iOS:“recognizer.view.center = CGPointMake(..."; [英] iOS: Wrong effect with "recognizer.view.center = CGPointMake(..."

问题描述

我正在使用 locationInView 来设置当用户释放它时我的 boton 的位置.释放后，我给出了之前存储的位置，但实际上，我的按钮没有回到正确的位置.

I am using the locationInView to set the position of my bouton when the user release it. After release, I give the location stored before but in fact, my button is not going back to the correct position.

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);

    }

 }

其实就是指令:

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

产生错误的效果.有人知道为什么吗?

give a wrong effect. Someone know why?

推荐答案

一些想法:

1. 我建议您在对 center 进行任何更改之前确保捕获 startLocation.

1. I'd suggest making sure you capture startLocation before you do any changing of the center.

您将用户触摸的位置用于 startLocation.你真的应该用 recognizer.view 的 center 来初始化它.用户极不可能在按钮的中心开始他们的手势.因此，您不太可能回到原来的位置.

You're using the location of the user's touch for startLocation. You really should initialize this with the center of the recognizer.view. It's exceedingly unlikely that the user started their gesture precisely in the center of the button. And as a result, you're unlikely to return back at the original location.

有点不相关，但是:

1. 在UIGestureRecognizerStateEndedrecognizer.view的center重置时，不需要使用CGMakePoint/code> 子句.如果您真的需要，您可以使用 CGPointMake，但这是不必要的.如果需要，您可以只使用 startLocation.

1. You don't need to use CGMakePoint when resetting the center of recognizer.view in the UIGestureRecognizerStateEnded clause. You can use CGPointMake if you really want, but it's unnecessary. You can just use startLocation, if you want.

您可能想要动画返回到那个 startLocation 的视图.让它立即去那里很刺耳.

You might want to animate the returning of the view back to that startLocation. It's jarring to have it immediately go there.

顺便说一句，如果您已保存startLocation，则无需不断重置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.

As an aside, if you've saved startLocation, you don't need to continually reset the translation. Just use startLocation plus translation. Seems more clear to me, but clearly that's subjective.

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

I personally think NSStringFromCGPoint is very useful when logging CGPoint structures.

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));
    }
}

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