SVProgressHUD源码记二:要点学习

如何表示弃用的API

  + (void)showWithMaskType:(SVProgressHUDMaskType)maskType __attribute__((deprecated("Use show and setDefaultMaskType: instead.")));

使用 __attribute__, deprecated 关键字表示已过时的API

单例创建方式

    static dispatch_once_t once;
    static SVProgressHUD *sharedView;
    dispatch_once(&once, ^{
      sharedView = [[self alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
      });
    return sharedView;

使用GCD的dispatch_once函数

数组元素的倒序遍历

    NSEnumerator *frontToBackWindows = [UIApplication.sharedApplication.windows reverseObjectEnumerator];
    for (UIWindow *window in frontToBackWindows){
        BOOL windowOnMainScreen = window.screen == UIScreen.mainScreen; // 为设备屏幕
        BOOL windowIsVisible = !window.hidden && window.alpha > 0;
        BOOL windowLevelNormal = window.windowLevel == UIWindowLevelNormal;
        
        if(windowOnMainScreen && windowIsVisible && windowLevelNormal){
            [window addSubview:self.overlayView];
            break;
        }
    }

枚举器,反向遍历reverseObjectEnumerator;
objectEnumerator为正向遍历,返回NSEnumerator