强制UIView立即重绘，而不是在下一个运行循环期间重绘

我创建了一个UIImagePicker /摄像头视图，其中包含一个用于拍摄快照的工具栏和自定义按钮。我不能真正改变使用默认方式，因为自定义按钮，我正在绘制视图顶部。

I've created a UIImagePicker / camera view, with a toolbar and custom button for taking a snapshot. I can't really change to using the default way because of the custom button, and I'm drawing on top of the view.

当你按下按钮时，我想用UIGetScreenImage（）拍摄截图;但是，即使我先隐藏它，工具栏也会显示在图像中：

When you hit the button, I want to take a screenshot using UIGetScreenImage(); however, the toolbar is showing up in the image, even if I hide it first:

//hide the toolbar
self.toolbar.hidden = YES; 

// capture the screen pixels
CGImageRef screenCap = UIGetScreenImage();

我很确定这是因为即使隐藏了工具栏，它也会在函数重绘后重新绘制返回并进入下一个运行循环 - 调用UIGetScreenImage后。

I'm pretty sure this is because even though the toolbar is hidden, it gets redrawn once the function returns and we enter the next run loop - after UIGetScreenImage is called.

我尝试进行以下添加，但没有帮助：

I tried making the following addition, but it didn't help:

//hide the toolbar
self.toolbar.hidden = YES; 
[self.toolbar drawRect:CGRectMake(0, 0, 320, 52)];

// capture the screen pixels
CGImageRef screenCap = UIGetScreenImage();

我也尝试使用setNeedsDisplay，但这也不起作用，因为再次抽奖发生在当前函数返回。

I also tried using setNeedsDisplay, but that doesn't work either because once again the draw happens after the current function returns.

有任何建议吗？谢谢！