IOS:ActivityIndi​​cator超过UITableView ......怎么样？

Question

我希望在加载数据时(在另一个线程中)在uitableview上显示活动指示器.所以在UITableViewController的ViewDidLoad方法中:

-(void)viewDidLoad
 {
    [super viewDidLoad];

    //I create the activity indicator
    UIActivityIndicatorView *ac = [[UIActivityIndicatorView alloc]  
                      initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleGray];
    [ac startAnimating];

    //Create the queue to download data from internet
    dispatch_queue_t downloadQueue = dispatch_queue_create("PhotoDownload",NULL); 
    dispatch_async(downloadQueue, ^{
      //Download photo
      .......
      .......
      dispatch_async(dispatch_get_main_queue(), ^{
         ......
         ......
         [ac stopAnimating];
      });
    });
   .......

为什么活动指示器不会显示在表格视图上？我怎样才能实现它？

Answer 1

您需要添加UIActivityIndi​​catorView.您可以将其添加到UITableView标头视图中.为此,您需要提供自己的自定义视图.

...
UIView *view = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 320, 50)];
[view addSubview:ac]; // <-- Your UIActivityIndicatorView
self.tableView.tableHeaderView = view;
...

Answer 2

我一直试图找到解决方案,并阅读了很多论坛,但我没有得到我想要的.在了解了活动指示器和表视图控制器如何工作之后,我提出了以下解决方案.

出于某种原因,如果您尝试使用tableReload或任何其他昂贵的进程在同一线程上启动活动指示器,则活动指示器永远不会运行.如果您尝试在另一个线程中运行表重新加载或其他操作,那么它可能不安全并可能产生错误或不需要的结果.所以我们可以运行在另一个线程上显示活动指示符的方法.

我还将此解决方案与MBProgressHUD结合使用,以呈现出具有活动指示器的视图更好看的内容.无论如何,可以自定义activityView的外观.

-(void)showActivityViewer
{
    AppDelegate *delegate = [[UIApplication sharedApplication] delegate];
    UIWindow *window = delegate.window;
    activityView = [[UIView alloc] initWithFrame: CGRectMake(0, 0, window.bounds.size.width, window.bounds.size.height)];
    activityView.backgroundColor = [UIColor blackColor];
    activityView.alpha = 0.5;

    UIActivityIndicatorView *activityWheel = [[UIActivityIndicatorView alloc] initWithFrame: CGRectMake(window.bounds.size.width / 2 - 12, window.bounds.size.height / 2 - 12, 24, 24)];
    activityWheel.activityIndicatorViewStyle = UIActivityIndicatorViewStyleWhite;
    activityWheel.autoresizingMask = (UIViewAutoresizingFlexibleLeftMargin |
                                      UIViewAutoresizingFlexibleRightMargin |
                                      UIViewAutoresizingFlexibleTopMargin |
                                      UIViewAutoresizingFlexibleBottomMargin);
    [activityView addSubview:activityWheel];
    [window addSubview: activityView];

    [[[activityView subviews] objectAtIndex:0] startAnimating];
}

-(void)hideActivityViewer
{
    [[[activityView subviews] objectAtIndex:0] stopAnimating];
    [activityView removeFromSuperview];
    activityView = nil;
}

- (IBAction)reloadDataAction:(id)sender {
    [NSThread detachNewThreadSelector:@selector(showActivityViewer) toTarget:self withObject:nil];  
    //... do your reload or expensive operations
    [self hideActivityViewer];
}

Answer 3

[iOS 5 +]
如果您只想在没有附加父视图的情况下显示activityWheel,您还可以将activityWheel直接添加到tableView并使用tableViews contentOffset计算框架的y值:

@interface MyTableViewController ()
@property (nonatomic, strong) UIActivityIndicatorView *activityView;
@end

// ....

- (void) showActivityView {
    if (self.activityView==nil) {
        self.activityView = [[UIActivityIndicatorView alloc] initWithFrame:CGRectZero];
        [self.tableView addSubview:self.activityView];
        self.activityView.activityIndicatorViewStyle = UIActivityIndicatorViewStyleWhiteLarge;
        self.activityView.hidesWhenStopped = YES;
        // additional setup...
        // self.activityView.color = [UIColor redColor]; 
    }
    // Center 
    CGFloat x = UIScreen.mainScreen.applicationFrame.size.width/2;
    CGFloat y = UIScreen.mainScreen.applicationFrame.size.height/2;
    // Offset. If tableView has been scrolled
    CGFloat yOffset = self.tableView.contentOffset.y;
    self.activityView.frame = CGRectMake(x, y + yOffset, 0, 0);

    self.activityView.hidden = NO;
    [self.activityView startAnimating];
}

- (void) hideActivityView {
    [self.activityView stopAnimating];
}

如果activityView没有立即显示(或从不显示),请参阅zirinisp的答案或在后台执行繁重的工作.