Fragment must be a public static class to be properly recreated from instance state

Question

After updating to the latest support repository,

compile 'com.android.support:appcompat-v7:24.2.0'
compile 'com.android.support:design:24.2.0'
compile 'com.android.support:percent:24.2.0'
compile 'com.android.support:recyclerview-v7:24.2.0'

I'm getting the weird exception.

java.lang.IllegalStateException: Fragment null must be a public static class to be  properly recreated from instance state.
at android.support.v4.app.BackStackRecord.doAddOp(BackStackRecord.java:435)
at android.support.v4.app.BackStackRecord.add(BackStackRecord.java:414)
at android.support.v4.app.DialogFragment.show(DialogFragment.java:154)
at com.androidapp.base.BaseActivity.showDialogFragment(BaseActivity.java:78)
at com.androidapp.MainActivity.showNewDialog(MainActivity.java:304)
at com.androidapp.MainActivity$6.onClick(MainActivity.java:228)

In my BaseActivity class, I've created a re-usable fragment which can be used in activity class that extends the BaseActivty

public void showDialogFragment(DialogFragment newFragment) {
        FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
        Fragment prev = getSupportFragmentManager().findFragmentByTag("dialog");
        if (prev != null) {
            ft.remove(prev);
        }
        ft.addToBackStack("dialog");
        newFragment.show(ft, "dialog");
    }

Back to the MainActivty I've used the fragment like this,

public class MainActivity extends BaseActivity {

    @SuppressLint("ValidFragment")
        public void showNewDialog(int type, String title, String message) {
            final DialogNew dialog = new DialogNew() {
                @Override
                public void success(boolean isLandscape) {
                    .......
                }

                @Override
                public void cancel() {

                }
            };
            dialog.setArgs(title, message);
            super.showDialogFragment(dialog);
        }
}

The DialogNew class is below,

public abstract class DialogNew extends DialogFragment {

    private View rootView;

    private String title;
    private String message;

    public void setArgs(String title, String message) {
        Bundle args = new Bundle();
        args.putString("title", title);
        args.putString("message", message);
        setArguments(args);
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setStyle(STYLE_NO_TITLE, 0);
    }

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

        rootView = inflater.inflate(R.layout.fragment_new_dialog, container, false);

        init();
        setListeners();

        return rootView;
    }

    public abstract void success(boolean isLandscape);

    public abstract void cancel();
}

PS: The same code works with older support repository.

Solution 1

The error is not especially weird. If you were not getting this error before, that was weird.

Android destroys and recreates fragments as part of a configuration change (e.g., screen rotation) and as part of rebuilding a task if needed (e.g., user switches to another app, your app's process is terminated while it is in the background, then the user tries to return to your app, all within 30 minutes or so). Android has no means of recreating an anonymous subclass of DialogNew.

So, make a regular public Java class (or a public static nested class) that extends DialogNew and has your business logic, replacing the anonymous subclass of DialogNew that you are using presently.

Solution 2

I recreated my fragment from scratch, it's solved the problem for me.

New -> Fragment -> Fragment (Blank) and you uncheck the 2nd box before confirming.

Solution 3

Edit: You probably don't want to do this... See the comments.

The code sample looks similar to what I had suggested over here, and I also recently discovered that the solution I had there was not working anymore. I've updated my answer there for Java7, but if you have Java8 the solution is super easy:

(I haven't tested this yet)

public class DialogNew extends DialogFragment {
    private View rootView;
    private String title;
    private String message;

    // Do nothing by default
    private Consumer mSuccess = (boolean b) -> {};
    private Runnable mCancel = () -> {};

    public void setArgs(String title, String message) {
        Bundle args = new Bundle();
        args.putString("title", title);
        args.putString("message", message);
        setArguments(args);
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setStyle(STYLE_NO_TITLE, 0);
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        rootView = inflater.inflate(R.layout.fragment_new_dialog, container, false);
        // use mSuccess.accept(boolean) when needed
        init();
        setListeners();
        return rootView;
    }

    public void setSuccess(Consumer success) {
        mSuccess = success;
    }

    public void setCancel(Runnable cancel) {
        mCancel = cancel;
    }
}

Then in the Main activity:

public class MainActivity extends BaseActivity {
        public void showNewDialog(int type, String title, String message) {
            final DialogNew dialog = new DialogNew();
            dialog.setArgs(title, message);
            dialog.setSuccess((boolean isLandscape) -> {
                //....
            });
            super.showDialogFragment(dialog);
        }
}

Solution 4

The reason for this error is very well explained on Android Developers guides.

When the system issues a configuration change, it needs to be able to create a new instance of your fragment. In order to do so, it relies on a default constructor of the fragment which takes no arguments and therefore cannot have any dependencies. If your Fragment class is not a static public class, the system is unable to reflectively find this default constructor and the error indicates just that.

To get around the problem, you will have to override the default implementation of the FragmentFactory of the FragmentManager instance which will handle creation of your fragment. This is explained by code in the link I provided.

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