ios - 省略 UIColor.setFill() 错误消息？

Question

我有两个并排的函数，它们循环不断地绘制两个 UIBezierPaths，问题是，它们每个都有不同的颜色，所以我经常需要重申 UIColor.blackColor().setFill() 和 UIColor(patternImage: UIImage(named: "normalpaper.jpg")).setFill()，缺点是它使控制台无法读取，因为它会无休止地向您发送警告消息。

<Error>: CGContextRestoreGState: invalid context 0x0. This is a serious error.
This application, or a library it uses, is using an invalid context  and is thereby
contributing to an overall degradation of system stability and reliability. This
notice is a courtesy: please fix this problem. It will become a fatal error in an
upcoming update.

因此，这是我的问题，有没有一种方法可以做到这一点，而不会将此警告消息发送到我的控制台？也许是一种使警告消息不会出现的方法？ (无法通过搜索找到一个)或者可能是一种省略消息的方式？非常感谢任何输入，感谢阅读 -Zach。

-

如果你需要绘图函数，它们在下面

func drawCircle() {

    //Setting the draw color
    UIColor.blackColor().setFill()

    // Creating the rectangle's size
    var drawRect = roundDrawRect(10.0, angle: 7)

    //Incrementing the coords
    ++y
    ++x

    //Drawing the rectangle
    drawRect.fill()

}

func eraseCircle() {

    //Setting the eraser color
    UIColor(patternImage: UIImage(named: "normalpaper.jpg")).setFill()

    //Decrementing the coords
    eraseX = x - 2
    eraseY = y - 2

    // Creating the rectangle's size
    var eraseRect = roundEraseRect(10.0, angle: 7)

    //Drawing the rectangle
    eraseRect.fill()

}

下面是完整的 CircleView 类(我对编程还是很陌生，所以它可能效率很低)

//Creating a view capable of painting the circle
class CircleView: UIView {

//Starting X Pos
var x: CGFloat = 100
var eraseX: CGFloat = 100

//Starting Y Pos
var y: CGFloat = 100
var eraseY: CGFloat = 100

//Starting the loop of functions
override func drawRect(rect: CGRect) {

    //Creating the looping draw timer
    NSTimer.scheduledTimerWithTimeInterval(
        0.2,
        target: self,
        selector: Selector("timerDraw"),
        userInfo: nil,
        repeats: true)

    //Creating the looping erase timer
    NSTimer.scheduledTimerWithTimeInterval(
        0.3,
        target: self,
        selector: Selector("timerErase"),
        userInfo: nil,
        repeats: true)

}

func drawCircle() {

    //Setting the draw color
    UIColor.blackColor().setFill()

    // Creating the rectangle's size
    var drawRect = roundDrawRect(10.0, angle: 7)

    //Incrementing the coords
    ++y
    ++x

    //Drawing the rectangle
    drawRect.fill()

}

func eraseCircle() {

    //Setting the eraser color
    UIColor(patternImage: UIImage(named: "normalpaper.jpg")).setFill()

    //Decrementing the coords
    eraseX = x - 2
    eraseY = y - 2

    // Creating the rectangle's size
    var eraseRect = roundEraseRect(10.0, angle: 7)

    //Drawing the rectangle
    eraseRect.fill()

}

func timerDraw(){

    //DO DRAW LOOP HERE
    drawCircle()

}

func timerErase(){

    //DO ERASE LOOP HERE
    eraseCircle()

}

//Defining the rounded rect erasing (Circle)
func roundEraseRect(radius: CGFloat, angle: CGFloat) -> UIBezierPath {

    //Creating the rounded rect (Circle)
    var roundedRect = UIBezierPath()

    roundedRect.moveToPoint(CGPointMake(eraseX,eraseY))
    println(CGPointMake(eraseX,eraseY))

    roundedRect.addArcWithCenter(CGPointZero, radius: radius,
        startAngle: 0, endAngle: angle ,
        clockwise: true)

    return roundedRect
}

//Defining the rounded rect drawing (Circle)
func roundDrawRect(radius: CGFloat, angle: CGFloat) -> UIBezierPath {

    //Creating the rounded rect (Circle)
    var roundedRect = UIBezierPath()

    roundedRect.moveToPoint(CGPointMake(x,y))

    roundedRect.addArcWithCenter(CGPointZero, radius: radius,
        startAngle: 0, endAngle: angle ,
        clockwise: true)

    return roundedRect
}




}

class ViewController: UIViewController {

Answer 1

Apple 的 Drawing and Printing Guide for iOS解释了所有这些，我强烈建议在进一步使用自定义绘图代码之前阅读它。至少，请阅读有关 iOS Drawing Concepts 的部分.

---

问题是您在 CircleView 的 drawRect 函数中创建并触发了 NSTimer。绘图调用只能在正确的上下文中进行(这实际上是您看到它试图告诉您的错误)。通过在从 NSTimer 调用的函数中进行绘图，您实际上是在 您的 drawRect 函数中进行绘图，并且没有有效的在这种情况下绘制上下文。另外，按照现在的代码，每次系统需要重绘 View 时，您都会启动新的计时器；随着计时器开始重叠，这可能很快就会失控。

但是，只需稍微重新安排一下，我们就可以完成这项工作。

请注意:这不一定是处理圆形动画的正确方法，但它会解决您提出的特定问题关于无效上下文错误。

1. 从 drawRect 中取出所有内容，并将其替换为对 eraseCircle 和 drawCircle 的调用。

2. 采用必须递增 x 和 y 以及 eraseX 和 eraseY 的逻辑从 drawCircle 和 eraseCircle 中取出，并将其放入 timerDraw 和 timerErase 中。

3. 不要直接在timerDraw 和timerErase 中调用绘图代码，而是通过调用setNeedsDisplay() 告诉 View 系统您需要重绘 View 。 .这会将您的 View 标记为需要重绘，并且 View 系统会尽快自动再次调用您的 drawRect 函数。

4. 通过覆盖 didMoveToSuperview 并在那里启动它们，让您的计时器再次工作；如果它们已经在运行，您还应该添加停止它们的逻辑。

第 1 步和第 3 步是消除错误的关键部分。

像这样:

//Creating a view capable of painting the circle
class CircleView: UIView {
    // Timers
    var drawTimer: NSTimer?
    var eraseTimer: NSTimer?

    //Starting X Pos
    var x: CGFloat = 100
    var eraseX: CGFloat = 100

    //Starting Y Pos
    var y: CGFloat = 100
    var eraseY: CGFloat = 100

    override func drawRect(rect: CGRect) {
        eraseCircle()
        drawCircle()
    }

    override func didMoveToSuperview() {
        // If we have active timers, stop them
        if var drawTimer = self.drawTimer {
            // This stops the timer
            drawTimer.invalidate()
            self.drawTimer = nil
        }

        if var eraseTimer = self.eraseTimer {
            // This stops the timer
            eraseTimer.invalidate()
            self.eraseTimer = nil
        }

        // If we're actually part of the view hierarchy, start the timers
        if self.superview != nil {
            //Creating the looping draw timer
            self.drawTimer = NSTimer.scheduledTimerWithTimeInterval(
                0.2,
                target: self,
                selector: Selector("timerDraw"),
                userInfo: nil,
                repeats: true)

            //Creating the looping erase timer
            self.eraseTimer = NSTimer.scheduledTimerWithTimeInterval(
                0.3,
                target: self,
                selector: Selector("timerErase"),
                userInfo: nil,
                repeats: true)
        }
    }

    func drawCircle() {
        //Setting the draw color
        UIColor.blackColor().setFill()

        // Creating the rectangle's size
        var drawRect = roundDrawRect(10.0, angle: 7)

        //Drawing the rectangle
        drawRect.fill()

    }

    func eraseCircle() {
        //Setting the eraser color
        UIColor(patternImage: UIImage(named: "normalpaper.jpg")).setFill()

        // Creating the rectangle's size
        var eraseRect = roundEraseRect(10.0, angle: 7)

        //Drawing the rectangle
        eraseRect.fill()

    }

    func timerDraw(){
        //Incrementing the coords
        ++y
        ++x

        self.setNeedsDisplay()
    }

    func timerErase(){
        //Decrementing the coords
        eraseX = x - 2
        eraseY = y - 2

        self.setNeedsDisplay()
    }

    //Defining the rounded rect erasing (Circle)
    func roundEraseRect(radius: CGFloat, angle: CGFloat) -> UIBezierPath {

        //Creating the rounded rect (Circle)
        var roundedRect = UIBezierPath()

        roundedRect.moveToPoint(CGPointMake(eraseX,eraseY))
        println(CGPointMake(eraseX,eraseY))

        roundedRect.addArcWithCenter(CGPointZero, radius: radius,
            startAngle: 0, endAngle: angle ,
            clockwise: true)

        return roundedRect
    }

    //Defining the rounded rect drawing (Circle)
    func roundDrawRect(radius: CGFloat, angle: CGFloat) -> UIBezierPath {

        //Creating the rounded rect (Circle)
        var roundedRect = UIBezierPath()

        roundedRect.moveToPoint(CGPointMake(x,y))

        roundedRect.addArcWithCenter(CGPointZero, radius: radius,
            startAngle: 0, endAngle: angle ,
            clockwise: true)

        return roundedRect
    }
}

至于实现您正在尝试的动画的最佳方式，您可以考虑只绘制一次圆圈，然后在您的 UIViewController 中在计时器上移动整个 View 。或者，可能更好，使用 Core Animation .或者，如果您的最终产品将是一款游戏(甚至是类似游戏)，也许可以看看 Sprite Kit .