FLAG_ACTIVITY_CLEAR_TASK not work with FLAG_ACTIVITY_REORDER_TO_FRONT

Question

I have a problem with an activity which is started with FLAG_ACTIVITY_REORDER_TO_FRONT is not recreated and present on the screen after FLAG_ACTIVITY_CLEAR_TASK.

So the step is:

1. Open app, enter Welcome Activity.
2. Finish Welcome activity and start activity A without specific intent flag.
3. Start activity B with FLAG_ACTIVITY_REORDER_TO_FRONT from activity A (new instance of B is created and now stack became A->B).
4. Start activity A from B with FLAG_ACTIVITY_REORDER_TO_FRONT (existing A instance brought to top of stack so stack became B->A).
5. And under some condition, I need to start over from the beginning (just like another normal app launch), so started Welcome activity using FLAG_ACTIVITY_CLEAR_TASK.

So the app will enter phase 2 again after phase 1, which is what I expected, but then, if I try to start activity B again with FLAG_ACTIVITY_REORDER_TO_FRONT from activity A, there is activity B's callback 'onNewIntent, onStart, onResume' in a row, but it doesn't present on the screen. It looks like to me that there is still the previous instance of activity B somewhere but not showing to me.

I don't specify launch mode for either activity A or B.

I know that document says about FLAG_ACTIVITY_CLEAR_TASK that "This can only be used in conjunction with FLAG_ACTIVITY_NEW_TASK.". And use them together does solve my problem, but then if I click home button to put app background and then launch again, it will become another app launch (enter phase 1) but not back to the previous top activity.

So my questions are:

1. When I use FLAG_ACTIVITY_CLEAR_TASK to start welcome activity, I don't see onDestroy of either activity A or B, is it by design?
2. If they are not destroyed, where do they stay and can I have a reference to them?
3. How can I make activity B presented on the screen after all of these steps?

Code for phase 5:

Intent i = new Intent(A.this, WelcomeActivity.class);
i.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK | Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(i);

Thanks in advance.

AndroidManifest.xml

 <activity
            android:name=".activity.WelcomeActivity"
            android:configChanges="keyboardHidden|orientation|screenSize"
            android:screenOrientation="portrait"
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

<activity
            android:name=".activity.A_Activity"
            android:configChanges="keyboardHidden|orientation|screenSize"
            android:screenOrientation="portrait"
            android:theme="@style/BaiduMapTheme.MainMap"
            android:windowSoftInputMode="adjustPan" />

<activity
            android:name=".activity.B_Activity"
            android:configChanges="locale|fontScale|keyboard|keyboardHidden|layoutDirection|mcc|mnc|navigation|orientation|screenLayout|screenSize|touchscreen|uiMode"
            android:screenOrientation="portrait"
            android:windowSoftInputMode="stateVisible" />

Answer 1

OK, now I think I have those questions because of my incorrect using of the intent flags.

First of all, I should use FLAG_ACTIVITY_CLEAR_TASK and FLAG_ACTIVITY_NEW_TASK at the same time as the document says.

Then everything looks normal and as expected, except one that: if I put the app into background and then click the launch icon again, the WelcomeActivity will be created again.

Previously I thought my existing activity stack is cleared and a new WelcomeActivity is created, but it turns out the existing activity stack is still there, but an extra WelcomeActivity is created, so what I need to do is add some extra flag in WelcomeActivity to determine if it's created in this condition, if yes, then just call finish() in onCreate(), then I can back to the previous activity I was in before enter background.