如何在iPhone上进行捏合手势？

发布于 2024-07-26 19:34:04 字数 94 浏览 11 评论 0原文

如何在 iPhone 上实现捏合手势？我熟悉在 iPhone 上使用触摸事件，但我非常懒，不想为像捏手势这样广泛使用的东西重新发明轮子......源代码或链接会很有帮助。

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苦笑流年记忆 2024-08-02 19:34:04

您需要使用一些基本数学知识自己实现它。

(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event;
(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event;

这些是您需要在应用程序中实现的委托方法。

您需要获取两次触摸之间的距离，然后在您自己的代码中计算距离的变化。

用于获取距离的数学方程称为点积

我只想指出他们在引用的教程中使用的方程是不正确的。
我已对其进行了更新，以包含教程中遗漏的绝对值。

这是点积：

- (CGFloat)distanceBetweenTwoPoints:(CGPoint)fromPoint toPoint:(CGPoint)toPoint
{
    float xDist = fromPoint.x - toPoint.x;
    float yDist = fromPoint.y - toPoint.y;

    float result = sqrt( pow(xDist,2) + pow(yDist,2) );
    return result;
}

编辑：
我在之前的答案中犯了一个错误……我已经有一段时间没有做过此类数学运算了。

如果不对结果求平方根，则无法获得点之间的真实距离。这称为计算两个向量之间的幅度。

这是正确的做法。如果你想省略 sqrt，你将无法得到两点之间的精确距离。

如果您不计算答案的平方，您的代码将有效，但它将使用比实际值大得多的测量值。因此，将来如果您需要获取两点之间的距离，它将返回类似 90000 的值，而不是实际的像素距离（300px）。

You need to implement it yourself using some basic math.

(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event;
(void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event;

Those are the delegate methods that you need to implement in your application.

You need to get the distance between the two touches, then calculate the changes in distance in your own code.

The mathematical equation you use to get the distance is called the dot product

I just want to point out that the equation they use in the cited tutorial is incorrect.
I have updated it to include the absolute value that is missed in the tutorial.

This is the dot product:

- (CGFloat)distanceBetweenTwoPoints:(CGPoint)fromPoint toPoint:(CGPoint)toPoint
{
    float xDist = fromPoint.x - toPoint.x;
    float yDist = fromPoint.y - toPoint.y;

    float result = sqrt( pow(xDist,2) + pow(yDist,2) );
    return result;
}

Edit:
I made a mistake in my previous answer....it's been a while since I've done any of that kind of math.

If you don't square root the result, you won't get the true distance between the points. This is called calculating the magnitude between two vectors.

This is the proper way to do it. If you want to omit the sqrt, you will not have the exact distance between the two points.

If you don't square the answer, your code will work but it will be using measurements that are much larger than the actual values. So in the future if you need to get the distance between the two points, it will return something like 90000 instead of the actual pixel distance which would be 300px.

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