3.4 Hit Testing

由 xpproen 创建, 最后一次修改 2016-02-24

Hit Testing

第一章“图层树”证实了最好使用图层相关视图,而不是创建独立的图层关系。其中一个原因就是要处理额外复杂的触摸事件。

CALayer并不关心任何响应链事件,所以不能直接处理触摸事件或者手势。但是它有一系列的方法帮你处理事件:-containsPoint:-hitTest:

-containsPoint:接受一个在本图层坐标系下的CGPoint,如果这个点在图层frame范围内就返回YES。如清单3.4所示第一章的项目的另一个合适的版本,也就是使用-containsPoint:方法来判断到底是白色还是蓝色的图层被触摸了 (图3.10)。这需要把触摸坐标转换成每个图层坐标系下的坐标,结果很不方便。

清单3.4 使用containsPoint判断被点击的图层

@interface ViewController ()

@property (nonatomic, weak) IBOutlet UIView *layerView;
@property (nonatomic, weak) CALayer *blueLayer;

@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    //create sublayer
    self.blueLayer = [CALayer layer];
    self.blueLayer.frame = CGRectMake(50.0f, 50.0f, 100.0f, 100.0f);
    self.blueLayer.backgroundColor = [UIColor blueColor].CGColor;
    //add it to our view
    [self.layerView.layer addSublayer:self.blueLayer];
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    //get touch position relative to main view
    CGPoint point = [[touches anyObject] locationInView:self.view];
    //convert point to the white layer's coordinates
    point = [self.layerView.layer convertPoint:point fromLayer:self.view.layer];
    //get layer using containsPoint:
    if ([self.layerView.layer containsPoint:point]) {
        //convert point to blueLayer’s coordinates
        point = [self.blueLayer convertPoint:point fromLayer:self.layerView.layer];
        if ([self.blueLayer containsPoint:point]) {
            [[[UIAlertView alloc] initWithTitle:@"Inside Blue Layer"
                                        message:nil
                                       delegate:nil
                              cancelButtonTitle:@"OK"
                              otherButtonTitles:nil] show];
        } else {
            [[[UIAlertView alloc] initWithTitle:@"Inside White Layer"
                                        message:nil
                                       delegate:nil
                              cancelButtonTitle:@"OK"
                              otherButtonTitles:nil] show];
        }
    }
}

@end

以上内容是否对您有帮助:
二维码
建议反馈
二维码