CALayer响应点击事件

我们知道CALayer不能直接响应任何响应链事件，所以不能直接处理点击事件。但是依然有两种方法可以帮助我们实现捕捉并且处理CALayer的点击事件。

方法一、convertPoint:

@interface ViewController ()

@property (nonatomic, strong) CALayer *redLayer;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
        
    self.redLayer = [CALayer layer];
    self.redLayer.frame = CGRectMake(100, 100, 100, 100);
    self.redLayer.backgroundColor = [UIColor redColor].CGColor;
    [self.view.layer addSublayer:self.redLayer];
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
    CGPoint point = [[touches anyObject] locationInView:self.view];
    CGPoint redPoint = [self.redLayer convertPoint:point fromLayer:self.view.layer];
    if ([self.redLayer containsPoint:redPoint]) {
        UIAlertController * alert = [UIAlertController alertControllerWithTitle:@"标题" message:@"红色" preferredStyle:UIAlertControllerStyleAlert];
        UIAlertAction * action = [UIAlertAction actionWithTitle:@"确定" style:UIAlertActionStyleDefault handler:nil];
        [alert addAction:action];
        [self presentViewController:alert animated:YES completion:nil];
    }
}

首先使用locationInView方法获取到点击在view上的坐标。convertPoint: fromLayer :方法传入一个CGPoint来转换坐标系，将在其父图层上的坐标转换为相对于图层自身的坐标，这样转换坐标系的方法还有以下几个：

- (CGPoint)convertPoint:(CGPoint)point fromLayer:(CALayer *)layer; 
- (CGPoint)convertPoint:(CGPoint)point toLayer:(CALayer *)layer; 
- (CGRect)convertRect:(CGRect)rect fromLayer:(CALayer *)layer;
- (CGRect)convertRect:(CGRect)rect toLayer:(CALayer *)layer;

得到触摸点相对于图层自身的坐标之后，调用containsPoint:方法。containsPoint:方法传入一个CGPoint类型参数，如果这个点在图层的frame内，则返回YES，否则返回NO。这样，就实现了对CALayer点击事件的处理。

方法二、hitTest:

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
    CGPoint point = [[touches anyObject] locationInView:self.view];
    CALayer *layer = [self.view.layer hitTest:point];
    if (layer == self.redLayer) {
        UIAlertController * alert = [UIAlertController alertControllerWithTitle:@"标题" message:@"红色" preferredStyle:UIAlertControllerStyleAlert];
        UIAlertAction * action = [UIAlertAction actionWithTitle:@"确定" style:UIAlertActionStyleDefault handler:nil];
        [alert addAction:action];
        [self presentViewController:alert animated:YES completion:nil];
    }
}

hitTest:同样传入一个CGPoint类型参数，但它的返回值不是BOOL类型，而是图层本身。如果点击的位置在最外层图层之外，则返回nil。
使用hitTest:时有一点需要注意：hitTest:返回的顺序严格按照图层树的图层顺序。