有几种方法可以做到这一点。如果你想创建一个新的实例并关闭当前实例（假设它是在活动堆栈的顶部），你需要设置 Intent.FLAG_ACTIVITY_CLEAR_TOP 。

另外，也可以重新使用活动的同一实例，如果它已经在堆栈的顶部。在这种情况下，你需要将两个 Intent.FLAG_ACTIVITY_CLEAR_TOP 和 Intent.FLAG_ACTIVITY_SINGLE_TOP 。如果你这样做，Android将无法创建活动的另一个实例，但会调用 onNewIntent（）您的活动提供新的意图。的

I am not really familiar with intent flags, so please, bear with me.

I am doing an application which displays stuff from a database in a ViewPager. I also have a widget which from time to time pulls out a random row and displays it. Now, when I click on it, I am taken to an activity where the same content is displayed and now I can take action on it.

Everything works, however when I have an activity already running and then click on the widget, it seems it creates a new instance, because when I press the Back button I am not exiting the application but am taken to the previous instance or something.

Is there a way to start a new instance of an activity and if there were some previous instances running close them, using flags?

I played around with CLEAR_TOP and that stuff but I honestly don't know what am I doing.

Thanks!

//EDIT

Intent.FLAG_ACTIVITY_CLEAR_TOP doesn't seem to do anything. Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_SINGLE_TOP seems to bring the previous one to the top and ignores the new one or something. Maybe let me rephrase, I start the activity from launcher icon, then I press the Home button and click on widget and it should bring up a new instance where ViewPager.setCurrentItem sets the correct page (same as in widget). If there were no main activity running before, everything is okay, but if it was running, finish it.

MyWidgetProvider extends AppWidgetProvider

@Override
public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) {
    Log.d("MainActivity", "MyWidgetProvider # onUpdate");

    for (int i = 0; i < appWidgetIds.length; i++) {
        int appWidgetId = appWidgetIds[i];

        Intent intent = new Intent(context, MainActivity.class);
        intent.putExtra("from_widget", true);
        //intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_SINGLE_TOP);
        PendingIntent pendingIntent = PendingIntent.getActivity(context, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT);

        RemoteViews views = new RemoteViews(context.getPackageName(), R.layout.widget_layout);
        views.setOnClickPendingIntent(R.id.widget_container, pendingIntent);

        appWidgetManager.updateAppWidget(appWidgetId, views);
    }

}

There are several ways to do this. If you want to create a new instance and close the current instance (assuming that it is on the top of the activity stack) you need to set Intent.FLAG_ACTIVITY_CLEAR_TOP.

Another alternative would be to reuse the same instance of the activity if it is already on the top of the stack. In this case you need to set both Intent.FLAG_ACTIVITY_CLEAR_TOP and Intent.FLAG_ACTIVITY_SINGLE_TOP. If you do this, Android won't create another instance of the activity, but will call onNewIntent() of your activity to deliver the new Intent.