如何在点击返回按钮时从一个片段中调用另一个片段？

Question

I have a MainActivity in my application, from where all the fragments are called using Navigation Drawer. And default fragment of the activity is 'A'. So everytime i open the application, 'A' fragment is called. when I hit 'back' from another fragment B, I want to get to default fragment 'A', as what happens in gmail - from any fragment if we hit back, it returns to default fragment "Primary mails".

I tried calling the 'A' fragment by adding the following code to the onPause() of fragment 'B'.

@Override
public void onPause() {
    super.onPause();

    fragment = new A();
    FragmentTransaction fragTransaction = getFragmentManager().beginTransaction();
                        fragTransaction.replace(R.id.a,fragment ).commit();

}

But when I hit back, fragment 'A' is called for a moment, but then the application closes unexpectedly.

Logcat :

01-14 12:44:42.264: E/WindowManager(4655): android.view.WindowLeaked: Activity com.litchi.iguardian.MainActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView{41da6348 VE.... R.....ID 0,0-513,243} that was originally added here

Whats the correct way of doing this ?

Answer 1

You should customize the behavior when you press the back button, because by default it will destroy launched activity and you see your fragment while callbacks goes from onPause() until onStop() and activity is not visible for you anymore. Just override this method, it must solve the problem:

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    if (keyCode == KeyEvent.KEYCODE_BACK) {
        // your code
        return true;
    }

    return super.onKeyDown(keyCode, event);
}

But yeah, it is for global control, for switching fragments you may also call addToBackStack(); when you want return previous fragment by pressing back button.

Answer 2

to back to previous fragment see below code :

fragmentManager.popBackStack(...);

put this in onBack event

to call popBackStack method you first need to call addToBackStack method while calling fragment

Answer 3

Use this code

android.support.v4.app.Fragment detail = new CurrentClass();
detail.setArguments(bundle);
android.support.v4.app.FragmentManager fragmentManager = getFragmentManager();
fragmentManager.beginTransaction()
.add(R.id.content_frame, detail).addToBackStack("back")
.commit();

Answer 4

无需在onPause（）中编写该代码，您可以在您的主要活动的onBackPressed（）中编写该代码。