Gradient turns to black - ios

Question

I am using gradient in subview of UIView, after coming back to app by switching from some apps, the gradient becomes black. Don't know why, If anybody out there knows anything about this, help me out here.
Also i didn't subclass it programatically , directly put that in the UIView's class place in Storyboard itself (CustomGradientBlueView). Is that can be an issue.?
This is the code which am using for gradient ->
import UIKit
class CustomGradientBlueView: UIView {
required init(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
}
override init(frame: CGRect) {
super.init(frame: frame)
}
override func drawRect(rect: CGRect) {
let context = UIGraphicsGetCurrentContext()
// colour declarations
let gradientColor1 = UIColor(red: 0.361, green: 0.145, blue: 0.553, alpha: 1.000)
let gradientColor2 = UIColor(red: 0.263, green: 0.537, blue: 0.635, alpha: 1.000)
// gradient decalarations
let gradient = CGGradientCreateWithColors(CGColorSpaceCreateDeviceRGB(), [gradientColor1.CGColor,gradientColor2.CGColor], [0,1])
//rectangle drawing
var screen = UIScreen.mainScreen().bounds.size
let rectanglePath = UIBezierPath(rect: CGRectMake(0,0, screen.width, screen.height))
CGContextSaveGState(context)
rectanglePath.addClip()
CGContextDrawLinearGradient(context, gradient, CGPointMake(0,0 ), CGPointMake(screen.width, screen.height), 0)
}
}

Answer 1

The problem is likely in these lines:
var screen = UIScreen.mainScreen().bounds.size
let rectanglePath = UIBezierPath(rect: CGRectMake(0,0, screen.width, screen.height))
CGContextSaveGState(context)
rectanglePath.addClip()
You are calling CGContextSaveGState without calling CGContextRestoreGState to balance it. That is very dangerous. If the context is maintained, which is perfectly possible, then you are saying addClip again with your previous clipping path already still in place - because you did not remove it with a balancing CGContextRestoreGState after drawing. Because of the nature of clipping paths, this causes you to end up with your whole view clipping, and your drawing is completely suppressed — hence the black view.
(It is not at all clear what you think you are doing with this clipping path in any case. There is no need to clip to the screen bounds, and accessing the screen bounds inside a view's drawRect: is a very odd thing to do. You might be happier just deleting those four lines altogether.)