UIView添加一個分類。

#import <UIKit/UIKit.h>

@interface UIView (SWLExtension)

/**
 * 判斷一個控件是否真正顯示在主窗口
 */
- (BOOL)isShowingOnKeyWindow;

@end

- (BOOL)isShowingOnKeyWindow
{
    // 主窗口
    UIWindow *keyWindow = [UIApplication sharedApplication].keyWindow;
    
    // 以主窗口左上角為坐標原點, 計算self的矩形框
    CGRect newFrame = [keyWindow convertRect:self.frame fromView:self.superview];
    CGRect winBounds = keyWindow.bounds;
    
    // 主窗口的bounds 和 self的矩形框 是否有重疊
    BOOL intersects = CGRectIntersectsRect(newFrame, winBounds);
    
    return !self.isHidden && self.alpha > 0.01 && self.window == keyWindow && intersects;
}