UIImage.DrawInRect causes error/notification

Question

Create a simple app, and can't do it without an error

I don't really know why bg.drawInRect doesn't cause an error when player.drawInRect causing? And the problem is that image doesn't drawing/redrawing when we change coordinates

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

You need to start your timer outside your drawRect call; didMoveToSuperview might be a good place, but it depends on what you're trying to accomplish. Then, in timerRedraw, call setNeedsDisplay() to trigger a re-draw.

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()
}

I highly recommend reading Apple's Drawing and Printing Guide for iOS, it explains everything you need to know to get started with doing custom drawing in iOS.