Omitting the UIColor.setFill() error message? - ios

Question

I have two functions side by side that are looped to constantly draw two UIBezierPaths, the thing is, each of them have a different color so I constantly need to reiterate UIColor.blackColor().setFill() and UIColor(patternImage: UIImage(named: "normalpaper.jpg")).setFill(), the downside is it makes the console impossible to read because it's endlessly spamming the warning message you get.
<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.
And thus, here is my question, is there a way of doing this that would not spam my console with this warning message? Perhaps a way of making it so the warning message would not appear? (Couldn't find one with searching) Or maybe a way of omitting the message? Any input is very appreciated, thanks for reading -Zach.
-
If you need the draw functions, there they are below
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()
}
Full CircleView class below
(I'm still very new to programming, so it's probably quite inefficient)
//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's Drawing and Printing Guide for iOS explains all of this, I highly recommend reading it before going further with custom drawing code. At an absolute minimum, read the section on iOS Drawing Concepts.
The problem is that you're creating and firing NSTimers inside your CircleViews drawRect function. Drawing calls can only be made in the right context (which is actually what the error you're seeing it trying to tell you). By doing the drawing in functions invoked from your NSTimer, you're actually doing the drawing outside your drawRect function and there isn't a valid drawing context in that case. Also, with the code the way it is, you'll be starting new timers each time the system needs to redraw your view; that could get out of hand very quickly as the timers start overlapping.
However, with just a bit of rearranging, we can make this work.
Please Note: This isn't necessarily the right way to go about what you're doing with your circle animation, but it will solve the particular problem that you're asking about with with regards to the invalid context error.
Take everything out of drawRect and replace it with calls to eraseCircle and drawCircle.
Take the logic that you have to increment x and y, and eraseX and eraseY out of drawCircle and eraseCircle and put that in timerDraw and timerErase instead.
Instead of calling your drawing code directly in timerDraw and timerErase, tell the view system that you need your view redrawn by calling setNeedsDisplay(). That will flag your view as needing to be redrawn and the view system will call your drawRect function again automatically as soon as it can.
Make your timers work again by overriding didMoveToSuperview and start them there; you should also add logic to stop them if they're already running.
Steps 1 and 3 are the critical bits that makes your error go away.
Something like this:
//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
}
}
As to the best way to achieve the animation you're attempting, you could look at just drawing the circle once and then, in your UIViewController moving the entire view on a timer. Or, possibly better, using Core Animation. Or, if your final product is going to be a game (or even game like), maybe take a look at Sprite Kit.