让用户绘制矩形来选择一个区域

Posted 2023-02-25

【中文标题】让用户绘制矩形来选择一个区域

【英文标题】：let user to draw rectangle to select an area

【发布时间】：2016-02-05 20:31:30

【问题描述】：

我是 Swift 的新手，我试图让用户绘制一个矩形（触摸和拖动）来选择图像的一个区域，就像裁剪时一样，但我不想裁剪我只想知道用户创建的 CGRect。

到目前为止，我有一个 .xib，里面有一个 UIImage 和它的 ViewController。我想在图像上方绘制，但我发现的每个关于绘图的教程都是关于子类化 UIView、覆盖 drawRect 并将其作为 xib 类。

【问题讨论】：

继承 UIView 并覆盖 drawRect 有什么问题？

【参考方案1】：

我想通了。我刚刚创建了一个 uiview 并根据触摸事件更改其框架

let overlay = UIView()
var lastPoint = CGPointZero

override func viewDidLoad() 
    super.viewDidLoad()

    // Do any additional setup after loading the view.
    overlay.layer.borderColor = UIColor.blackColor().CGColor
    overlay.backgroundColor = UIColor.clearColor().colorWithAlphaComponent(0.5)
    overlay.hidden = true
    self.view.addSubview(overlay)



override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) 

    //Save original tap Point
    if let touch = touches.first 
        lastPoint = touch.locationInView(self.view)
       


override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent?) 
    //Get the current known point and redraw
    if let touch = touches.first 
        let currentPoint = touch.locationInView(view)
        reDrawSelectionArea(lastPoint, toPoint: currentPoint)
    


func reDrawSelectionArea(fromPoint: CGPoint, toPoint: CGPoint) 
    overlay.hidden = false

        //Calculate rect from the original point and last known point
        let rect = CGRectMake(min(fromPoint.x, toPoint.x),
        min(fromPoint.y, toPoint.y),
        fabs(fromPoint.x - toPoint.x),
        fabs(fromPoint.y - toPoint.y));

    overlay.frame = rect


override func touchesEnded(touches: Set<UITouch>, withEvent event: UIEvent?) 
    overlay.hidden = true

    //User has lift his finger, use the rect
    applyFilterToSelectedArea(overlay.frame)

    overlay.frame = CGRectZero //reset overlay for next tap

【讨论】：

什么是applyFilterToSelectedArea？你能把它的代码贴出来吗？