为什么在调用方法stringByEvaluatingJavaScriptFromString时以下Objective-C代码会停止？

Question

I use the following Objective-C code in my iPhone App:

NSLog(@"Before JS string definition");
NSString* jsString = [NSString stringWithFormat:@"alert('ok');"];
NSLog(@"Before JS call");
@try {
    [self.viewController.webView stringByEvaluatingJavaScriptFromString:jsString];
}
@catch (id theException) {
    NSLog(@"%@", theException);
}
NSLog(@"JS call string was: %@", jsString);

When I run it, I get in the logs:

2012-12-13 16:10:34.743 MyApp.com[2328:907] Before JS string definition
2012-12-13 16:10:34.744 MyApp.com[2328:907] Before JS call

So, the last NSLog call doesn't get executed. Obviously the call to stringByEvaluatingJavaScriptFromString somehow hangs there. No error message in the logs. No exception. Nothing.

What's going on? How can I debug this?

Answer 1

I would expect that alert() is a synchronous call and will not return until after the user has dismissed the message box. The method to evaluate JavaScript will not return until after the JavaScript has finished.

Answer 2

I can't see how can you benefit from this code (don't see the purpose, you could generate your own alerts, only if you have some complex javascript logic over just a simple and straight alert();). But note that stringByEvaluatingJavaScriptFromString has a limitation of 10secs for execution and 10mb of ram. Maybe something here is the issue, but as far as I could remember it gives an error to the log of some kind if these restrictions met.