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

To augment other answers - if you have multiple custom compound views with the same ID and they are all being restored with the state of the last view on a configuration change, all you need to do is tell the view to only dispatch save/restore events to itself by overriding a couple of methods.

class MyCompoundView : ViewGroup {

    ...

    override fun dispatchSaveInstanceState(container: SparseArray<Parcelable>) {
        dispatchFreezeSelfOnly(container)
    }

    override fun dispatchRestoreInstanceState(container: SparseArray<Parcelable>) {
        dispatchThawSelfOnly(container)
    }
}

For an explanation of what is happening and why this works, see this blog post. Basically your compound view's children's view IDs are shared by each compound view and state restoration gets confused. By only dispatching state for the compound view itself, we prevent their children from getting mixed messages from other compound views.

Answer 2

I had the problem that onRestoreInstanceState restored all my custom views with the state of the last view. I solved it by adding these two methods to my custom view:

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

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

Answer 3

I think this is a much simpler version. Bundle is a built-in type which implements Parcelable

public class CustomView extends View
{
  private int stuff; // stuff

  @Override
  public Parcelable onSaveInstanceState()
  {
    Bundle bundle = new Bundle();
    bundle.putParcelable("superState", super.onSaveInstanceState());
    bundle.putInt("stuff", this.stuff); // ... save stuff 
    return bundle;
  }

  @Override
  public void onRestoreInstanceState(Parcelable state)
  {
    if (state instanceof Bundle) // implicit null check
    {
      Bundle bundle = (Bundle) state;
      this.stuff = bundle.getInt("stuff"); // ... load stuff
      state = bundle.getParcelable("superState");
    }
    super.onRestoreInstanceState(state);
  }
}