/* Adding the Path */
UserGraphBuff = UIGraphicsGetCurrentContext();
CGContextSetRGBStrokeColor(UserGraphBuff,5,10,0,1);
CGContextSetLineWidth(UserGraphBuff, 2 );
CGContextBeginPath(UserGraphBuff);
//line to last user point
CGContextAddLineToPoint(UserGraphBuff, (*xVal)[sizeof xVal / sizeof *xVal - 1], (*yNewVal)[sizeof yNewVal / sizeof *yNewVal - 1]);
//line to rest of user points in reverse order
for (int i = sizeof xVal / sizeof *xVal - 1; i > -1; i--){
CGContextAddLineToPoint(UserGraphBuff, (*xVal)[i], (*yNewVal)[i]);
}
//EOFill
CGContextEOFillPath(UserGraphBuff);
Above is the code I am trying to work through. Its supposed to do what CGContext says it does but I am not getting any thing drawn. I keep getting this error:
Fri Oct 28 13:18:40 case.app testApplication[4127] <Error>: CGContextSetRGBStrokeColor: invalid context 0x0
Fri Oct 28 13:18:40 case.app testApplication[4127] <Error>: CGContextSetLineWidth: invalid context 0x0
Fri Oct 28 13:18:40 case.app testApplication[4127] <Error>: CGContextBeginPath: invalid context 0x0
Fri Oct 28 13:18:40 case.app testApplication[4127] <Error>: CGContextAddLineToPoint: invalid context 0x0
Fri Oct 28 13:18:40 case.app testApplication[4127] <Error>: CGContextDrawPath: invalid context 0x0
I reference the CGContextRef in my header file.
i don't think i understand CGContext well enough nor do i know what CGContextRef should be.
For your code to work, it needs to be executed in the drawRect
method of your UIView
subclass (and you don't call drawRect
directly - this is called by the OS when it needs the UIView to render itself). You're presumably trying to run this code from a touch event or from viewDidLoad
or something like that.
来源:https://stackoverflow.com/questions/7932654/invalid-context-0x0-error-when-using-cgcontext-functions