Restart animations or stop animating in some corner cases

MONActivityIndicatorViewDemo/MONActivityIndicatorViewDemo/Source/Views/MONActivityIndicatorView/MONActivityIndicatorView.h

@@ -37,6 +37,8 @@ FOUNDATION_EXPORT const unsigned char MONActivityIndicatorViewVersionString[];
 /** The assigned delegate */
 @property (weak, nonatomic) id<MONActivityIndicatorViewDelegate> delegate;
 
+/** Indicates whether the activity indicator view is animating. */
+@property (readonly, nonatomic, getter=isAnimating) BOOL animating;
 
 /**
  Starts the animation of the activity indicator.

MONActivityIndicatorViewDemo/MONActivityIndicatorViewDemo/Source/Views/MONActivityIndicatorView/MONActivityIndicatorView.m

@@ -7,13 +7,38 @@
 #import <QuartzCore/QuartzCore.h>
 #import "MONActivityIndicatorView.h"
 
+@interface MONActivityIndicatorLayer : CALayer
+
+@property (nonatomic, weak, readonly) MONActivityIndicatorView *view;
+
+@end
+
+@implementation MONActivityIndicatorLayer
+
+- (MONActivityIndicatorView *)view {
+    return (MONActivityIndicatorView *)self.delegate;
+}
+
+- (void)removeAllAnimations {
+    [super removeAllAnimations];
+
+    // `-[UITableViewCell prepareForReuse]` and `-[UICollectionViewCell prepareForReuse]` remove all animations from
+    // child views. There is no way to restart animations automatically (as we do it in `-didMoveToWindow`).
+    // So, we have to stop animating.
+    // Note: We can't do it in `-animationDidStop:finished:` animation delegate, because the delegate method is called
+    // asynchronously.
+    [self.view stopAnimating];
+}
+
+@end
+
 @interface MONActivityIndicatorView ()
 
 /** The default color of each circle. */
 @property (strong, nonatomic) UIColor *defaultColor;
 
-/** An indicator whether the activity indicator view is animating. */
-@property (readwrite, nonatomic) BOOL isAnimating;
+/** Indicates whether the activity indicator view is animating. */
+@property (readwrite, nonatomic, getter=isAnimating) BOOL animating;
 
 /**
  Sets up default values
@@ -30,6 +55,11 @@ - (void)addCircles;
  */
 - (void)removeCircles;
 
+/**
+ Adds animations to the circle layers.
+ */
+- (void)addCircleAnimations;
+
 /**
  Creates the circle view.
  @param radius The radius of the circle.
@@ -79,14 +109,32 @@ - (id)initWithCoder:(NSCoder *)aDecoder {
 }
 
 #pragma mark -
-#pragma mark - Intrinsic Content Size
+#pragma mark - UIViews
+
++ (Class)layerClass {
+    return [MONActivityIndicatorLayer class];
+}
 
 - (CGSize)intrinsicContentSize {
     CGFloat width = (self.numberOfCircles * ((2 * self.radius) + self.internalSpacing)) - self.internalSpacing;
     CGFloat height = self.radius * 2;
     return CGSizeMake(width, height);
 }
 
+- (CGSize)sizeThatFits:(CGSize)size {
+    return self.intrinsicContentSize;
+}
+
+- (void)didMoveToWindow {
+    [super didMoveToWindow];
+
+    // Core Animation animations are removed when the view is remove from a window.
+    // So, we have to add the animations again when the view is added to a window.
+    if (self.window && self.animating) {
+        [self addCircleAnimations];
+    }
+}
+
 #pragma mark -
 #pragma mark - Private Methods
 
@@ -130,36 +178,45 @@ - (void)addCircles {
             color = [self.delegate activityIndicatorView:self circleBackgroundColorAtIndex:i];
         }
         UIView *circle = [self createCircleWithRadius:self.radius
-                                                color:(color == nil) ? self.defaultColor : color
+                                                color:color ?: self.defaultColor
                                             positionX:(i * ((2 * self.radius) + self.internalSpacing))];
-        [circle setTransform:CGAffineTransformMakeScale(0, 0)];
-        [circle.layer addAnimation:[self createAnimationWithDuration:self.duration delay:(i * self.delay)] forKey:@"scale"];
+        circle.transform = CGAffineTransformMakeScale(0, 0);
         [self addSubview:circle];
     }
+
+    if (self.window) {
+        [self addCircleAnimations];
+    }
 }
 
 - (void)removeCircles {
-    [self.subviews enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
-        [obj removeFromSuperview];
+    [self.subviews enumerateObjectsUsingBlock:^(UIView *circle, NSUInteger index, BOOL *stop) {
+        [circle removeFromSuperview];
+    }];
+}
+
+- (void)addCircleAnimations {
+    [self.subviews enumerateObjectsUsingBlock:^(UIView *circle, NSUInteger index, BOOL *stop) {
+        [circle.layer addAnimation:[self createAnimationWithDuration:self.duration delay:(index * self.delay)] forKey:@"scale"];
     }];
 }
 
 #pragma mark -
 #pragma mark - Public Methods
 
 - (void)startAnimating {
-    if (!self.isAnimating) {
+    if (!self.animating) {
         [self addCircles];
         self.hidden = NO;
-        self.isAnimating = YES;
+        self.animating = YES;
     }
 }
 
 - (void)stopAnimating {
-    if (self.isAnimating) {
+    if (self.animating) {
         [self removeCircles];
         self.hidden = YES;
-        self.isAnimating = NO;
+        self.animating = NO;
     }
 }