iOS 设置UINavtionController navigationBar 为透明颜色

 //设置背景颜色

    if ([self.navigationController.navigationBarrespondsToSelector:@selector( setBackgroundImage:forBarMetrics:)]){

        NSArray *list=self.navigationController.navigationBar.subviews;

        for (id objin list) {

            if ([obj isKindOfClass:[UIImageViewclass]]) {

                UIImageView *imageView=(UIImageView *)obj;

                imageView.hidden=YES;

            }

        }

        UIImageView *imageView=[[UIImageViewalloc] initWithFrame:CGRectMake(0, -20,420, 64)];

        imageView.image=[UIImageimageNamed:@"clear"];

        [self.navigationController.navigationBaraddSubview:imageView];

        [self.navigationController.navigationBarsendSubviewToBack:imageView];

        self.navigationController.navigationBar.backgroundColor = [UIColorclearColor];

        

    }