CADisplayLink 失效后无法停止答案

【问题标题】：CADisplayLink can't stop after invalidatedCADisplayLink 失效后无法停止
【发布时间】：2016-01-03 17:54:45
【问题描述】：

我有两个UIButton，第一个按钮将触发CustomeView 的- beginAnimation，另一个按钮将触发- endAnimation。当我依次快速按下这两个按钮时，例如begin -> end -> begin -> end -> begin -> end，我发现CADisplayLink 无法停止。更何况- rotate的射速超过了60fps，变成了60 -> 120 -> 180，就像我的主RunLoop里有不止一个CADisplaylink一样，有没有办法解决呢？而且我需要在视图的 alpha 变为零之前保持CADisplaylink 运行，所以我将[self.displayLink invalidate]; 放在完成块中，也许这会导致这个问题？

@interface CustomeView : UIView
@end

@implementation CustomeView

- (void)beginAnimation // triggered by a UIButton
{
    [UIView animateWithDuration:0.5 animations:^{ self.alpha = 1.0; }];
    self.displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(rotate)];
    [self.displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
}

- (void)endAnimation // triggered by another UIButton
{
    [UIView animateWithDuration:0.5 animations:^{ self.alpha = 0.0; } completion:^(BOOL finished) {
        [self.displayLink invalidate];
    }];
}

- (void)rotate
{
    // ....
}

【问题讨论】：

标签： ios cadisplaylink

【解决方案1】：

如果您在-endAnimation 中的完成块运行之前调用-beginAnimation（即在0.5 秒动画完成之前），您将用新的self.displayLink 覆盖旧的self.displayLink。之后，当完成块运行时，您将使新的显示链接失效，而不是旧的。

使用一个中间变量来捕获self.displayLink 的值，该值包含您要失效的显示链接。另外，为了更好地衡量，在完成后将 self.displayLink 设置为 nil。

- (void)beginAnimation // triggered by a UIButton
{
    [UIView animateWithDuration:0.5 animations:^{ self.alpha = 1.0; }];

    if (self.displayLink != nil) {
        // You called -beginAnimation before you called -endAnimation.
        // I'm not sure if your code is doing this or not, but if it does,
        // you need to decide how to handle it.
    } else {
        // Make a new display link.
        self.displayLink = [CADisplayLink displayLinkWithTarget:self selector:@selector(rotate)];
        [self.displayLink addToRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
    }
}

- (void)endAnimation // triggered by another UIButton
{
    if (self.displayLink == nil) {
        // You called -endAnimation before -beginAnimation.
        // Again, you need to determine what, if anything,
        // to do in this case.
    } else {
        CADisplayLink oldDisplayLink = self.displayLink;
        self.displayLink = nil;

        [UIView animateWithDuration:0.5 animations:^{ self.alpha = 0.0; } completion:^(BOOL finished) {
            [oldDisplayLink invalidate];
        }];
    }
}

【讨论】：