objective-c - 如何检测屏幕上没有手指？

Question

我需要touchesEnded函数的帮助。我想使用NSTimer函数在屏幕上没有手指时启动touchesEnded。这可能吗？。目前，我有一个touchesBegan函数正在工作:-)。

这是我的代码:

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    NSUInteger numTaps = [[touches anyObject] tapCount];

    if (numTaps >= 2)
    {
        self.label.text = [NSString stringWithFormat:@"%d", numTaps];
        self.label2.text = @"+1";
        [self.button setHidden:YES];
    }
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
}

- (void)showButton
{
    [self.button setHidden:NO];
}

Answer 1

这很棘手。您不会得到一个告诉您所有手指都向上的事件。每个touchesEnded仅告诉您该手指向上。因此，您必须自己跟踪触摸。通常的技术是在触摸到达时将其存储在可变集中。但是您不能自己存储触摸，因此必须存储一个标识符。

首先在UITouch上放置一个类别，以派生此唯一标识符:

@interface UITouch (additions)
- (NSString*) uid;
@end

@implementation UITouch (additions)
- (NSString*) uid {
    return [NSString stringWithFormat: @"%p", self];
}
@end

现在，我们必须在有触摸的整个过程中保持可变的设置，在第一次触摸时创建它，并在最后一次触摸消失时销毁它。我假设您有一个NSMutableSet实例变量/属性。这是伪代码:

- (void) touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
    // create mutable set if it doesn't exist
    // then add each touch's uid to the set with addObject:
    // and then go on and do whatever else you want to do
}

- (void) touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
    // remove uid of *every* touch that has ended from our mutable set
    // if *all* touches are gone, nilify the set
    // now you know that all fingers are up
}