Custom Viewgroup: onSaveInstanceState - onRestoreInstanceState http://trickyandroid.com/saving-android-view-state-correctly/

CustomLayout.java

public class CustomLayout extends LinearLayout {

  @SuppressWarnings("unchecked") @Override public Parcelable onSaveInstanceState() {
    Parcelable saveInstanceState = super.onSaveInstanceState();
    SavedState savedState = new SavedState(saveInstanceState);
    savedState.childrenStates = new SparseArray();
    for (int i = 0; i < getChildCount(); i++) {
      getChildAt(i).saveHierarchyState(savedState.childrenStates);
    }
    return savedState;
  }

  @SuppressWarnings("unchecked") @Override public void onRestoreInstanceState(Parcelable state) {
    SavedState savedState = (SavedState) state;
    super.onRestoreInstanceState(savedState.getSuperState());
    for (int i = 0; i < getChildCount(); i++) {
      getChildAt(i).restoreHierarchyState(savedState.childrenStates);
    }
  }

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

  @Override protected void dispatchRestoreInstanceState(SparseArray<Parcelable> container) {
    dispatchThawSelfOnly(container);
  }
  
  private static class SavedState extends BaseSavedState {
    private SparseArray childrenStates;

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

    private SavedState(Parcel in, ClassLoader classLoader) {
      super(in);
      childrenStates = in.readSparseArray(classLoader);
    }

    @SuppressWarnings("unchecked") @Override public void writeToParcel(Parcel out, int flags) {
      super.writeToParcel(out, flags);
      out.writeSparseArray(childrenStates);
    }

    public static final ClassLoaderCreator<SavedState> CREATOR = new ClassLoaderCreator<SavedState>() {
      @Override public SavedState createFromParcel(Parcel source, ClassLoader loader) {
        return new SavedState(source, loader);
      }

      @Override public SavedState createFromParcel(Parcel source) {
        return createFromParcel(null);
      }

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

For those who use IcePick, you can use this. This does the same thing as above but lil less ceremony

import android.os.Parcel;
import android.os.Parcelable;
import android.util.SparseArray;
import android.view.ViewGroup;
import android.widget.LinearLayout;

import icepick.State;

import static icepick.Icepick.restoreInstanceState;
import static icepick.Icepick.saveInstanceState;

class Util {
  private Util() {}

  public static SparseArray saveChildViewStates(ViewGroup viewGroup) {
    SparseArray childViewStates = new SparseArray();
    for (int i = 0; i < viewGroup.getChildCount(); i++) {
      //noinspection unchecked
      viewGroup.getChildAt(i).saveHierarchyState(childViewStates);
    }
    return childViewStates;
  }

  public static void restoreChildViewStates(ViewGroup viewGroup, SparseArray childViewStates) {
    for (int i = 0; i < viewGroup.getChildCount(); i++) {
      //noinspection unchecked
      viewGroup.getChildAt(i).restoreHierarchyState(childViewStates);
    }
  }
}

public class CustomLayout extends LinearLayout {

  @State
  MyCustomParcellable myInternalState;

  @State
  int additionalState;

  @State
  SparseArray childViewStates;

  @Override
  public Parcelable onSaveInstanceState() {
    childViewStates = Util.saveChildViewStates(this);
    return saveInstanceState(this, super.onSaveInstanceState());
  }

  @Override
  public void onRestoreInstanceState(Parcelable state) {
    super.onRestoreInstanceState(restoreInstanceState(this, state));
    Util.restoreChildViewStates(this, childViewStates);
    childViewStates = null;
  }

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

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

}

class MyCustomParcellable implements Parcelable {
  // lot of properties & parcellable implementation; use android studio extension (Android Parcelable Generator) to generate parcellable implementation
}