Run split screen view on Android

Question

I want to automatically run the split screen view mode after the app is run. However, I got an error as follows:

"java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myapplication/com.example.myapplication.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.myapplication.MyAccessibilityService.doAction()' on a null object reference"

What did I do wrong? Thanks.

Code:

public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        System.out.println("Main app started!");
        MyAccessibilityService.instance.doAction();
        System.out.println("Main app ended!");
    }
    }




class MyAccessibilityService extends AccessibilityService {

    public static MyAccessibilityService instance;

    protected void onServiceConnected() {
        super.onServiceConnected();

        System.out.println("Accessibility was connected!");
        instance = this;
    }

    @Override
    public void onAccessibilityEvent(AccessibilityEvent event) {
    }

    @Override
    public void onInterrupt() {
    }

    public void doAction(){
        performGlobalAction(GLOBAL_ACTION_TOGGLE_SPLIT_SCREEN);

    }
}