideal for working code, but it shows that simply moving execution time forward by a second fixed the problem. More evidence of internal scheduling conflict within the task.

Next, I tried giving HelloActivity its own task as well:

<activity
    android:label="HELLO"
    android:name="com.stackoverflow.HelloActivity"
    android:configChanges="keyboardHidden|orientation|screenSize"
    android:launchMode="singleTask"
    android:taskAffinity=".DifferentTask">
</activity>

(For the record, this configuration doesn't make much sense, but I assume it's reflecting a scenario in your real project that has a more logical purpose.)

Under this scenario, everything works fine. HelloActivity's lifecycle does not interfere with MainActivity's lifecycle. However, it now has the overhead of its own task and the accompanying problems of running an activity as singleTask (hitting the "Home" button and reopening the app will take you to MainActivity, leaving HelloActivity inaccessible in its new task even though it was the last activity viewed before closing the app).

My best recommendation would be to find a way to avoid this particular scenario. :) It seems like it's a bug within later versions of Android, albeit a strange edge case. If that's not an option, you could pursue one of the routes I used to get around it. I've tried a couple other things, but it's difficult to get around the fact that the scheduling is controlled at an OS level outside our grasp.

Sorry that I couldn't get you a more in-depth answer, but that's all I've got for now!