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Android Animations and Transitions The Transitions Framework Transitioning Back and Forth

In the Activity below, we want to enable a transition back and forth between two scenes when a button is clicked. Note t

how do I fix this error

public class MainActivity extends Activity {

    protected TransitionManager mTransitionManager;
    protected Scene mScene1;
    protected Scene mScene2;
    protected Scene mCurrentScene;
    protected TransitionSet mForwardSet;
    protected TransitionSet mBackwardSet;

    // Some code omitted for brevity

    public void onButtonClicked(View view) {
        if (mCurrentScene == mScene2) {   
            mCurrentScene = mScene1;
        else {
            mCurrentScene = mScene2;



    protected void setupTransitions() {
        // These methods are setting up scenes and transitions sets like in the video

      TransitionManager transition = new TransitionManager();  // Start here!
      mTransitionManager.setTransition(mScene1, mScene2, mForwardSet);
      mTransitionManager.setTransition(mScene2, mScene1, mBackwardSet);