swift - 从后台操作在 NSView 中绘制无效

Question

我试图从后台操作绘制到 NSView，但没有看到任何效果。

let queue = OperationQueue()
queue.addOperation() {
  doTheBackgroundStuff()
}

启动后台操作，进行大量计算。在我的 AppDelegate 中

@IBOutlet weak var image: NSImageView!  // some image to show
@IBOutlet weak var number: NSTextField! // a corresponding number
@IBOutlet weak var mainView: NSView!    // the main view holding the above

作业

number.intValue = Int32(someNumber)

定期(经常)从后台操作发出。但文本永远不会改变。我已经在 IB 中为 View 和 TextField 设置了“可以同时绘制”。我也试过了

if mainView.lockFocusIfCanDraw() {
  mainView.setNeedsDisplay(mainView.rectPreservedDuringLiveResize)
  mainView.unlockFocus()
}

在文本字段分配之后。也无济于事。

Answer 1

按照 https://stackoverflow.com/a/19997698/3419541 中的描述调用 flushGraphics :

I read about NSGraphicsContext Restriction at Thread guide.

Here, I found the following line:

If you do any drawing from a secondary thread, you must flush your drawing calls manually. Cocoa does not automatically update views with content drawn from secondary threads, so you need to call the flushGraphics method of NSGraphicsContext when you finish your drawing. If your application draws content from the main thread only, you do not need to flush your drawing calls.