How to prevent custom views from losing state across screen orientation changes

Question

I\'ve successfully implemented onRetainNonConfigurationInstance() for my main Activity to save and restore certain critical components across screen orientation

Answer 1

I found that this answer was causing some crashes on Android versions 9 and 10. I think it's a good approach but when I was looking at some Android code I found out it was missing a constructor. The answer is quite old so at the time there probably was no need for it. When I added the missing constructor and called it from the creator the crash was fixed.

So here is the edited code:

public class CustomView extends View {

    private int stateToSave;

    ...

    @Override
    public Parcelable onSaveInstanceState() {
        Parcelable superState = super.onSaveInstanceState();
        SavedState ss = new SavedState(superState);

        // your custom state
        ss.stateToSave = this.stateToSave;

        return ss;
    }

    @Override
    protected void dispatchSaveInstanceState(SparseArray container)
    {
        dispatchFreezeSelfOnly(container);
    }

    @Override
    public void onRestoreInstanceState(Parcelable state) {
        SavedState ss = (SavedState) state;
        super.onRestoreInstanceState(ss.getSuperState());

        // your custom state
        this.stateToSave = ss.stateToSave;
    }

    @Override
    protected void dispatchRestoreInstanceState(SparseArray container)
    {
        dispatchThawSelfOnly(container);
    }

    static class SavedState extends BaseSavedState {
        int stateToSave;

        SavedState(Parcelable superState) {
            super(superState);
        }

        private SavedState(Parcel in) {
            super(in);
            this.stateToSave = in.readInt();
        }

        // This was the missing constructor
        @RequiresApi(Build.VERSION_CODES.N)
        SavedState(Parcel in, ClassLoader loader)
        {
            super(in, loader);
            this.stateToSave = in.readInt();
        }

        @Override
        public void writeToParcel(Parcel out, int flags) {
            super.writeToParcel(out, flags);
            out.writeInt(this.stateToSave);
        }    

        public static final Creator CREATOR =
            new ClassLoaderCreator() {

            // This was also missing
            @Override
            public SavedState createFromParcel(Parcel in, ClassLoader loader)
            {
                return Build.VERSION.SDK_INT >= Build.VERSION_CODES.N ? new SavedState(in, loader) : new SavedState(in);
            }

            @Override
            public SavedState createFromParcel(Parcel in) {
                return new SavedState(in, null);
            }

            @Override
            public SavedState[] newArray(int size) {
                return new SavedState[size];
            }
        };
    }
}