我有一个包含 3 个独立 subview 的父 View 。 subview 在父 View 中展开，没有重叠(并且中间有一些空间)。当用户在屏幕上移动她的手指(没有抬起它)时，我想在他们进入和退出每个 subview 时跟踪触摸。

示例:如果用户开始触摸屏幕上 subview 之外的某处，然后将她的手指滑过 subview 1，离开 subview 1，再滑过 subview 2，然后松手，我会期望触发这些事件:

1. 触摸开始
2. 触摸输入的 child 1
3. 触摸退出的 child 1
4. 触摸输入的 child 2
5. 触摸结束

似乎 touchesBegan:withEvent: 和 touchesEnded:withEvent: 方法在这种情况下会有所帮助，但是当我在 subview Controller 上定义它们时，它们并没有完全按照我的意愿进行——如果用户开始在 subview 外部触摸，然后在 subview 上滑动， subview 本身不会触发任何触摸事件。

当前的解决方案:我目前使用的解决方案感觉真的很难实现。我正在观察父级上的 touchesBegan:withEvent:、touchesEnded:withEvent: 和 touchesMoved:withEvent:，获取每个事件的坐标，并确定它们是否位于子级的范围内。如果他们这样做，我会触发相应的事件，如上所述。

这种方法大部分都有效，但感觉效率很低。感觉框架应该为我处理这项工作。我的状态管理代码有时也会错过“进入”或“退出”触发器，我怀疑这是因为触摸事件要么被丢弃，要么以意外的顺序出现。我在这里错过了更好的方法吗？

最佳答案

最简单的解决方案是这样的:

- (void)viewDidLoad
{
    [super viewDidLoad];

    UIPanGestureRecognizer *pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(pan:)];
    [self.view addGestureRecognizer:pan];

    // Do any additional setup after loading the view.
}

- (void)pan:(UIPanGestureRecognizer *)sender
{
    static NSInteger startViewIndex;
    static NSInteger endViewIndex;
    CGPoint location = [sender locationInView:self.view];

    if (sender.state == UIGestureRecognizerStateBegan)
    {
        if (CGRectContainsPoint(self.view0.frame, location))
            startViewIndex = 0;
        else if (CGRectContainsPoint(self.view1.frame, location))
            startViewIndex = 1;
        else if (CGRectContainsPoint(self.view2.frame, location))
            startViewIndex = 2;
        else 
            startViewIndex = -1;
    }
    else if (sender.state == UIGestureRecognizerStateEnded)
    {
        if (CGRectContainsPoint(self.view0.frame, location))
            endViewIndex = 0;
        else if (CGRectContainsPoint(self.view1.frame, location))
            endViewIndex = 1;
        else if (CGRectContainsPoint(self.view2.frame, location))
            endViewIndex = 2;
        else 
            endViewIndex = -1;

        if (startViewIndex != -1 && endViewIndex != -1 && startViewIndex != endViewIndex)
        {
            // successfully moved between subviews!
            NSLog(@"Moved from %1d to %1d", startViewIndex, endViewIndex);
        }
    }
}

也许更优雅的方法是定义您自己的自定义手势识别器(这样，如果您不从您的 subview 之一拖动，它将失败，这将允许您可能在其他地方进行的其他手势识别器工作。 .. 可能不是问题，除非你使用多个手势识别器；它还将手势逻辑的细节与 View Controller 的其余部分隔离开来):

@interface PanBetweenSubviewsGestureRecognizer : UIPanGestureRecognizer
{
    NSMutableArray *_arrayOfFrames;
}

@property NSInteger startingIndex;
@property NSInteger endingIndex;

@end

@implementation PanBetweenSubviewsGestureRecognizer

@synthesize startingIndex = _startingIndex;
@synthesize endingIndex   = _endingIndex;

- (void)dealloc
{
    _arrayOfFrames = nil;
}

- (id)initWithTarget:(id)target action:(SEL)action
{
    self = [super initWithTarget:target action:action];
    if (self)
    {
        _arrayOfFrames = [[NSMutableArray alloc] init];
    }
    return self;
}

- (void)addSubviewToArrayOfFrames:(UIView *)view
{
    [_arrayOfFrames addObject:[NSValue valueWithCGRect:view.frame]];
}

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event 
{
    [super touchesBegan:touches withEvent:event];

    UITouch *touch = [touches anyObject];
    CGPoint location = [touch locationInView:self.view];

    for (NSInteger i = 0; i < [_arrayOfFrames count]; i++)
    {
        if (CGRectContainsPoint([[_arrayOfFrames objectAtIndex:i] CGRectValue], location)) 
        {
            self.startingIndex = i;
            return;
        }
    }

    self.startingIndex = -1;
    self.endingIndex = -1;
    self.state = UIGestureRecognizerStateCancelled;
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    [super touchesEnded:touches withEvent:event];

    UITouch *touch = [touches anyObject];
    CGPoint location = [touch locationInView:self.view];

    for (NSInteger i = 0; i < [_arrayOfFrames count]; i++)
    {
        if (CGRectContainsPoint([[_arrayOfFrames objectAtIndex:i] CGRectValue], location)) 
        {
            self.endingIndex = i;
            return;
        }
    }

    self.endingIndex = -1;
    self.state = UIGestureRecognizerStateCancelled;
}

@end

然后您可以按如下方式使用:

- (void)viewDidLoad
{
    [super viewDidLoad];

    PanBetweenSubviewsGestureRecognizer *pan = [[PanBetweenSubviewsGestureRecognizer alloc] initWithTarget:self action:@selector(pan:)];
    [pan addSubviewToArrayOfFrames:self.view0];
    [pan addSubviewToArrayOfFrames:self.view1];
    [pan addSubviewToArrayOfFrames:self.view2];

    [self.view addGestureRecognizer:pan];

    // Do any additional setup after loading the view.
}

- (void)pan:(PanBetweenSubviewsGestureRecognizer *)sender
{
    if (sender.state == UIGestureRecognizerStateEnded && sender.startingIndex >= 0 && sender.endingIndex >= 0 && sender.startingIndex != sender.endingIndex)
    {
        // successfully moved between subviews!
        NSLog(@"Moved from %1d to %1d", sender.startingIndex, sender.endingIndex);
    }
}

关于objective-c - 在一个 Action 中观察多个 View 上的触摸，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/11443213/