在UISplitViewController中绘制的奇怪错误

Question

我试图制作带有用户可以绘制内容的视图的屏幕。我用这样的代码创建了自定义视图：

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    swiped = false
    if let touch = touches.first {
        lastPoint = touch.location(in: imageView)
    }
}

override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
    swiped = true
    if let touch = touches.first {
        let currentPoint = touch.location(in: imageView)
        drawLine(fromPoint: lastPoint, toPoint: currentPoint)

        lastPoint = currentPoint
    }
}

override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
    if !swiped {
        // draw a single point
        drawLine(fromPoint: lastPoint, toPoint: lastPoint)
    }

和绘图功能

func drawLine(fromPoint: CGPoint, toPoint: CGPoint) {
    UIGraphicsBeginImageContext(imageView.frame.size)
    let context = UIGraphicsGetCurrentContext()
    imageView.image?.draw(in: CGRect(x: 0, y: 0, width: imageView.frame.size.width, height: imageView.frame.size.height))

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

    context?.setLineCap(.round)
    context?.setLineWidth(lineWidth)
    context?.setStrokeColor(lineColor.cgColor)

    context?.strokePath()

    imageView.image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
}

当我在视图控制器中显示该视图时，一切正常：

但是当我在UISplitViewController中的详细视图中显示它时，当用户继续绘图时，部分已经绘制了图像移动和淡出：

我无法找到关于网络中的哪些错误的内容，也不知道是什么产生了这样的行为

有人对此有任何想法吗？

这是您可以重现该错误的示例项目： https://github.com/fizzy871/DrawingBug

不过，在实际项目中，不仅分割视图控制器的主视图，而且导航栏也影响绘图

Answer 1

原来它的行为是这样的，因为imageView框架的大小是小数部分。

我只是将绘图上下文乘以2并解决了问题：

func drawLine(fromPoint fromPoint: CGPoint, toPoint: CGPoint) {
    // multiply to avoid problems when imageView frame value is XX.5
    let fixedFrameForDrawing = CGRect(x: 0, y: 0, width: imageView.frame.size.width*2, height: imageView.frame.size.height*2)
    let point1 = CGPoint(x: fromPoint.x*2, y: fromPoint.y*2)
    let point2 = CGPoint(x: toPoint.x*2, y: toPoint.y*2)
    UIGraphicsBeginImageContext(fixedFrameForDrawing.size)
    if let context = UIGraphicsGetCurrentContext() {
        imageView.image?.draw(in: fixedFrameForDrawing)

        context.move(to: point1)
        context.addLine(to: point2)

        context.setLineCap(.round)
        context.setLineWidth(lineWidth*2)
        context.setStrokeColor(lineColor.cgColor)

        context.strokePath()

        let imageFromContext = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        imageView.image = imageFromContext
    }