I will be very short:
I'am drawing lines using drawrect and NSBezierPath.
To draw these lines I am using a for loop.
Now, since the loop takes many seconds,I'm trying to use a NSProgresIndicator to show the progress and to update it within the loop I used dispatch_async & queue.. The ProgressIndicator updates but nothing is being drawn.. If don't use the queue the lines are drawn but the indicator updates at the end of the cycle.
What am I doing wrong ?
The error:
<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.
// SAMPLE OF CODE
dispatch_queue_t myQueue = dispatch_queue_create("my queue", NULL);
dispatch_async(myQueue, ^
{
for (int i = 1; i <= 200; i++) {
dispatch_async(dispatch_get_main_queue(), ^{
[istance set_progress:i];
//This sets the progress, but bezierPath doesn't work
});
//Bezier already alloc & init
[my_path moveToPoint....]
[my_path lineToPoint....]
[my_path stroke]
}
});
In general you shouldn't be drawing on a background thread or queue.
Please read this document for information about multithreaded drawing. Skip to "Drawing Restrictions"