Use Core Animation to translate the layer, rather than manipulating the view's frame

MDCSwipeToChoose/Internal/MDCGeometry.m

@@ -43,10 +43,25 @@ CGFloat MDCDegreesToRadians(const CGFloat degrees) {
 CGRect MDCCGRectExtendedOutOfBounds(const CGRect rect,
                                     const CGRect bounds,
                                     const CGPoint translation) {
+
+    if (CGPointEqualToPoint(translation, CGPointZero)) {
+        @throw [NSException exceptionWithName:NSInvalidArgumentException
+                                       reason:@"Cannot extend rect with zero translation"
+                                     userInfo:nil];
+    }
+
+    CGPoint increment = CGPointZero;
+    if (translation.x != 0) {
+        increment.x = (translation.x < 0) ? -1 : 1;
+    }
+    if (translation.y != 0) {
+        increment.y = (translation.y < 0) ? -1 : 1;
+    }
+
     CGRect destination = rect;
     while (!CGRectIsNull(CGRectIntersection(bounds, destination))) {
-        destination = CGRectMake(CGRectGetMinX(destination) + translation.x,
-                                 CGRectGetMinY(destination) + translation.y,
+        destination = CGRectMake(CGRectGetMinX(destination) + increment.x,
+                                 CGRectGetMinY(destination) + increment.y,
                                  CGRectGetWidth(destination),
                                  CGRectGetHeight(destination));
     }

MDCSwipeToChoose/Internal/State/MDCViewState.h

@@ -30,11 +30,8 @@ extern const MDCRotationDirection MDCRotationTowardsCenter;
 
 @interface MDCViewState : NSObject
 
-/*!
- * The center of the view when the pan gesture began.
- */
-@property (nonatomic, assign) CGPoint originalCenter;
 @property (nonatomic, assign) CATransform3D originalTransform;
+@property (nonatomic, assign) CGPoint translation;
 
 /*!
  * When the pan gesture originates at the top half of the view, the view rotates

MDCSwipeToChoose/Public/Options/MDCSwipeOptions.m

@@ -51,21 +51,9 @@ - (instancetype)init {
 + (MDCSwipeToChooseOnChosenBlock)exitScreenOnChosenWithDuration:(NSTimeInterval)duration
                                                         options:(UIViewAnimationOptions)options {
     return ^(MDCSwipeResult *state) {
-        CGRect destination = MDCCGRectExtendedOutOfBounds(state.view.frame,
-                                                          state.view.superview.bounds,
-                                                          state.translation);
-        [UIView animateWithDuration:duration
-                              delay:0.0
-                            options:options
-                         animations:^{
-                             state.view.center = CGPointMake(CGRectGetMidX(destination),
-                                                             CGRectGetMidY(destination));
-                         } completion:^(BOOL finished) {
-                             if (finished) {
-                                 [state.view removeFromSuperview];
-                                 state.onCompletion();
-                             }
-                         }];
+        [state.view mdc_exitSuperviewFromCurrentTranslationWithDuration:duration
+                                                                options:options
+                                                             completion:state.onCompletion];
     };
 }
 

MDCSwipeToChoose/Public/Views/UIView+MDCSwipeToChoose.h

@@ -58,4 +58,13 @@
  */
 - (void)mdc_swipe:(MDCSwipeDirection)direction;
 
+/*!
+ * Continue animating the view in the direction it has been swiped, until
+ * it is completely out of bounds. Then remove it from the view hierarchy.
+ *
+ * This is a low-level method intended to be called as part of an onChosen block.
+ */
+- (void)mdc_exitSuperviewFromCurrentTranslationWithDuration:(NSTimeInterval)duration
+                                                    options:(UIViewAnimationOptions)options
+                                                 completion:(void(^)(void))completion;
 @end

MDCSwipeToChoose/Public/Views/UIView+MDCSwipeToChoose.m

@@ -38,8 +38,8 @@ @implementation UIView (MDCSwipeToChoose)
 - (void)mdc_swipeToChooseSetup:(MDCSwipeOptions *)options {
     self.mdc_options = options ? options : [MDCSwipeOptions new];
     self.mdc_viewState = [MDCViewState new];
-    self.mdc_viewState.originalCenter = self.center;
     self.mdc_viewState.originalTransform = self.layer.transform;
+    self.mdc_viewState.translation = CGPointZero;
 
     if (options.swipeEnabled) {
         [self mdc_setupPanGestureRecognizer];
@@ -60,9 +60,10 @@ - (void)mdc_swipe:(MDCSwipeDirection)direction {
     void (^animations)(void) = ^{
         CGPoint translation = [self mdc_translationExceedingThreshold:self.mdc_options.threshold
                                                             direction:direction];
-        self.center = MDCCGPointAdd(self.center, translation);
-        [self mdc_rotateForTranslation:translation
-                     rotationDirection:MDCRotationAwayFromCenter];
+
+        self.mdc_viewState.translation = translation;
+        self.mdc_viewState.rotationDirection = MDCRotationAwayFromCenter;
+        [self mdc_applyLayerTransform];
         [self mdc_executeOnPanBlockForTranslation:translation];
     };
 
@@ -78,6 +79,39 @@ - (void)mdc_swipe:(MDCSwipeDirection)direction {
                      completion:completion];
 }
 
+- (void)mdc_exitSuperviewFromCurrentTranslationWithDuration:(NSTimeInterval)duration
+                                                    options:(UIViewAnimationOptions)options
+                                                 completion:(void(^)(void))completion
+{
+    CGPoint translation = self.mdc_viewState.translation;
+    if (translation.x == 0) {
+        return;
+    }
+
+    //We aren't supposed to access self.frame while a transform is active
+    CGSize size = self.bounds.size;
+    CGRect currentRect = CGRectMake(self.center.x - (size.width/2), self.center.y - (size.height/2),
+                                    size.width, size.height);
+
+    CGRect destination = MDCCGRectExtendedOutOfBounds(currentRect,
+                                                      self.superview.bounds,
+                                                      translation);
+    CGPoint difference = MDCCGPointSubtract(destination.origin, currentRect.origin);
+    self.mdc_viewState.translation = MDCCGPointAdd(translation, difference);
+
+    [UIView animateWithDuration:duration
+                          delay:0.0
+                        options:options
+                     animations:^{
+                         [self mdc_applyLayerTransform];
+                     } completion:^(BOOL finished) {
+                         if (finished) {
+                             [self removeFromSuperview];
+                             completion();
+                         }
+                     }];
+}
+
 #pragma mark - Internal Methods
 
 - (void)setMdc_options:(MDCSwipeOptions *)options {
@@ -123,9 +157,7 @@ - (void)mdc_finalizePositionForDirection:(MDCSwipeDirection)direction {
     switch (direction) {
         case MDCSwipeDirectionRight:
         case MDCSwipeDirectionLeft: {
-            CGPoint translation = MDCCGPointSubtract(self.center,
-                                                     self.mdc_viewState.originalCenter);
-            [self mdc_exitSuperviewFromTranslation:translation];
+            [self mdc_exitSuperviewFromTranslation:self.mdc_viewState.translation];
             break;
         }
         case MDCSwipeDirectionNone:
@@ -141,7 +173,6 @@ - (void)mdc_returnToOriginalCenter {
                         options:self.mdc_options.swipeCancelledAnimationOptions
                      animations:^{
                          self.layer.transform = self.mdc_viewState.originalTransform;
-                         self.center = self.mdc_viewState.originalCenter;
                      } completion:^(BOOL finished) {
                          id<MDCSwipeToChooseDelegate> delegate = self.mdc_options.delegate;
                          if ([delegate respondsToSelector:@selector(viewDidCancelSwipe:)]) {
@@ -153,24 +184,27 @@ - (void)mdc_returnToOriginalCenter {
 - (void)mdc_exitSuperviewFromTranslation:(CGPoint)translation {
     MDCSwipeDirection direction = [self mdc_directionOfExceededThreshold];
     id<MDCSwipeToChooseDelegate> delegate = self.mdc_options.delegate;
+    void (^onChoose)(void) = ^ {
+        MDCSwipeResult *state = [MDCSwipeResult new];
+        state.view = self;
+        state.translation = translation;
+        state.direction = direction;
+        state.onCompletion = ^{
+            if ([delegate respondsToSelector:@selector(view:wasChosenWithDirection:)]) {
+                [delegate view:self wasChosenWithDirection:direction];
+            }
+        };
+        self.mdc_options.onChosen(state);
+    };
     if ([delegate respondsToSelector:@selector(view:shouldBeChosenWithDirection:yes:no:)]) {
-        [delegate view:self shouldBeChosenWithDirection:direction yes:^{
-            MDCSwipeResult *state = [MDCSwipeResult new];
-            state.view = self;
-            state.translation = translation;
-            state.direction = direction;
-            state.onCompletion = ^{
-                if ([delegate respondsToSelector:@selector(view:wasChosenWithDirection:)]) {
-                    [delegate view:self wasChosenWithDirection:direction];
-                }
-            };
-            self.mdc_options.onChosen(state);
-        } no:^{
+        [delegate view:self shouldBeChosenWithDirection:direction yes:onChoose no:^{
             [self mdc_returnToOriginalCenter];
             if (self.mdc_options.onCancel != nil){
                 self.mdc_options.onCancel(self);
             }
         }];
+    } else {
+        onChoose();
     }
 }
 
@@ -193,12 +227,16 @@ - (void)mdc_executeOnPanBlockForTranslation:(CGPoint)translation {
     }
 }
 
-#pragma mark Rotation
-
-- (void)mdc_rotateForTranslation:(CGPoint)translation
-               rotationDirection:(MDCRotationDirection)rotationDirection {
+- (void)mdc_applyLayerTransform {
+    CATransform3D t = self.mdc_viewState.originalTransform;
+
+    CGPoint translation = self.mdc_viewState.translation;
+    t = CATransform3DTranslate(t, translation.x, translation.y, 0);
+
     CGFloat rotation = MDCDegreesToRadians(translation.x/100 * self.mdc_options.rotationFactor);
-    self.layer.transform = CATransform3DMakeRotation(rotationDirection * rotation, 0.0, 0.0, 1.0);
+    t = CATransform3DRotate(t, self.mdc_viewState.rotationDirection * rotation, 0, 0, 1);
+
+    self.layer.transform = t;
 }
 
 #pragma mark Threshold
@@ -221,9 +259,9 @@ - (CGPoint)mdc_translationExceedingThreshold:(CGFloat)threshold
 }
 
 - (MDCSwipeDirection)mdc_directionOfExceededThreshold {
-    if (self.center.x > self.mdc_viewState.originalCenter.x + self.mdc_options.threshold) {
+    if (self.mdc_viewState.translation.x > self.mdc_options.threshold) {
         return MDCSwipeDirectionRight;
-    } else if (self.center.x < self.mdc_viewState.originalCenter.x - self.mdc_options.threshold) {
+    } else if (self.mdc_viewState.translation.x < -self.mdc_options.threshold) {
         return MDCSwipeDirectionLeft;
     } else {
         return MDCSwipeDirectionNone;
@@ -236,8 +274,8 @@ - (void)mdc_onSwipeToChoosePanGestureRecognizer:(UIPanGestureRecognizer *)panGes
     UIView *view = panGestureRecognizer.view;
 
     if (panGestureRecognizer.state == UIGestureRecognizerStateBegan) {
-        self.mdc_viewState.originalCenter = view.center;
         self.mdc_viewState.originalTransform = view.layer.transform;
+        self.mdc_viewState.translation = CGPointZero;
 
         // If the pan gesture originated at the top half of the view, rotate the view
         // away from the center. Otherwise, rotate towards the center.
@@ -254,11 +292,9 @@ - (void)mdc_onSwipeToChoosePanGestureRecognizer:(UIPanGestureRecognizer *)panGes
     } else {
         // Update the position and transform. Then, notify any listeners of
         // the updates via the pan block.
-        CGPoint translation = [panGestureRecognizer translationInView:view];
-        view.center = MDCCGPointAdd(self.mdc_viewState.originalCenter, translation);
-        [self mdc_rotateForTranslation:translation
-                     rotationDirection:self.mdc_viewState.rotationDirection];
-        [self mdc_executeOnPanBlockForTranslation:translation];
+        self.mdc_viewState.translation = [panGestureRecognizer translationInView:view];
+        [self mdc_applyLayerTransform];
+        [self mdc_executeOnPanBlockForTranslation:self.mdc_viewState.translation];
     }
 }