iOS: can I take screenshot on global queue?

Question

I wonder how can I take a screenshot in a global queue? right now I'm doing it in the main queue and it works, if I do it in the global queue, things freeze. I'm using this screenshot code: iOS: what's the fastest, most performant way to make a screenshot programmatically? I also tried the following code to take the snapshot of self.view, but it also doesn't work:

+(UIImage *)snapshot_of_view:(UIView*)view {
    UIGraphicsBeginImageContextWithOptions(view.bounds.size, NO, [UIScreen mainScreen].scale);
    [view.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image;
}

any ideas?

score 1 · Accepted Answer · answered Apr 16 '15 at 22:03

1

Any UI operation MUST be performed in the main thread.

answered Apr 16 '15 at 22:03

Matteo Gobbi

17,697
3
27
41

I saw this post (http://stackoverflow.com/questions/11528803/is-uigraphicsbeginimagecontext-thread-safe) say that UIGraphicsBeginImageContext is thread safe, does that mean I can do UI..context on any thread? – ios learner Apr 22 '15 at 19:54

score 0 · Answer 2 · answered Apr 16 '15 at 22:06

You are calling user interface code. UI code must be on the main thread, since that thread has the main run loop and stuff.

You need to do it on the main thread:

+(UIImage *)snapshot_of_view:(UIView*)view {
    dispatch_async(dispatch_get_main_queue(), ^{
        UIGraphicsBeginImageContextWithOptions(view.bounds.size, NO, [UIScreen mainScreen].scale);
        [view.layer renderInContext:UIGraphicsGetCurrentContext()];
        UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        return image;
    });
}

iOS: can I take screenshot on global queue?

2 Answers2