Loading效果 UIActivityIndicatorView

//初始化:
UIActivityIndicatorView* indicator = [[UIActivityIndicatorView alloc] initWithFrame:CGRectMake(0, 0, 50, 50)];

//設置顯示樣式,見UIActivityIndicatorViewStyle的定義
indicator.activityIndicatorViewStyle = UIActivityIndicatorViewStyleWhiteLarge;

//設置顯示位置
[indicator setCenter:CGPointMake(self.frame.size.width / 2, self.frame.size.height / 2)];

//設置背景色
indicator.backgroundColor = UIColor.gray.

//設置背景透明
indicator.alpha = 0.5;

//設置背景為圓角矩形
indicator.layer.cornerRadius = 6;
indicator.layer.masksToBuounds = YES;

//將初始化好的indicator add到view中
[view addSubView:indicator];

//開始顯示Loading動畫
[indicator startAnimating];

//停止顯示Loading動畫
[indicator stopAnimating];