Question

我跟随raywenderlich tutorial使用UIKit制作了一个绘图应用。我现在正在尝试添加撤消最后一笔中断的功能。理想情况下，我想撤消最多10个笔画。我想弄清楚这样做的最佳方法是什么。我正在考虑创建另一个ImageView，它只有最后一个笔划，并在用户按下时生成ImageView.image = nil。在教程的代码中有类似的东西。当触摸结束时，最新的笔划将合并到imageview上，所有旧笔划都在右侧不透明度。我不确定如何将这第三个（可能更多）imageivews添加到此代码中以使其工作。任何想法/更好的方式来解决这个问题？ touchesEnded的代码如下。

代码

override func touchesEnded(touches: Set<NSObject>, withEvent event: UIEvent) {

        if !swiped {
            // draw a single point
            drawLineFrom(lastPoint, toPoint: lastPoint)
        }

        // Merge tempImageView into mainImageView
        UIGraphicsBeginImageContext(mainImageView.frame.size)
        mainImageView.image?.drawInRect(CGRect(x: 0, y: 0, width: view.frame.size.width, height: view.frame.size.height), blendMode: kCGBlendModeNormal, alpha: 1.0)
        tempImageView.image?.drawInRect(CGRect(x: 0, y: 0, width: view.frame.size.width, height: view.frame.size.height), blendMode: kCGBlendModeNormal, alpha: opacity)
        mainImageView.image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        tempImageView.image = nil
    }

Answer 1

@SpaceShroomies：我找到了/想出了一个很好的解决方案..

我使用了nsHiptser和Raywenderlich tutorial中的部分。

这是我的解决方案：

override func touchesEnded(touches: Set<NSObject>, withEvent event: UIEvent) {
    //undoManager
    let undo: UIImageView = undoManager?.prepareWithInvocationTarget(Temp2Image) as! UIImageView

    UIGraphicsBeginImageContext(Temp2Image.frame.size)
    Temp2Image.image?.drawInRect(CGRect(x: 0, y: 0, width: Temp2Image.frame.size.width, height: Temp2Image.frame.size.height), blendMode: kCGBlendModeNormal, alpha: 1.0)
    TempImage.image?.drawInRect(CGRect(x: 0, y: 0, width: TempImage.frame.size.width, height: TempImage.frame.size.height), blendMode: kCGBlendModeNormal, alpha: opacity)
    undo.image = Temp2Image.image
    Temp2Image.image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    TempImage.image = nil
}

重要的是设置， UNDO 应该回到I.e. undo.image = Temp2Image.image否则它不会改变＆＃34;它＆＃34;回来

Answer 2

所以我设法让一个撤销功能向后退一步，通过一个UIImageView存储最后一个笔划，然后在下一个笔划完成时添加到其余笔划...使用时会出现问题倒退10步的技术相同？我需要10个UIImageViews ...这会效率低吗/导致崩溃吗？代码如下：

override func touchesEnded(touches: Set<NSObject>, withEvent event: UIEvent) {

        if !swiped {
            // draw a single point
            drawLineFrom(lastPoint, toPoint: lastPoint)
        }


        UIGraphicsBeginImageContext(mainImageView.frame.size)
        mainImageView.image?.drawInRect(CGRect(x: 0, y: 0, width: view.frame.size.width, height: view.frame.size.height), blendMode: kCGBlendModeNormal, alpha: 1.0)
        undo1.image?.drawInRect(CGRect(x: 0, y: 0, width: view.frame.size.width, height: view.frame.size.height), blendMode: kCGBlendModeNormal, alpha: 1.0)
        mainImageView.image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        undo1.image = nil

        UIGraphicsBeginImageContext(undo1.frame.size)
        undo1.image?.drawInRect(CGRect(x: 0, y: 0, width: view.frame.size.width, height: view.frame.size.height), blendMode: kCGBlendModeNormal, alpha: 1.0)
        tempImageView.image?.drawInRect(CGRect(x: 0, y: 0, width: view.frame.size.width, height: view.frame.size.height), blendMode: kCGBlendModeNormal, alpha: opacity)
        undo1.image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        tempImageView.image = nil
    }

添加撤消功能到绘图应用程序

2 个答案: