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;