[Snackbar] Fix glitchy dismissal animation (#1166)

* Send correct frame when notifying observers

* Redo fix

* Remove notificationFrame arg

Author: samnm

components/Snackbar/src/private/MDCSnackbarOverlayView.m

@@ -54,11 +54,6 @@ @interface MDCSnackbarOverlayView ()
  */
 @property(nonatomic) MDCSnackbarMessageView *snackbarView;
 
-/**
- Storage for a completion block that is waiting for a CAAnimation to finish.
- */
-@property(nonatomic, copy) void (^pendingCompletionBlock)(void);
-
 /**
  The object which will notify us of changes in the keyboard position.
  */
@@ -88,6 +83,16 @@ @interface MDCSnackbarOverlayView ()
  */
 @property(nonatomic) NSTimeInterval rotationDuration;
 
+/**
+ The constraint used to pin the bottom of the snackbar to the bottom of the screen.
+ */
+@property(nonatomic) NSLayoutConstraint *snackbarOnscreenConstraint;
+
+/**
+ The constraint used to pin the top of the snackbar to the bottom of the screen.
+ */
+@property(nonatomic) NSLayoutConstraint *snackbarOffscreenConstraint;
+
 @end
 
 @implementation MDCSnackbarOverlayView
@@ -272,13 +277,26 @@ - (void)setSnackbarView:(MDCSnackbarMessageView *)snackbarView {
       }
 
       // Always pin the snackbar to the bottom of the container.
-      [container addConstraint:[NSLayoutConstraint constraintWithItem:snackbarView
-                                                            attribute:NSLayoutAttributeBottom
-                                                            relatedBy:NSLayoutRelationEqual
-                                                               toItem:container
-                                                            attribute:NSLayoutAttributeBottom
-                                                           multiplier:1.0
-                                                             constant:-bottomMargin]];
+      _snackbarOnscreenConstraint = [NSLayoutConstraint constraintWithItem:snackbarView
+                                                                 attribute:NSLayoutAttributeBottom
+                                                                 relatedBy:NSLayoutRelationEqual
+                                                                    toItem:container
+                                                                 attribute:NSLayoutAttributeBottom
+                                                                multiplier:1.0
+                                                                  constant:-bottomMargin];
+      _snackbarOnscreenConstraint.active = NO; // snackbar starts off-screen.
+      _snackbarOnscreenConstraint.priority = UILayoutPriorityDefaultHigh;
+      [container addConstraint:_snackbarOnscreenConstraint];
+
+      _snackbarOffscreenConstraint = [NSLayoutConstraint constraintWithItem:snackbarView
+                                                                  attribute:NSLayoutAttributeTop
+                                                                  relatedBy:NSLayoutRelationEqual
+                                                                     toItem:container
+                                                                  attribute:NSLayoutAttributeBottom
+                                                                 multiplier:1.0
+                                                                   constant:-bottomMargin];
+      _snackbarOffscreenConstraint.active = YES;
+      [container addConstraint:_snackbarOffscreenConstraint];
 
       // Always limit the height of the snackbar.
       [container
@@ -408,40 +426,44 @@ - (void)fadeInsnackbarView:(MDCSnackbarMessageView *)snackbarView
 #pragma mark - Slide Animation
 
 - (void)slideMessageView:(MDCSnackbarMessageView *)snackbarView
-                   fromY:(CGFloat)fromY
-                     toY:(CGFloat)toY
+                onscreen:(BOOL)onscreen
       fromContentOpacity:(CGFloat)fromContentOpacity
         toContentOpacity:(CGFloat)toContentOpacity
-       notificationFrame:(CGRect)notificationFrame
               completion:(void (^)(void))completion {
-  // Save off @c completion for when the CAAnimation completes.
-  self.pendingCompletionBlock = completion;
-
-  [CATransaction begin];
+  // Prepare to move the snackbar.
+  _snackbarOnscreenConstraint.active = onscreen;
+  _snackbarOffscreenConstraint.active = !onscreen;
+  [_containingView setNeedsUpdateConstraints];
 
-  // Move the snackbar.
-  CABasicAnimation *translationAnimation =
-      [CABasicAnimation animationWithKeyPath:@"transform.translation.y"];
-  translationAnimation.duration = MDCSnackbarTransitionDuration;
-  translationAnimation.fromValue = @(fromY);
-  translationAnimation.toValue = @(toY);
-  translationAnimation.delegate = self;
-  translationAnimation.timingFunction =
+  CAMediaTimingFunction *timingFunction =
       [CAMediaTimingFunction mdc_functionWithType:MDCAnimationTimingFunctionEaseInOut];
-
-  [snackbarView.layer addAnimation:translationAnimation forKey:@"translation"];
+  [CATransaction begin];
+  [CATransaction setAnimationTimingFunction:timingFunction];
+
+  // We use UIView animation inside a CATransaction in order to use the custom animation curve.
+  [UIView animateWithDuration:MDCSnackbarTransitionDuration
+                        delay:0
+                      options:UIViewAnimationOptionCurveEaseInOut
+                   animations:^{
+                     // Trigger snackbar animation.
+                     [_containingView layoutIfNeeded];
+                   } completion:^(BOOL finished) {
+                     if (completion) {
+                       completion();
+                     }
+                   }];
 
   [snackbarView animateContentOpacityFrom:fromContentOpacity
                                        to:toContentOpacity
-                                 duration:translationAnimation.duration
-                           timingFunction:translationAnimation.timingFunction];
+                                 duration:MDCSnackbarTransitionDuration
+                           timingFunction:timingFunction];
   [CATransaction commit];
 
   // Notify the overlay system.
-  [self notifyOverlayChangeWithFrame:notificationFrame
-                            duration:translationAnimation.duration
+  [self notifyOverlayChangeWithFrame:[self snackbarRectInScreenCoordinates]
+                            duration:MDCSnackbarTransitionDuration
                                curve:0
-                      timingFunction:translationAnimation.timingFunction];
+                      timingFunction:timingFunction];
 }
 
 - (void)slideInMessageView:(MDCSnackbarMessageView *)snackbarView
@@ -450,11 +472,9 @@ - (void)slideInMessageView:(MDCSnackbarMessageView *)snackbarView
   [self triggerSnackbarLayoutChange];
 
   [self slideMessageView:snackbarView
-                   fromY:snackbarView.bounds.size.height + [self staticBottomMargin]
-                     toY:0.0f
+                onscreen:YES
       fromContentOpacity:0
         toContentOpacity:1
-       notificationFrame:[self snackbarRectInScreenCoordinates]
               completion:completion];
 }
 
@@ -464,25 +484,12 @@ - (void)slideOutMessageView:(MDCSnackbarMessageView *)snackbarView
   [self triggerSnackbarLayoutChange];
 
   [self slideMessageView:snackbarView
-                   fromY:0.0f
-                     toY:snackbarView.bounds.size.height + [self staticBottomMargin]
+                onscreen:NO
       fromContentOpacity:1
         toContentOpacity:0
-       notificationFrame:CGRectNull
               completion:completion];
 }
 
-#pragma mark - CAAnimationDelegate
-
-- (void)animationDidStop:(CAAnimation *)anim finished:(BOOL)flag {
-  void (^block)(void) = self.pendingCompletionBlock;
-  self.pendingCompletionBlock = nil;
-
-  if (block) {
-    block();
-  }
-}
-
 #pragma mark - Keyboard Notifications
 
 - (void)updatesnackbarPositionWithKeyboardUserInfo:(NSDictionary *)userInfo {