iphone上面的风火轮

第一种方法：使用UIView and UIActivityIndicatorView

//创建UIWebView
WebView = [[UIWebView alloc] initWithFrame:CGRectMake(0, 44, 320, 400)];
[WebView setUserInteractionEnabled:NO];
[WebView setBackgroundColor:[UIColor clearColor]];
[WebView setDelegate:self];
[WebView setOpaque:NO];//使网页透明

NSString *path = @"http://www.baidu.com";
NSURL *url = [NSURL URLWithString:path];
[WebView loadRequest:[NSURLRequest requestWithURL:url]];

//创建UIActivityIndicatorView背底半透明View    
UIView *view = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 320, 480)];
[view setTag:103];
[view setBackgroundColor:[UIColor blackColor]];
[view setAlpha:0.8];
[self.view addSubview:view];

activityIndicator = [[UIActivityIndicatorView alloc] initWithFrame:CGRectMake(0.0f, 0.0f, 32.0f, 32.0f)];
[activityIndicator setCenter:view.center];
[activityIndicator setActivityIndicatorViewStyle:UIActivityIndicatorViewStyleWhite];
[view addSubview:activityIndicator];
[self.view addSubview:WebView];
[view release];
[WebView release];

//开始加载数据
- (void)webViewDidStartLoad:(UIWebView *)webView {    
      [activityIndicator startAnimating];         // 出现转轮
}

//数据加载完
- (void)webViewDidFinishLoad:(UIWebView *)webView {
     [activityIndicator stopAnimating];     //停止转轮
     UIView *view = (UIView *)[self.view viewWithTag:103];
     [view removeFromSuperview];
}

第二种方法：使用UIAlertView and UIActivityIndicatorView

//加载网页动画
- (void)webViewDidStartLoad:(UIWebView *)webView{
    if (myAlert==nil){        
       myAlert = [[UIAlertView alloc] initWithTitle:nil
                                                              message: @"正在讀取網路資料"
                                                                delegate: self
                                                 cancelButtonTitle: nil
                                                 otherButtonTitles: nil];

     UIActivityIndicatorView *activityView = [[UIActivityIndicatorView alloc] initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhite];
     activityView.frame = CGRectMake(120.f, 48.0f, 37.0f, 37.0f);
     [myAlert addSubview:activityView];  //把转轮嵌入到对话框中
     [activityView startAnimating];
     [myAlert show];
     }
}

- (void)webViewDidFinishLoad:(UIWebView *)webView{
      [myAlert dismissWithClickedButtonIndex:0 animated:YES];
}