UIWebView stringByEvaluatingJavaScriptFromString hangs on iOS5.0/5.1 when called using GCD

Question

I have the following code in viewDidLoad, which works properly on iOS 4.3, but it hangs on iOS 5/5.1. On iOS 5/5.1, the alert dialog is shown but can not be dismissed, the UI thread freezes, the OK button just can not be clicked.

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    dispatch_sync(dispatch_get_main_queue(), ^{
        [self.webview stringByEvaluatingJavaScriptFromString:@"alert('HELLO WORLD!')"];
    });
});

Is this a bug?

Answer 1

After test, I consider it as a Bug, and changing code to use

[webView performSelectorOnMainThread:@selector(stringByEvaluatingJavaScriptFromString:) withObject:js waitUntilDone:NO]

will solve it.