iOS: "recognizer.view.center = CGPointMake(..."的错误效果

Question

我正在使用 locationInView 来设置用户释放按钮时的位置。释放后，我给出了之前存储的位置，但实际上，我的按钮并没有回到正确的位置。

这是我的代码:

- (IBAction)handlePan:(UIPanGestureRecognizer *)recognizer{

    CGPoint translation = [recognizer translationInView:self.view];
    recognizer.view.center = CGPointMake(recognizer.view.center.x + translation.x,
                                         recognizer.view.center.y + translation.y);

    [recognizer setTranslation:CGPointMake(0, 0) inView:self.view];

    static CGPoint startLocation;

    if (recognizer.state == UIGestureRecognizerStateBegan) {
        startLocation = [recognizer locationInView:self.view];
        NSLog(@"Began: %d" @"-" @"%d", (int)startLocation.x , (int)startLocation.y);
    }

    if (recognizer.state == UIGestureRecognizerStateEnded)
    {
        NSLog(@"Ended Bef: %d" @"-" @"%d", (int)startLocation.x, (int)startLocation.y);
        recognizer.view.center =  CGPointMake(startLocation.x, startLocation.y);

        startLocation = [recognizer locationInView:self.view];
        NSLog(@"Ended Aft: %d" @"-" @"%d", (int)startLocation.x, (int)startLocation.y);

    }

 }

其实指令:

recognizer.view.center =  CGPointMake(startLocation.x, startLocation.y);

产生错误的效果。有人知道为什么吗？

Answer 1

几个想法:

1. 我建议您在更改 center 之前确保捕获 startLocation。

2. 您正在使用用户触摸的位置作为 startLocation。您确实应该使用 recognizer.view 的 center 对其进行初始化。用户不太可能在按钮的中心准确地开始他们的手势。因此，您不太可能回到原来的位置。

有点不相关，但是:

1. 在UIGestureRecognizerStateEnded<中重置recognizer.view的center时不需要使用CGMakePoint/ 子句。如果确实需要，可以使用 CGPointMake，但没有必要。如果需要，您可以只使用 startLocation。

2. 您可能想要动画化 View 返回到 startLocation。让它立即去那里是不和谐的。

3. 顺便说一句，如果您保存了 startLocation，则不需要不断地重置 translation。只需使用 startLocation 加上 translation。对我来说似乎更清楚，但显然这是主观的。

4. 我个人认为 NSStringFromCGPoint 在记录 CGPoint 结构时非常有用。

所以，我建议:

- (IBAction)handlePan:(UIPanGestureRecognizer *)recognizer
{
    static CGPoint startLocation;

    if (recognizer.state == UIGestureRecognizerStateBegan)
    {
        startLocation = recognizer.view.center;
        NSLog(@"Began: %@", NSStringFromCGPoint(startLocation));
    }

    CGPoint translation = [recognizer translationInView:self.view];

    recognizer.view.center = CGPointMake(startLocation.x + translation.x,
                                         startLocation.y + translation.y);

    if (recognizer.state == UIGestureRecognizerStateEnded)
    {
        NSLog(@"Ended Bef: %@", NSStringFromCGPoint(startLocation));

        [UIView animateWithDuration:0.25
                         animations:^{
                             recognizer.view.center = startLocation;
                         }];

        CGPoint finalLocation = [recognizer locationInView:self.view];
        NSLog(@"Ended Aft: %@", NSStringFromCGPoint(finalLocation));
    }
}