Force a UIView to redraw immediately, instead of d

问题:

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.

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();

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.

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();

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

Any suggestions? Thanks!

回答1:

Try hiding the UI elements in a separate selector, and using the -performSelectorOnMainThread:withObject:waitUntilDone: method, using YES for the waitUntilDone argument. Then follow that up with another selector for screen capture.

回答2:

The update is done in the run loop.

Simply add :

self.toolbar.hidden = YES;

[[NSRunLoop currentRunLoop] runUntilDate: [NSDate dateWithTimeIntervalSinceNow: 0.01]];

CGImageRef screenCap = UIGetScreenImage();