piusvelte piusvelte - 6 months ago 106
Android Question

How do you use Intent.FLAG_ACTIVITY_CLEAR_TOP to clear the Activity Stack?

I've read through several posts about using this, but must be missing something as it's not working for me. My activity A has launchmode="singleTop" in the manifest. It starts activity B, with launchmode="singleInstance". Activity B opens a browser and receives and intent back, which is why it's singleInstance. I'm trying to override the back button so that the user is sent back to the activity A, and can then press Back to leave the activity, rather than back to activity B again.

// activity B
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (android.os.Build.VERSION.SDK_INT < android.os.Build.VERSION_CODES.ECLAIR
&& keyCode == KeyEvent.KEYCODE_BACK
&& event.getRepeatCount() == 0) onBackPressed();
return super.onKeyDown(keyCode, event);
}
@Override
public void onBackPressed() {
startActivity(new Intent(this, UI.class)
.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_NEW_TASK));
return;
}


After returning from the browser, the stack is...
A,B,Browser,B

I expect this code to change the stack to...
A
... so that pressing back once more takes the user back to the Home Screen.

Instead it seems to change the stack to...
A,B,Browser,B,A
...as though those flags aren't there.

I tried calling finish() in activity B after startActivity, but then the back button takes me back to the browser again!

What am I missing? Thank you!

Answer

@bitestar has the correct solution, but there is one more step:

It was hidden away in the docs, however you must change the launchMode of the Activity to anything other than standard. Otherwise it will be destroyed and recreated instead of being reset to the top.

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