UIActivityIndicatorView可以用於顯示某項工作在進行中，比如加載進度。在iphone中應用很廣泛

用法一：只顯示不停旋轉的進度滾輪指示器。
//顯示進度滾輪指示器
-(void)showWaiting {
 
progressInd=[[UIActivityIndicatorView alloc]initWithActivityIndicatorStyle:
  UIActivityIndicatorViewStyleWhiteLarge];
progressInd.center=CGPointMake(self.view.center.x,240);
[self.navigationController.view addSubview:progressInd];
[progressInd startAnimating];
}
//消除滾動輪指示器
-(void)hideWaiting
{
[progressInd stopAnimating];
}





用法二：帶有半透明背景的進度輪指示器。

 
//顯示進度滾輪指示器
-(void)showWaiting:(UIView *)parent {
 
    int width = 32, height = 32;
   
    CGRect frame = CGRectMake(100, 200, 110, 70) ;//[parent frame]; //[[UIScreen mainScreen] applicationFrame];
    int x = frame.size.width;
    int y = frame.size.height;
   
    frame = CGRectMake((x - width) / 2, (y - height) / 2, width, height);
    UIActivityIndicatorView* progressInd = [[UIActivityIndicatorView alloc]initWithFrame:frame];
    [progressInd startAnimating];
    progressInd.activityIndicatorViewStyle = UIActivityIndicatorViewStyleWhiteLarge;
   
frame = CGRectMake((x - 70)/2, (y - height) / 2 + height, 80, 20);
UILabel *waitingLable = [[UILabel alloc] initWithFrame:frame];
waitingLable.text = @"Loading...";
waitingLable.textColor = [UIColor whiteColor];
waitingLable.font = [UIFont systemFontOfSize:15];
waitingLable.backgroundColor = [UIColor clearColor];
 
    frame =  CGRectMake(100, 200, 110, 70) ;//[parent frame];
    UIView *theView = [[UIView alloc] initWithFrame:frame];
    theView.backgroundColor = [UIColor blackColor];
    theView.alpha = 0.7;
   
    [theView addSubview:progressInd];
[theView addSubview:waitingLable];
   
    [progressInd release];
[waitingLable release];
   
    [theView setTag:9999];
    [parent addSubview:theView];
    [theView release];
}

//消除滾動輪指示器
-(void)hideWaiting
{
    [[self.view viewWithTag:9999] removeFromSuperview];
}