Why I'm getting java.lang.IllegalArgumentException during android.support.v4.app.Fragment.setTargetFragment

Question

After upgrading my app to

• targetSdkVersion 27
• com.android.support:support-v4:27.0.2

I am getting the following crash log from live

Caused by: java.lang.IllegalArgumentException:  
  at android.support.v4.app.Fragment.setTargetFragment (Fragment.java:545)

I look at the source code of support fragment (Not exactly line 545. I'm not sure how I can get the latest source code of support fragment library)

https://android.googlesource.com/platform/frameworks/support/+/cef09fe/v4/java/android/support/v4/app/Fragment.java#598

598 public void setTargetFragment(Fragment fragment, int requestCode) {
599     mTarget = fragment;
560     mTargetRequestCode = requestCode;
561 }

I can't see a reason why java.lang.IllegalArgumentException is thrown. Maybe I'm looking at wrong version of support library source code?

Do you have any idea, why I'm getting java.lang.IllegalArgumentException during android.support.v4.app.Fragment.setTargetFragment

---

My source code is as follow

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;

public class BuyPortfolioFragment extends Fragment {

    ...

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ...

        // If not retained (or first time running), we need to create it.
        if (this.statusBarUpdaterFragment == null) {
            this.statusBarUpdaterFragment = StatusBarUpdaterFragment.newInstance();
            // Tell it who it is working with.
            this.statusBarUpdaterFragment.setTargetFragment(this, 0);
            fm.beginTransaction().add(statusBarUpdaterFragment, STATUS_BAR_UPDATER_FRAGMENT).commitAllowingStateLoss();
        } else {
            statusBarUpdaterFragment.setTargetFragment(this, 0);
        }

Answer 1

This is my code, which may crash sometimes. You may reproduce, by reducing background process limit to 1.

public class BuyPortfolioFragment extends Fragment {

    ...

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ...

        // If not retained (or first time running), we need to create it.
        if (this.statusBarUpdaterFragment == null) {
            this.statusBarUpdaterFragment = StatusBarUpdaterFragment.newInstance();
            // Tell it who it is working with.
            this.statusBarUpdaterFragment.setTargetFragment(this, 0);
            fm.beginTransaction().add(statusBarUpdaterFragment, STATUS_BAR_UPDATER_FRAGMENT).commitAllowingStateLoss();
        } else {
            statusBarUpdaterFragment.setTargetFragment(this, 0);
        }

Note, calling setTargetFragment might not be always necessary due to Is calling setTargetFragment on headless fragment no longer necessary during UI fragment re-creation?

However, to play a safe game, I use the following fix.

public class BuyPortfolioFragment extends Fragment {

    ...

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ...

        // If not retained (or first time running), we need to create it.
        if (this.statusBarUpdaterFragment == null) {
            this.statusBarUpdaterFragment = StatusBarUpdaterFragment.newInstance();
            // Tell it who it is working with.
            this.statusBarUpdaterFragment.setTargetFragment(this, 0);
            fm.beginTransaction().add(statusBarUpdaterFragment, STATUS_BAR_UPDATER_FRAGMENT).commitAllowingStateLoss();
        } else {
            // Google poses new restriction recently. A fragment need to have same fragment
            // manager as StatusBarUpdaterFragment, in order to become its target fragment. It
            // is OK not to call setTargetFragment. Although you may get null from
            // statusBarUpdaterFragment.getTargetFragment, during onResume,
            // statusBarUpdaterFragment.getTargetFragment will magically return correct fragment.

            //statusBarUpdaterFragment.setTargetFragment(this, 0);
        }
    }

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

        ...

        // This code block might not be necessary. Just to be safe.
        if (statusBarUpdaterFragment != null) {
            // Google poses new restriction recently. A fragment need to have same fragment
            // manager as StatusBarUpdaterFragment, in order to become its target fragment. It
            // is OK not to call setTargetFragment. Although you may get null from
            // statusBarUpdaterFragment.getTargetFragment, during onResume,
            // statusBarUpdaterFragment.getTargetFragment will magically return correct fragment.

            try {
                statusBarUpdaterFragment.setTargetFragment(this, 0);
            } catch (java.lang.IllegalArgumentException e) {
                // Shouldn't happen. Just to be safe.
                Log.e(TAG, "", e);
            }
        }