ios 导航栏透明

1. 创建透明图片（新建继承NSObject 的ImageUtil类）

+ (UIImage*)imageWithColor:(UIColor*)color size:(CGFloat)size

{

    CGRect rect =CGRectMake(0.0f,0.0f, size, size);

    UIGraphicsBeginImageContext(rect.size);

    CGContextRef context =UIGraphicsGetCurrentContext();

    CGContextSetFillColorWithColor(context, [colorCGColor]);

    CGContextFillRect(context, rect);

    

    UIImage *theImage =UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return theImage;

}

2. 设置导航栏

UIImage *gradientImage44 = [ImageUtilimageWithColor:[UIColorcolorWithRed:1green:0blue:0alpha:0.5]size:1];

 UIImage *gradientImage32 = [ImageUtilimageWithColor:[UIColorcolorWithRed:1green:0blue:0alpha:0.5]size:1];

[[UINavigationBarappearance] setBackgroundImage:gradientImage44forBarMetrics:UIBarMetricsDefault];

    [[UINavigationBarappearance] setBackgroundImage:gradientImage32forBarMetrics:UIBarMetricsLandscapePhone];

    [[UINavigationBarappearance] setBarStyle:UIBarStyleDefault];

3.设置viewcontroller  放到viewDidLoad中

self.edgesForExtendedLayout =UIRectEdgeTop;