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

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);  }}

You do this by implementing View#onSaveInstanceState and View#onRestoreInstanceState and extending the View.BaseSavedState class.

public class CustomView extends View {  private int stateToSave;  ...  @Override  public Parcelable onSaveInstanceState() {    //begin boilerplate code that allows parent classes to save state    Parcelable superState = super.onSaveInstanceState();    SavedState ss = new SavedState(superState);    //end    ss.stateToSave = this.stateToSave;    return ss;  }  @Override  public void onRestoreInstanceState(Parcelable state) {    //begin boilerplate code so parent classes can restore state    if(!(state instanceof SavedState)) {      super.onRestoreInstanceState(state);      return;    }    SavedState ss = (SavedState)state;    super.onRestoreInstanceState(ss.getSuperState());    //end    this.stateToSave = ss.stateToSave;  }  static class SavedState extends BaseSavedState {    int stateToSave;    SavedState(Parcelable superState) {      super(superState);    }    private SavedState(Parcel in) {      super(in);      this.stateToSave = in.readInt();    }    @Override    public void writeToParcel(Parcel out, int flags) {      super.writeToParcel(out, flags);      out.writeInt(this.stateToSave);    }    //required field that makes Parcelables from a Parcel    public static final Parcelable.Creator<SavedState> CREATOR =        new Parcelable.Creator<SavedState>() {          public SavedState createFromParcel(Parcel in) {            return new SavedState(in);          }          public SavedState[] newArray(int size) {            return new SavedState[size];          }    };  }}

The work is split between the View and the View's SavedState class. You should do all the work of reading and writing to and from the Parcel in the SavedState class. Then your View class can do the work of extracting the state members and doing the work necessary to get the class back to a valid state.

Notes: View#onSavedInstanceState and View#onRestoreInstanceState are called automatically for you if View#getId returns a value >= 0. This happens when you give it an id in xml or call setId manually. Otherwise you have to call View#onSaveInstanceState and write the Parcelable returned to the parcel you get in Activity#onSaveInstanceState to save the state and subsequently read it and pass it to View#onRestoreInstanceState from Activity#onRestoreInstanceState.

Another simple example of this is the CompoundButton

Here is another variant that uses a mix of the two above methods.Combining the speed and correctness of Parcelable with the simplicity of a Bundle:

@Overridepublic Parcelable onSaveInstanceState() {    Bundle bundle = new Bundle();    // The vars you want to save - in this instance a string and a boolean    String someString = "something";    boolean someBoolean = true;    State state = new State(super.onSaveInstanceState(), someString, someBoolean);    bundle.putParcelable(State.STATE, state);    return bundle;}@Overridepublic void onRestoreInstanceState(Parcelable state) {    if (state instanceof Bundle) {        Bundle bundle = (Bundle) state;        State customViewState = (State) bundle.getParcelable(State.STATE);        // The vars you saved - do whatever you want with them        String someString = customViewState.getText();        boolean someBoolean = customViewState.isSomethingShowing());        super.onRestoreInstanceState(customViewState.getSuperState());        return;    }    // Stops a bug with the wrong state being passed to the super    super.onRestoreInstanceState(BaseSavedState.EMPTY_STATE); }protected static class State extends BaseSavedState {    protected static final String STATE = "YourCustomView.STATE";    private final String someText;    private final boolean somethingShowing;    public State(Parcelable superState, String someText, boolean somethingShowing) {        super(superState);        this.someText = someText;        this.somethingShowing = somethingShowing;    }    public String getText(){        return this.someText;    }    public boolean isSomethingShowing(){        return this.somethingShowing;    }}