DrawRect和NSProgressIndicator

Question

我将非常简短：

我正在用drawrect和NSBezierPath绘制线条。

为了绘制这些线，我使用了for循环。

现在，由于循环需要很多秒，所以我尝试使用NSProgresIndicator来显示进度，并在我使用dispatch_async &queue的循环中更新它。ProgressIndicator更新，但没有绘制任何内容。如果不使用队列，则绘制行，但指示符在周期结束时更新。

我做错什么了？

错误：

<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]

}
               });

Answer 1

通常，您不应该在后台线程或队列上绘图。

有关多线程绘图的信息，请阅读此文档。跳到“绘图限制”

https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/Multithreading/ThreadSafetySummary/ThreadSafetySummary.html