Why is Android O failing with "does not belong to this FragmentManager!"

I just faced the same issues in the project that I am currently working on when we moved to Android Studio 3 and upgraded the support library to version 26. All of a sudden, without changing the code, we got tons of this exception. In the end I found out the following:

Google added a new "sanity check" in the sources of the v4 Fragment Manager in January this year (not sure into what release that went) that refuses to add a fragment using a Fragment Manager, if it has a target fragment set and the target fragment cannot be found in the active fragments of the same Fragment Manager. The patch is described in detail here

Ealier versions seem to not have cared about that. Took me a few days to update all the areas in our code where fragments that were added using the Support Fragment Manager used the Child Fragment Manager for their subfragments with the parent fragment as target. Well, late penalty for writing bad code.

Recently, my app experienced the same issue when I targeted it for Android O. As a solution, use:

myDialogFragment.show(SettingsFragment.this.getFragmentManager(), TAG);

instead of:

myDialogFragment.show(getFragmentManager(), TAG);
// or  
myDialogFragment.show(getSupportFragmentManager(), TAG);
// or  
myDialogFragment.show(getChildFragmentManager(), TAG);

while working on an app, I encountered the same problem and I solved it by (in kotlin)

chooseRegionFragment.setTargetFragment(this@ParentFragment, REQUEST_CODE_CHOOSE_REGION)

chooseRegionFragment.show(this@ParentFragment.parentFragmentManager, TAG)

it translates to

chooseRegionFragment.setTargetFragment(ParentFragment.this, REQUEST_CODE_CHOOSE_REGION); 

chooseRegionFragment.show(ParentFragment.this.getParentFragmentManager, TAG);

in java

my app work well until upgrade target version to 27 then i face same issue when call setTargetFragment (Fragment fragment, int requestCode)

example:

chooseRegionFragment.setTargetFragment(ParentFragment.this, REQUEST_CODE_CHOOSE_REGION); 

just change to:

chooseRegionFragment.setTargetFragment(getRootParentFragment(this), REQUEST_CODE_CHOOSE_REGION);

getRootParentFragment(this) this method will find root parent of fragments for you

/** 
   * find root parent of fragment 
   */ 
  public static Fragment getRootParentFragment(Fragment fragment) { 
    Fragment parent = fragment.getParentFragment(); 
    if(parent == null) 
      return fragment; 
    else 
      return getRootParentFragment(parent); 
  } 

Use below solution and you do not need to worry about which fragment managers you are dealing with,

Assuming that you must have used a BaseFragment.

First create an interface:

public interface OnRequestUpdateListener {
void onRequestUpdate(final int requestCode, final Intent data);

void setRequestFragment(final BaseFragment requestFragment, int requestCode);

BaseFragment getRequestFragment();

int getRequestCode();

}

Implement that interface in your BaseFragment

public class BaseFragment extends Fragment implements OnRequestUpdateListener {
private BaseFragment requestFragment;

private int requestCode;

@Override
public void onRequestUpdate(int requestCode, Intent data) {
 // you can implement your logic the same way you do in onActivityResult
}

@Override
public void setRequestFragment(BaseFragment requestFragment, int requestCode) {
    this.requestFragment = requestFragment;
    this.requestCode = requestCode;
}

@Override
public BaseFragment getRequestFragment() {
    return requestFragment;
}

@Override
public int getRequestCode() {
    return requestCode;
}

}

Then, replace the setTargetFragment with setRequestFragment and replace getTargetFragment with getRequestFragment.

Here, you could also user onRequestUpdate in place of onActivityResult.

This is a custom solution without bothering about the which fragment manager you are using.

Using getFragmentManager() instead of getChildFragmentManager() would also work but it affects getParentFragment(). If you do not use a getChildFragmentManager() for nested fragment then you will not be able the get the parent fragment by using getParentFragment() in child/nested fragment.