使用UIPanGestureRecognizer在有限区域内拖动UIView [英] Use UIPanGestureRecognizer to drag UIView inside limited area

问题描述

我想允许用户将UIView拖动到其超级视图的有限区域内。尝试以下简单代码：

I want to allow user to drag UIView inside a limited area of its super view. Trying the following simple code:

func handlePanForImage(recognizer: UIPanGestureRecognizer) {

    if let myView = recognizer.view {

        switch (recognizer.state) {

        case .Changed:

            let translation = recognizer.translationInView(self)

            if insideDraggableArea(myView.center) {                
                myView.center =  CGPoint(x:recognizer.view!.center.x + translation.x, y:recognizer.view!.center.y + translation.y)
                recognizer.setTranslation(CGPointZero, inView: self)
            }

        default:
            break
        }
    }
}

我看到确实没有将视图拖到有限区域之外，但是当我尝试再次将其从他的最后一个有效位置拖动。

I see that indeed the view is not dragged outside the limited area, however when I try to drag it again from his last valid position nothing happens.

我在这里错过了什么？

推荐答案

解释在其他一些帖子中，我首先需要计算新位置，然后检查新位置是否在范围内，并且只有在更新视图的坐标时才可以：

As explain in some other posts, I needed first to compute the new location, then check if the new location is inside the bounds, and only if it is update the view's coordinates:

        let translation = recognizer.translationInView(self)
        let newPos = CGPoint(x:recognizer.view!.center.x + translation.x, y:recognizer.view!.center.y + translation.y)

        if insideDraggableArea(newPos) {                
            myView.center =  newPos
            recognizer.setTranslation(CGPointZero, inView: self)
        }

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