Stop using RenderNodeAnimator callbacks

Bug: 17281017

- RenderNodeAnimator's callbacks are asynchronous and thus cannot be
  relied upon for synchronus state changes. Instead use Animator#end()
  and rely on the ValueAnimator synchronously invoking the listener's
  onAnimationStart callback.
- Also to prevent future NPEs, remove mCurrentButton ivar and instead
  specify the source button directly.

Change-Id: I4ca05b46c582474a6ca7e00d8d16df118ede7eb4

src/com/android/calculator2/Calculator.java

@@ -86,7 +86,6 @@ public class Calculator extends Activity
                 case KeyEvent.KEYCODE_NUMPAD_ENTER:
                 case KeyEvent.KEYCODE_ENTER:
                     if (keyEvent.getAction() == KeyEvent.ACTION_UP) {
-                        mCurrentButton = mEqualButton;
                         onEquals();
                     }
                     // ignore all other actions
@@ -114,10 +113,9 @@ public class Calculator extends Activity
     private CalculatorEditText mResultEditText;
     private ViewPager mPadViewPager;
     private View mDeleteButton;
-    private View mEqualButton;
     private View mClearButton;
+    private View mEqualButton;
 
-    private View mCurrentButton;
     private Animator mCurrentAnimator;
 
     @Override
@@ -156,9 +154,10 @@ public class Calculator extends Activity
 
     @Override
     protected void onSaveInstanceState(@NonNull Bundle outState) {
-        // If there's an animation in progress, cancel it first to ensure our state is up-to-date.
+        // If there's an animation in progress, end it immediately to ensure the state is
+        // up-to-date before it is serialized.
         if (mCurrentAnimator != null) {
-            mCurrentAnimator.cancel();
+            mCurrentAnimator.end();
         }
 
         super.onSaveInstanceState(outState);
@@ -212,16 +211,14 @@ public class Calculator extends Activity
     public void onUserInteraction() {
         super.onUserInteraction();
 
-        // If there's an animation in progress, cancel it so the user interaction can be handled
-        // immediately.
+        // If there's an animation in progress, end it immediately to ensure the state is
+        // up-to-date before the pending user interaction is handled.
         if (mCurrentAnimator != null) {
-            mCurrentAnimator.cancel();
+            mCurrentAnimator.end();
         }
     }
 
     public void onButtonClick(View view) {
-        mCurrentButton = view;
-
         switch (view.getId()) {
             case R.id.eq:
                 onEquals();
@@ -248,8 +245,6 @@ public class Calculator extends Activity
 
     @Override
     public boolean onLongClick(View view) {
-        mCurrentButton = view;
-
         if (view.getId() == R.id.del) {
             onClear();
             return true;
@@ -348,11 +343,11 @@ public class Calculator extends Activity
                         revealCenterX, revealCenterY, 0.0f, revealRadius);
         revealAnimator.setDuration(
                 getResources().getInteger(android.R.integer.config_longAnimTime));
-        revealAnimator.addListener(listener);
 
         final Animator alphaAnimator = ObjectAnimator.ofFloat(revealView, View.ALPHA, 0.0f);
         alphaAnimator.setDuration(
                 getResources().getInteger(android.R.integer.config_mediumAnimTime));
+        alphaAnimator.addListener(listener);
 
         final AnimatorSet animatorSet = new AnimatorSet();
         animatorSet.play(revealAnimator).before(alphaAnimator);
@@ -374,9 +369,11 @@ public class Calculator extends Activity
             return;
         }
 
-        reveal(mCurrentButton, R.color.calculator_accent_color, new AnimatorListenerAdapter() {
+        final View sourceView = mClearButton.getVisibility() == View.VISIBLE
+                ? mClearButton : mDeleteButton;
+        reveal(sourceView, R.color.calculator_accent_color, new AnimatorListenerAdapter() {
             @Override
-            public void onAnimationEnd(Animator animation) {
+            public void onAnimationStart(Animator animation) {
                 mFormulaEditText.getEditableText().clear();
             }
         });
@@ -389,9 +386,9 @@ public class Calculator extends Activity
             return;
         }
 
-        reveal(mCurrentButton, R.color.calculator_error_color, new AnimatorListenerAdapter() {
+        reveal(mEqualButton, R.color.calculator_error_color, new AnimatorListenerAdapter() {
             @Override
-            public void onAnimationEnd(Animator animation) {
+            public void onAnimationStart(Animator animation) {
                 setState(CalculatorState.ERROR);
                 mResultEditText.setText(errorResourceId);
             }