在 AutoLayout 中使用 CALayer

使用 AutoLayout 时，view 不会立刻布局，而如果此时恰好需要给 view 添加 layer，layer 的 frame 设置为 view 的 frame 会得到 (0, 0)，那么如果在 AutoLayout 中设置 CALayer 的 frame 呢？

方法一

通过重写 UIView 的 + (Class)layerClass 方法，自定义 CALayer。

@implementation PlayerView
+ (Class)layerClass {
    return [AVPlayerLayer class];
}
@end

在实际中用的时候就可以直接添加

playerView = [PlayerView new];
AVPlayer *player = [[AVPlayer alloc] initWithPlayerItem:playItem];
[(AVPlayerLayer *)playerView.layer setPlayer:player];

方法二

通过 block 回调 UIView 的 layoutSubviews，这样就可以很灵活的布局 CALayer 了。

@implementation UIView (LayoutSubviewsCallback)
+ (void)load {
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Method originalMethod = class_getInstanceMethod(self, 
                                    @selector(layoutSubviews));
        Method newMethod = class_getInstanceMethod(self, 
                            @selector(ls_layoutSubviews));
        
        BOOL didAddMethod = class_addMethod(self, 
                        @selector(layoutSubviews), 
                        method_getImplementation(newMethod), 
                        method_getTypeEncoding(newMethod));
        if (didAddMethod) {
            class_replaceMethod(self, 
                @selector(ls_layoutSubviews), 
                method_getImplementation(originalMethod), 
                method_getTypeEncoding(originalMethod));
        } else {
            method_exchangeImplementations(originalMethod, newMethod);
        }
    });
}

- (void)ls_layoutSubviews {
    [self ls_layoutSubviews];
    
    if (self.layoutSubviewsCallback) {
        self.layoutSubviewsCallback(self);
    }
}

- (void)setLayoutSubviewsCallback:(void (^)(UIView *))layoutSubviewsCallback {
    objc_setAssociatedObject(self, 
                    "layoutSubviewsCallback", 
                    layoutSubviewsCallback, 
                    OBJC_ASSOCIATION_RETAIN);
}

- (void (^)(UIView *))layoutSubviewsCallback {
    return objc_getAssociatedObject(self, "layoutSubviewsCallback");
}
@end

使用时：

AVPlayerLayer *avLayer = [AVPlayerLayer new];
[playerView.layer addSublayer:avLayer];
playerView.layoutSubviewsCallback = ^(UIView *view) {
    avLayer.frame = view.bounds;
};

方法三

直接在 viewDidLayoutSubviews 中设置

- (void)viewDidLayoutSubviews {
    [super viewDidLayoutSubviews];
    avLayer.frame = playerView.frame;
}

方法四

使用 GCD，因为即使设置延迟 0 秒，GCD 的执行也会在下一个 runloop，此时 view 已经布局结束。

dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 
        (int64_t)(0 * NSEC_PER_SEC)), 
        dispatch_get_main_queue(), ^{
    avLayer.frame = playerView.frame;
});