Android - startActivityForResult immediately triggering onActivityResult

Question

You can't use startActivityForResult() if your activity is being launched as a singleInstance or singleTask. standard or singleTop launch mode will fix the problem.

Additionally make sure the intent does not have the Intent.FLAG_ACTIVITY_NEW_TASK set.

From the docs:

This flag can not be used when the caller is requesting a result from the activity being launched.

I have seen this behavior before, please make sure your destnation activity (that special activity) is not singleInstance in AndroidManifest file. If the Activity is singleInstance, then it will return RESULT_CANCELED before launched!

I'd also like to add that you could call an external app with:
Intent in = caller.getPackageManager().getLaunchIntentForPackage("com.your.package.here");
Which would create an intent with Intent.FLAG_ACTIVITY_NEW_TASK added by default, so call:
in.setFlags(0);
Which will clear that flag, and then you can proceed to: startActivityForResult(in, action);

Reason I'm doing this is that I have a utility app that has common functionality between a few other apps and I can keep the code changes to one location instead of worrying about multiple updates.

startActivityForResult() doesn't work with a singleInstance or singleTask activity in pre-lollipop version of Android. Since Android 5 it works (see this answer for more details).

It also triggers if you have FLAG_ACTIVITY_NEW_TASK in your intent.

Intent intent = new Intent(this, MyActivity.class);
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivityForResult(intent, REQUEST_CODE);

My problem was with the calling activity. Its declaration in the AndroidManifest had the following property:

android:noHistory="true"

Changed it to "false" and now works fine.