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我有一个视图，在里面我添加了一个标签，然后我尝试使用 PanGesture 设置移动标签的边界。下面是我的代码：

@objc func handlePan(_ gestureRecognizer: UIPanGestureRecognizer) {
    if gestureRecognizer.state == .began || gestureRecognizer.state == .changed {
        let translation = gestureRecognizer.translation(in: self)
        if let view = gestureRecognizer.view {

            if (view.frame.origin.x + translation.x >= 0) && (view.frame.origin.y + translation.y >= 0) && (view.frame.origin.x + translation.x <= view.frame.width) && (view.frame.origin.y + translation.y <= view.frame.height)
            {
                view.center = CGPoint(x:view.center.x + translation.x,
                                       y:view.center.y + translation.y)
            }
        }
        gestureRecognizer.setTranslation(CGPoint.zero, in: self)
    }

}

我参考了这个答案：https ://stackoverflow.com/a/49008808/9970928

但它不起作用，谁能告诉我在这种情况下缺少什么？

4

1 回答 1

2

该代码不是最直观的，但假设其他一切正常，问题是它只超出了右侧和底部的界限。看看你的情况：

(view.frame.origin.x + translation.x <= view.frame.width)
(view.frame.origin.y + translation.y <= view.frame.height)

所以它说原点可能不会大于边界的大小你想要做的是检查内部视图的最大值：

(view.frame.maxX + translation.x <= view.frame.width)
(view.frame.maxY + translation.y <= view.frame.height)

但是这个过程通常会产生问题。想象一下，用户非常快速地向右滑动。并且最大值center.x可能是100。当前center.x是50并且用户将其在单个帧中拖动到200. 您的条件将失败，您的标签将保留在50而不是100. 我会把框架固定在边界上。

应该执行以下操作：

func clampFrame(_ frame: CGRect, inBounds bounds: CGRect) -> CGRect {
    let center: CGPoint = CGPoint(x: max(bounds.minX + frame.width*0.5, min(frame.midX, bounds.maxX - frame.width*0.5)),
                                  y: max(bounds.minY + frame.height*0.5, min(frame.midY, bounds.maxY - frame.height*0.5)))
    return CGRect(x: center.x-frame.width*0.5, y: center.y-frame.height*0.5, width: frame.width, height: frame.height)
}

func moveFrame(_ frame: CGRect, by translation: CGPoint, constrainedTo bounds: CGRect) -> CGRect {
    var newFrame = frame
    newFrame.origin.x += translation.x
    newFrame.origin.y += translation.y
    return clampFrame(newFrame, inBounds: bounds)
}

使用“翻译”程序可能还有其他问题。我会去寻找一个可以看到的位置。请参阅以下工作示例：

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let myView = MyView(frame: CGRect(x: 100.0, y: 100.0, width: 200.0, height: 200.0))
        myView.backgroundColor = UIColor.green
        view.addSubview(myView)
        let label = UILabel(frame: .zero)
        label.backgroundColor = UIColor.blue.withAlphaComponent(0.2)
        label.font = UIFont.systemFont(ofSize: 50.0)
        label.text = "Hi!"
        label.sizeToFit()
        myView.addSubview(label)
        label.addGestureRecognizer(UIPanGestureRecognizer(target: myView, action: #selector(MyView.handlePan)))
        label.isUserInteractionEnabled = true
    }


}

class MyView: UIView {

    func clampFrame(_ frame: CGRect, inBounds bounds: CGRect) -> CGRect {
        let center: CGPoint = CGPoint(x: max(bounds.minX + frame.width*0.5, min(frame.midX, bounds.maxX - frame.width*0.5)),
                                      y: max(bounds.minY + frame.height*0.5, min(frame.midY, bounds.maxY - frame.height*0.5)))
        return CGRect(x: center.x-frame.width*0.5, y: center.y-frame.height*0.5, width: frame.width, height: frame.height)
    }

    func moveFrame(_ frame: CGRect, by translation: CGPoint, constrainedTo bounds: CGRect) -> CGRect {
        var newFrame = frame
        newFrame.origin.x += translation.x
        newFrame.origin.y += translation.y
        return clampFrame(newFrame, inBounds: bounds)
    }

    private var startLocation: CGPoint = .zero
    private var startFrame: CGRect = .zero

    @objc func handlePan(_ gestureRecognizer: UIPanGestureRecognizer) {
        guard let label = gestureRecognizer.view else { return }

        if gestureRecognizer.state == .began {
            startLocation = gestureRecognizer.location(in: self)
            startFrame = label.frame
        } else if gestureRecognizer.state == .changed {
            let newLocation = gestureRecognizer.location(in: self)
            let translation = CGPoint(x: newLocation.x-startLocation.x, y: newLocation.y-startLocation.y)

            label.frame = moveFrame(startFrame, by: translation, constrainedTo: self.bounds)
        }

    }

}
于 2019-04-03T07:02:26.690 回答