How to dealloc a UIView while one of its subviews is animating? - ios

Question

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I am attempting to create a custom UIActivityIndicatorView. The custom view should behave the exactly the same as the standard view, except the image that it spins looks different. I noticed that my custom view would not deallocate when it is removed from its superview in the following test code:
ActivityIndicatorCustomView* v = [[ActivityIndicatorCustomView alloc] initWithFrame:CGRectMake(50.0f, 50.0f, 100.0f, 100.0f)];
[[UIApplication sharedApplication].keyWindow addSubview:v];
[v removeFromSuperview];
The culprit is the animation block, because when it is commented out, dealloc will be called. I believe it is a retain cycle, but I don't see how to solve the issue.
ActivityIndicatorCustomView.h
#import <UIKit/UIKit.h>
#interface ActivityIndicatorCustomView : UIView
#property(nonatomic, assign, readonly) BOOL isAnimating;
- (void)startAnimating;
- (void)stopAnimating;
#end
ActivityIndicatorCustomView.m
static const NSTimeInterval ANIMATION_PERIOD_HALF_LIFE = 1.0f;
#import "ActivityIndicatorCustomView.h"
#interface ActivityIndicatorCustomView ()
#property(nonatomic, strong) UIImageView* imageView;
#property(nonatomic, assign, readwrite) BOOL isAnimating;
- (void)animateWithTransform:(CGAffineTransform)transform;
#end
#implementation ActivityIndicatorCustomView
#pragma mark NSObject
- (void)dealloc
{
NSLog(#"dealloc");
}
#pragma mark UIView
- (id)initWithFrame:(CGRect)frame
{
if (self = [super initWithFrame:frame]) {
self.imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:#"activityIndicatorCustom"]];
self.imageView.frame = self.bounds;
[self addSubview:self.imageView];
}
return self;
}
- (void)didMoveToSuperview
{
if (!self.hidden && self.superview != nil) {
[self startAnimating];
}
}
- (void)willMoveToSuperview:(UIView *)newSuperview
{
if (newSuperview == nil) {
[self stopAnimating];
}
}
- (void)setHidden:(BOOL)hidden
{
if (hidden) {
[self stopAnimating];
} else if (self.superview != nil) {
[self startAnimating];
}
[super setHidden:hidden];
}
#pragma mark ActivityIndicatorCustomView
- (void)startAnimating
{
if (self.isAnimating) {
return;
}
self.isAnimating = YES;
[self animateWithTransform:CGAffineTransformMakeRotation((CGFloat)M_PI)];
}
- (void)stopAnimating
{
[self.imageView.layer removeAllAnimations];
self.isAnimating = NO;
}
#pragma mark ()
- (void)animateWithTransform:(CGAffineTransform)transform
{
// Must split the animation into two semi-circles. If
// you attempt to rotate a full circle, nothing will
// happen.
__block ActivityIndicatorCustomView* weakSelf = self;
[UIView
animateWithDuration:ANIMATION_PERIOD_HALF_LIFE
delay:0.0
options:UIViewAnimationOptionCurveLinear
animations:^{
weakSelf.imageView.transform = transform;
} completion:^(BOOL finished) {
[weakSelf animateWithTransform:CGAffineTransformIsIdentity(transform)
? CGAffineTransformMakeRotation((CGFloat)M_PI)
: CGAffineTransformIdentity
];
}
];
}
#end

Answer 1

I was following a bad tutorial on retain cycles in blocks. It told me to do
__block MyViewController *weakSelf = self;
This is wrong. To create a weak reference, I should do this instead:
__weak ActivityIndicatorCustomView* weakSelf = self;
[UIView
animateWithDuration:ANIMATION_PERIOD_HALF_LIFE
delay:0.0
options:UIViewAnimationOptionCurveLinear
animations:^{
weakSelf.imageView.transform = transform;
} completion:^(BOOL finished) {
[weakSelf animateWithTransform:CGAffineTransformIsIdentity(transform)
? CGAffineTransformMakeRotation((CGFloat)M_PI)
: CGAffineTransformIdentity
];
}
];

Answer 2

I think this is because you continue animating (and retain self in next [self animateWithTransform:] call) in the completion block. Try, for example, checking for the superview to decide whether to continue animating:
completion:^(BOOL finished) {
if (self.superview) {
[self animateWithTransform:CGAffineTransformIsIdentity(transform)
? CGAffineTransformMakeRotation((CGFloat)M_PI)
: CGAffineTransformIdentity
];
}
}