android singleinstance activity not single if back button pressed

Question

I encountered an interesting issue, where an Activity is created multiple times, even it is defined as a singleTask or a singelInstance Activity in the manifest. Here is how this can be reproduced. Say, in the main activity:

@Override
protected void onResume() {
    Intent i = new Intent(MainActivity.class, SingleActivity.class);
    startActivity(i);
}

in my SingleActivity, I have:

@Override
protected void onCreate(Bundle savedInstanceState) {
    ...
    Log.i("SingleActivity", "onCreate " + System.identityHashCode(this));
    ...
}

and in the manifest, I have:

    <activity android:name=".SingleActivity"
              android:launchMode="singleInstance"
    />

now, if I start the application, things seem OK, expect in one case: if I press the 'back' button while SingleActivity is in front, it navigates back to MainActivity, where MainActivity.onResume() will create another SingleActivity instance, instead of bringing forward the one that already exists. this is something I know because on the log, a different identity hash code is displayed.

the same seems to be true if the launch mode is singleTask.

the only workaround seems to be to override onBackPressed(), but that seems like an ugly solution.

I wonder what I'm doing wrong

Answer 1

By default, pressing the BACK key finishes (destroys) the current activity and displays the previous activity to the user.

So, this is impossible to

instead of bringing forward the one that already exists

because no activity exists.