调用 Activity.Recreate() 后维护我的 Activity 后台堆栈的最佳方法是什么？

Question

I have an Activity that handles many Fragments , and, for backstack management, I have a custom stack, where I manage show / hide for Fragments . My code and navigation work perfectly.

Right now, I am implementing the application theme change by a Button in the Configuration Fragment . For this I am using the method Activity.Recreate (); for the change of the theme and, the data of the Configuration Fragment is retained with the same data and the theme of the application changes perfectly , but the BackStack of Fragments disappears, reason why, when pressing the back button, it leaves the application, instead of sending me back to the Fragment or Previous Activity, from where I accessed the Configuration Fragment .

What is the best way to maintain the backstack of my Activity? This is possible?

Important: only when Activity.Recreate(); is called, because if the Activity is destroyed by any other way, I do not want the BackStack back, I want my Activity clean .

Additional:

• The orientation setting of my application is in portrait mode .
• The launchMode of my Activity is singleTask , it must be so for the type of application I am doing.

Answer 1

From onCreate documentation and this answer.

Add the following logic to your code:

public void onCreate(Bundle savedInstanceState) {
    if (savedInstanceState == null) { 
        // savedInstanceState will be null only when creating the activity for the first time
        backstack = new BackStack(); //init your backstack
    } else {
      // there is a chance that your backstack will be already exists at this point
      // if not:
      // retrieve the backstack with savedInstanceState.getSerializable("stack")
    }
}

And just clear the stack when changing theme, before calling recreate()

// changing theme detected
bacstack.clear();
backstack = null;
recreate();

To save the stack between destruction (onDestroy) and recreation (onCreate) of your activity, Use this method:

@Override
protected void onSaveInstanceState(@NonNull Bundle outState) {
    super.onSaveInstanceState(outState);
    if (backstack != null) // the check isn't necessary, you can just put a null in the bundle
        outState.putSerializable("stack", backstack);
}

the official guide for saving UI state

The onSaveInstanceState method helps your activity to Survive Configuration change and System-initiated process death. link