在 iOS 7 及更高版本中，通常会使用关键帧动画来实现此效果。
例如，一个两秒的动画序列由四个独立的动画组成，每个动画占整个动画的 25%，如下所示：
[UIView animateKeyframesWithDuration:2.0 delay:0.0 options:UIViewKeyframeAnimationOptionRepeat animations:^{
[UIView addKeyframeWithRelativeStartTime:0.00 relativeDuration:0.25 animations:^{
viewToAnimate.frame = ...;
}];
[UIView addKeyframeWithRelativeStartTime:0.25 relativeDuration:0.25 animations:^{
viewToAnimate.frame = ...;
}];
[UIView addKeyframeWithRelativeStartTime:0.50 relativeDuration:0.25 animations:^{
viewToAnimate.frame = ...;
}];
[UIView addKeyframeWithRelativeStartTime:0.75 relativeDuration:0.25 animations:^{
viewToAnimate.frame = ...;
}];
} completion:nil];
在早期的 iOS 版本中，您可以通过多种方式排列一系列动画，但我建议您避免在主线程上使用信号量。
一种方法是将动画包装在并发NSOperation子类中，直到动画完成后才会完成。然后，您可以将动画添加到您自己的自定义串行队列中：
NSOperationQueue *animationQueue = [[NSOperationQueue alloc] init];
animationQueue.maxConcurrentOperationCount = 1;
[animationQueue addOperation:[[AnimationOperation alloc] initWithDuration:1.0 delay:0.0 options:0 animations:^{
viewToAnimate.center = point1;
}]];
[animationQueue addOperation:[[AnimationOperation alloc] initWithDuration:1.0 delay:0.0 options:0 animations:^{
viewToAnimate.center = point2;
}]];
[animationQueue addOperation:[[AnimationOperation alloc] initWithDuration:1.0 delay:0.0 options:0 animations:^{
viewToAnimate.center = point3;
}]];
[animationQueue addOperation:[[AnimationOperation alloc] initWithDuration:1.0 delay:0.0 options:0 animations:^{
viewToAnimate.center = point4;
}]];
子类AnimationOperation可能如下所示：
// AnimationOperation.h
#import <Foundation/Foundation.h>
@interface AnimationOperation : NSOperation
- (instancetype)initWithDuration:(NSTimeInterval)duration delay:(NSTimeInterval)delay options:(UIViewAnimationOptions)options animations:(void (^)(void))animations;
@end
和
// AnimationOperation.m
#import "AnimationOperation.h"
@interface AnimationOperation ()
@property (nonatomic, readwrite, getter = isFinished) BOOL finished;
@property (nonatomic, readwrite, getter = isExecuting) BOOL executing;
@property (nonatomic, copy) void (^animations)(void);
@property (nonatomic) UIViewAnimationOptions options;
@property (nonatomic) NSTimeInterval duration;
@property (nonatomic) NSTimeInterval delay;
@end
@implementation AnimationOperation
@synthesize finished = _finished;
@synthesize executing = _executing;
- (instancetype)initWithDuration:(NSTimeInterval)duration delay:(NSTimeInterval)delay options:(UIViewAnimationOptions)options animations:(void (^)(void))animations {
self = [super init];
if (self) {
_animations = animations;
_options = options;
_delay = delay;
_duration = duration;
}
return self;
}
- (void)start {
if ([self isCancelled]) {
self.finished = YES;
return;
}
self.executing = YES;
[self main];
}
- (void)main {
dispatch_async(dispatch_get_main_queue(), ^{
[UIView animateWithDuration:self.duration delay:self.delay options:self.options animations:self.animations completion:^(BOOL finished) {
[self completeOperation];
}];
});
}
#pragma mark - NSOperation methods
- (void)completeOperation {
if (self.isExecuting) self.executing = NO;
if (!self.isFinished) self.finished = YES;
}
- (BOOL)isAsynchronous {
return YES;
}
- (BOOL)isExecuting {
@synchronized(self) { return _executing; }
}
- (BOOL)isFinished {
@synchronized(self) { return _finished; }
}
- (void)setExecuting:(BOOL)executing {
if (_executing != executing) {
[self willChangeValueForKey:@"isExecuting"];
@synchronized(self) { _executing = executing; }
[self didChangeValueForKey:@"isExecuting"];
}
}
- (void)setFinished:(BOOL)finished {
if (_finished != finished) {
[self willChangeValueForKey:@"isFinished"];
@synchronized(self) { _finished = finished; }
[self didChangeValueForKey:@"isFinished"];
}
}
@end
在上面的演示中，我使用了串行队列。但是您也可以使用并发队列，但使用NSOperation依赖项来管理各种动画操作之间的关系。这里有很多选择。
如果要取消动画，则可以执行以下操作：
CALayer *layer = [viewToAnimate.layer presentationLayer];
CGRect frame = layer.frame; // identify where it is now
[animationQueue cancelAllOperations]; // cancel the operations
[viewToAnimate.layer removeAllAnimations]; // cancel the animations
viewToAnimate.frame = frame; // set the final position to where it currently is
如果需要，您也可以将其合并到cancel操作中的自定义方法中。