1.實現(xiàn)父視圖半透明效果硬爆，子視圖不透明爸黄，在父視圖上設置：
myView.backgroundColor=[[UIColor blackColor] colorWithAlphaComponent:0.5];
2.實現(xiàn)半透明視圖覆蓋導航欄和狀態(tài)欄效果（只能將視圖添加到Window）：
[[[UIApplication sharedApplication] keyWindow]addSubview:myView];
https://blog.csdn.net/yibuyibulai/article/details/45078275
第一種：背景透明覆蓋導航欄
NextViewController *vc = [[NextViewController alloc] init]; vc.view.backgroundColor = [UIColor colorWithRed:0 green:0 blue:0 alpha:.5]; vc.modalPresentationStyle = UIModalPresentationOverFullScreen;[self presentViewController:vc animated:YES completion:nil];
第二種：背景透明不覆蓋導航欄
NextViewController *vc = [[NextViewController alloc] init];self.definesPresentationContext = YES;vc.view.backgroundColor = [UIColor colorWithRed:0 green:0 blue:0 alpha:.5];vc.modalPresentationStyle = UIModalPresentationOverCurrentContext;[self presentViewController:vc animated:YES completion:nil];
第三種：不透明且覆蓋導航欄
NextViewController *vc = [[NextViewController alloc] init];[self presentViewController:vc animated:YES completion:nil];
https://blog.csdn.net/weixin_34237596/article/details/87122124
