Current activities onResume() is not called when another Activity is launched from lock screen via notification

问题

I have two activities Activity2 and TestActivity. Activity2 shows notification when launched. TestActivity is launched when notification is clicked. Below is the code of Activity2.java.

import android.app.PendingIntent;
import android.content.Intent;
import android.support.v4.app.NotificationCompat;
import android.support.v4.app.NotificationManagerCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import com.droidapp.apptest.R;

public class Activity2 extends AppCompatActivity{

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_2);
        Log.w("app_test", "onCreate()");
        showNotification();
    }
    @Override
    protected void onStart() {
        Log.w("app_test", "onStart()");
        super.onStart();
    }

    @Override
    protected void onRestart() {
        Log.w("app_test", "onRestart()");
        super.onRestart();
    }

    @Override
    protected void onResume() {
        Log.w("app_test", "onResume()");
        super.onResume();
    }
    @Override
    protected void onPause() {
        Log.w("app_test", "onPause()");
        super.onPause();
    }
    @Override
    protected void onStop() {
        Log.w("app_test", "onStop()");
        super.onStop();
    }
    @Override
    protected void onDestroy() {
        Log.w("app_test", "onDestroy()");
        super.onDestroy();
    }
    public void showNotification() {
        Intent intent = new Intent(this, TestActivity.class);
        PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, intent, 0);
        NotificationCompat.Builder mBuilder = new NotificationCompat.Builder(this, "CHANNEL_ID")
                .setSmallIcon(R.mipmap.ic_launcher)
                .setContentTitle("Title")
                .setContentText("Content text")
                .setContentIntent(pendingIntent)
                .setPriority(NotificationCompat.PRIORITY_DEFAULT);
        NotificationManagerCompat.from(this).notify(102, mBuilder.build());
    }
}

Below all lifecycle methods belongs to Activity2.

When Activity2 first time launched. Here onCreate() notification is shown.

W/app_test: onCreate()
W/app_test: onStart()
W/app_test: onResume()

After pressing home button

W/app_test: onPause()
W/app_test: onStop()

After clicking notification TestActivity is launched. Activity2 lifecycle methods aren't called. Everything is working as expected.

If instead of pressing home button, I press power button

W/app_test: onPause()
W/app_test: onStop()

Then click notification from lock screen Activity2 lifecycle methods are called.

W/app_test: onRestart()
W/app_test: onStart()
W/app_test: onStop()

And then TestActivity is launched. Here strange thing is Activity2 onResume() isn't called.

But if I don't click notification, and just unlock screen by swiping onResume() is called.

W/app_test: onRestart()
W/app_test: onStart()
W/app_test: onResume()

In my real application I register BroadcastReceiver on activities onResume() state and unregister it onPause(). Unregistering BroadcastReceiver which wasn't registered causes IllegalStateException. Now I'm avoiding this exception by putting boolean variable.

Question. Is it expected behaviour or bug in android framework?

Edit. Even more strange thing. If I first press home button, then power button and then click notification from lock screen.

W/app_test: onRestart()
W/app_test: onStart()
W/app_test: onResume()
W/app_test: onPause()
W/app_test: onStop()

And then TestActivity is launched.

activity properties in manifest

<activity
        android:name=".activities.Activity2"
        android:theme="@style/AppTheme.NoActionBar" />
<activity android:name=".activities.TestActivity"/>

回答1:

This is as per expected behavior since when you click the notification from lock screen Activity2 is not visible and goes to background behind TestActivity screen and hence its onResume() won't be called. However, when you don't click the notification and just unlock your phone, Activity2 gets visible and its onResume() will be called. Hope it helps.

来源：https://stackoverflow.com/questions/50167202/current-activities-onresume-is-not-called-when-another-activity-is-launched-fr