Question

我想让用户在A上绘制一个矩形我为最后一个触摸位置添加了两个变量我添加了这个功能： -

UIImageView

我将方法添加到（func draw(from: CGPoint, to: CGPoint) { UIGraphicsBeginImageContext(imageView.frame.size) context = UIGraphicsGetCurrentContext() context?.setStrokeColor(UIColor(red: 0, green: 0, blue: 0, alpha: 1.0).cgColor) context?.setLineWidth(5.0) let currentRect = CGRect(x: from.x, y: from.y, width: to.x - from.x, height: to.y - from.y) context?.addRect(currentRect) context?.drawPath(using: .stroke) context?.strokePath() imageView.image?.draw(in: self.imageView.frame) imageView.image = UIGraphicsGetImageFromCurrentImageContext() UIGraphicsEndImageContext() }）它绘制了许多矩形

我将方法添加到（touchMoved）它绘制一个，但是当用户移动触摸时它不会出现

touchEnded

我希望让用户在override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) { if let touch = touches.first { firstTouchLocation = touch.location(in: self.view) } } override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) { if let touch = touches.first { lastTouchLocation = touch.location(in: self.view) draw(from: firstTouchLocation, to: lastTouchLocation) } } override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) { if let touch = touches.first { lastTouchLocation = touch.location(in: self.view) draw(from: firstTouchLocation, to: lastTouchLocation) } }时扩展矩形，并在touchMoved时绘制。

Answer 1

您正在使用由前一个image组成的新图片以及在其上绘制的矩形替换您的image。不是从图像视图中绘制图像，而是绘制原始图像。

或者，您可以将矩形渲染为形状图层，然后只更新该形状图层的路径：

class ViewController: UIViewController {

    @IBOutlet weak var imageView: UIImageView!

    private let shapeLayer: CAShapeLayer = {
        let _shapeLayer = CAShapeLayer()
        _shapeLayer.fillColor = #colorLiteral(red: 0, green: 0, blue: 0, alpha: 0).cgColor
        _shapeLayer.strokeColor = #colorLiteral(red: 0, green: 0, blue: 0, alpha: 1).cgColor
        _shapeLayer.lineWidth = 3
        return _shapeLayer
    }()

    private var startPoint: CGPoint!

    override func viewDidLoad() {
        super.viewDidLoad()

        imageView.layer.addSublayer(shapeLayer)
    }

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        startPoint = touches.first?.location(in: imageView)
    }

    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        guard let startPoint = startPoint, let touch = touches.first else { return }

        let point: CGPoint

        if let predictedTouch = event?.predictedTouches(for: touch)?.last {
            point = predictedTouch.location(in: imageView)
        } else {
            point = touch.location(in: imageView)
        }

        updatePath(from: startPoint, to: point)
    }

    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        guard let startPoint = startPoint, let touch = touches.first else { return }

        let point = touch.location(in: imageView)

        updatePath(from: startPoint, to: point)
        imageView.image = imageView.snapshot(afterScreenUpdates: true)
        shapeLayer.path = nil
    }

    override func touchesCancelled(_ touches: Set<UITouch>, with event: UIEvent?) {
        shapeLayer.path = nil
    }

    private func updatePath(from startPoint: CGPoint, to point: CGPoint) {
        let size = CGSize(width: point.x - startPoint.x, height: point.y - startPoint.y)
        let rect = CGRect(origin: startPoint, size: size)
        shapeLayer.path = UIBezierPath(rect: rect).cgPath
    }

}

其中：

extension UIView {
    func snapshot(afterScreenUpdates: Bool = false) -> UIImage {
        UIGraphicsBeginImageContextWithOptions(bounds.size, isOpaque, 0)
        drawHierarchy(in: bounds, afterScreenUpdates: afterScreenUpdates)
        let image = UIGraphicsGetImageFromCurrentImageContext()!
        UIGraphicsEndImageContext()
        return image
    }
}

这不仅更简单，而且效率更高。

产量：

顺便说一下，我可能建议在touchesMoved中使用预测性触摸。在设备（不是模拟器）上，可以产生稍微响应的UI。

使用Core Graphics在UIImageView上绘制一个矩形

1 个答案: