Android-活动片段并返回

Question

In Android, when we replace a container view with a new fragment, we can use replace() and addToBackStack( ), so on pressing back button we goto previous fragment.

But what if the following occurs :

Activity1 (fragment1 -> fragment2 [calls startActivity for Activity2]) -> Activity2

Within Activity1, I can press back button to go from fragment2 to fragment1. But when fragment2 starts another activity, on pressing back button from Activity2, it takes me to fragment1 in Activity1. How can I make back button press from Activity2 come back to fragment2 in Activity1 ?

Code :

// In Activity1 - starts with a ListFragment
@Override
protected void onResume() {
    super.onResume();

    getFragmentManager().beginTransaction()
            .replace(R.id.container, ListFragment.newInstance(0))
            .commit();
}

// In Activity1 , each item in list replaces the container view 
// with new fragment
@Override
public void onItemSelected(int position) {

    if(position == 0) {

        getFragmentManager().beginTransaction()
                .replace(R.id.container, Example1_Fragment.newInstance(0))
                .addToBackStack(null)
                .commit();

    }
   ....
 }

 // In Example1_Fragment

public class Example1_Fragment extends Fragment {

 @Override
 public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

    View view = inflater.inflate(R.layout.example1_fragment, container, false);

    Button btnIntent = (Button) view.findViewById(R.id.btnIntent);
    btnIntent.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            Intent intent = new Intent();
            intent.setAction("com.android.test2.app.example1_action");
            startActivityForResult(intent,1);
        }
    });

    return view;
}

// this is why I want to come back to Example1_Fragment - 
// the activity I start has to send a result back to
// the Example1_Fragment, but on back button, it takes me
// back to the ListFragment, and I cannot take any UI
// action (change to UI) in Example1_Fragment, as the
// ListFragment gets displayed - the onActivityResult of
// Example1_Fragment does get called

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);

    if(requestCode == 1 && resultCode == Activity.RESULT_OK){

             // do something
    }
}

Answer 1

不要在onResume（）回调中替换Fragment1，返回到activity1时将始终调用此方法，请在onCreate（）回调中进行此操作。

Answer 2

You can manually set the back pressed calls inside of this method in your Second Activity. So that when you press back, you can find fragment 2 by its tag and add it back.

@Override
    public void onBackPressed() {
        // TODO Auto-generated method stub
            Intent i = new Intent(this, firstActivity.class);
            startActivity(i);
            FragmentTwo fragmentTwo = manager.findFragmentByTag("fragmentTwoTag");
            manager.beginTransaction.replace(fragmentOne, fragmentTwo).addToBackStack(null).commit();


    }