Modal View Controller displays blank first time, works properly subsequently

问题

I have a modal view controller that I am trying to present a web view in it. Tthe first time it appears, it shows up as blank. When I close it out and click it again, however, it displays fine. I'm thinking it may be an issue with the loading of the webView, but I've tried displaying it only when the webView finishes loading, but it never gets called then.

NSURL* newURL = [[NSURL alloc] initFileURLWithPath: fileString];
NSURLRequest *newURLRequest = [[NSURLRequest alloc] initWithURL: newURL];
[webViewController.webView loadRequest: newURLRequest];
[newURL release];
[newURLRequest release];
webViewController.modalPresentationStyle=UIModalPresentationPageSheet;
[self presentModalViewController:webViewController animated:YES];

回答1:

The webView control won't be accessible the first time until the first present call causes controls to be loaded and initialized. Before the first present, webViewController.webView will be nil and so calling loadRequest on it will do nothing.

You could move the loadRequest call after the presentModalViewController call.

But instead of accessing controls in view controller's views directly, it'd be better to declare the url string as a NSString property (called say urlString) in WebViewController and set it to fileString before the presentModalViewController call (and don't create the NSURL, etc there):

webViewController.urlString = fileString;
[self presentModalViewController:webViewController animated:YES];

Finally, in WebViewController, in viewWillAppear: or viewDidAppear:, create the NSURL (using urlString), create the NSURLRequest, and call loadRequest.

来源：https://stackoverflow.com/questions/4472824/modal-view-controller-displays-blank-first-time-works-properly-subsequently