半透明弹出选择窗时屏蔽导航栏

chooseView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, [DMDevceManager screenWidth], [DMDevceManager screenHeight])];

chooseView.backgroundColor = [[UIColor blackColor] colorWithAlphaComponent:0.75];
//以下方法来自cocoaChina的135790的回帖
UIWindow* currentWindow = [UIApplication sharedApplication].keyWindow;
[currentWindow addSubview:chooseView];