ios - 在 UIScrollView 中绘制 UIImageView

Question

我在 UIScrollView 中有一个 UIImageView，它会自动缩小以适应提供的图像。用户可以像往常一样使用捏合手势进行缩放，并且平移手势设置为需要两次触摸，因为绘图优先。

启动时，一切看起来都很棒，但是当我调用我的绘图代码时，会发生这种情况:

如您所见，调用 drawLineFrom(fromPoint:toPoint:) 时，UIImageView 会缩小。之后，绘图似乎按预期工作(尽管它在每次触摸时都会跳过该行的第一部分)。

我的 UIPanGestureRecognizer 选择器:

@objc func onOneFingerDrawing(_ sender: UIPanGestureRecognizer) {
    switch sender.state {
    case .began:
        swiped = false

        lastPoint = sender.location(in: drawView.imageView)
    case .changed:
        swiped = true

        let currentPoint = sender.location(in: drawView.imageView)
        drawLineFrom(fromPoint: lastPoint, toPoint: currentPoint)

        lastPoint = currentPoint
    case .ended:
        guard drawView.scrollView.frame.contains(sender.location(in: drawView.imageView)) else {
            return
        }

        if let newImage = drawView.imageView.image {
            if history.count > historyIndex + 1 {
                history.removeLast((history.count - 1) - historyIndex)
            }

            history.append(newImage)
            historyIndex = history.count - 1
        }
    case .possible,
         .cancelled,
         .failed:
        return
    }
}

和我的drawLineFrom(fromPoint:toPoint:):

@objc func drawLineFrom(fromPoint: CGPoint, toPoint: CGPoint) {
    UIGraphicsBeginImageContextWithOptions(drawView.imageView.frame.size, false, UIScreen.main.scale)
    let context = UIGraphicsGetCurrentContext()
    context?.interpolationQuality = .none

    drawView.imageView.image?.draw(in: CGRect(x: 0, y: 0, width: drawView.imageView.frame.size.width, height: drawView.imageView.frame.size.height))

    context?.move(to: fromPoint)
    context?.addLine(to: toPoint)

    context?.setLineCap(.round)
    context?.setLineWidth(lineWidth)
    context?.setStrokeColor(lineColor)
    context?.setBlendMode(blendMode)

    context?.strokePath()

    let newImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    drawView.imageView.image = newImage
}

Answer 1

ScrollView 的图像约束存在问题。每当您开始渲染图像时，它的框架就会根据内容发生变化。因此，您需要向 ImageView 添加宽高比约束(就像我所做的那样)或任何大小约束。查看 gif 以供引用。

Before add image view size constraint.

After adding image view size constraint.