ios在navigation上添加loading(UIActivityIndicatorView)按钮

// initing the loading view
  CGRect frame = CGRectMake(0.0, 0.0, 25.0, 25.0);
  UIActivityIndicatorView *loading = [[UIActivityIndicatorView alloc] initWithFrame:frame];
  [loading startAnimating];
  loading.autoresizingMask = (UIViewAutoresizingFlexibleLeftMargin |
                UIViewAutoresizingFlexibleRightMargin |
                UIViewAutoresizingFlexibleTopMargin |
                UIViewAutoresizingFlexibleBottomMargin);

  // initing the bar button
  UIBarButtonItem *loadingView = [[UIBarButtonItem alloc] initWithCustomView:loading];

  loadingView.target = self;

  self.navigationItem.rightBarButtonItem = loadingView;