UIWebView：在导航栏中添加进度条

Question

我是iOS开发的新手。在UIWebView中，我想在导航栏中添加进度条。

图像：

NSString *urlAddress = @"http://www.facebook.com";
[self.navigationController.navigationBar
 setTitleTextAttributes:@{NSForegroundColorAttributeName : [UIColor blackColor]}];

UIBarButtonItem *cancel = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemStop target:self action:@selector(cancelAction:)];

self.navigationItem.rightBarButtonItem = cancel;
self.navigationItem.title =urlAddress;