ios - UIImage.DrawInRect 导致错误/通知

Question

创建一个简单的应用程序，并且不能不出错

我真的不知道为什么当 player.drawInRect 导致错误时 bg.drawInRect 不会导致错误？问题是当我们改变坐标时图像不会绘制/重绘

Sep 16 22:13:16 imac-admin.lan Letalka_drawrect[804] : 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.

Answer 1

您需要在 drawRect 调用之外启动计时器； didMoveToSuperview可能是个好地方，但这取决于您要完成的目标。然后，在 timerRedraw 中，调用 setNeedsDisplay()触发重新绘制。

var timer: NSTimer?

override func didMoveToSuperview() {
    // Stop the timer if it was already running
    if timer != nil {
        timer.invalidate()
        timer = nil
    }

    // Only start the timer if the view is actually part of a view hierarchy
    if superview != nil {
        timer = NSTimer.scheduledTimerWithTimeInterval(interval, target: self, selector: "timerRedraw", userInfo: nil, repeats: true)
    }
}

func timerRedraw() {
    x += 5
    y += 6
    setNeedsDisplay()
}

我强烈推荐阅读 Apple 的 Drawing and Printing Guide for iOS ，它解释了开始在 iOS 中进行自定义绘图所需了解的一切。