第一步、在需要导航栏透明的页面进行设置
//允许半透明状态
[self.navigationController.navigationBar setTranslucent:YES];
//画一张宽为屏幕宽，高为64的透明图片
UIColor *color = [UIColor clearColor];
CGRect rect = CGRectMake(0.0f, 0.0f, [UIScreen mainScreen].bounds.size.width, 64);
UIGraphicsBeginImageContext(rect.size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(context, [color CGColor]);
CGContextFillRect(context, rect);
UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
//将透明图片设为导航栏的背景图片
[self.navigationController.navigationBar setBackgroundImage:img forBarMetrics:UIBarMetricsDefault];
[self.navigationController.navigationBar setBackgroundColor:[UIColor clearColor]];
//对超出父视图的子视图不进行裁剪
self.navigationController.navigationBar.clipsToBounds = YES;
第二步、将导航栏改为不透明
[self.navigationController.navigationBar setTranslucent:NO];
CGRect rect = CGRectMake(0.0f, 0.0f, [UIScreen mainScreen].bounds.size.width, 64);
UIGraphicsBeginImageContext(rect.size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(context, [ColorRGB(41.0, 41.0, 41.0, 1) CGColor]);
CGContextFillRect(context, rect);
UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
[self.navigationController.navigationBar setBackgroundImage:img forBarMetrics:UIBarMetricsDefault];
self.navigationController.navigationBar.clipsToBounds = NO;
