去掉导航栏底线

发现之前用创建一个空image赋值给UINavigationBar的shadowImage的方法不管用，那就给UINavigationBar的shadowImage设置一个透明的image或者和导航栏一样颜色的图片。代码如下：

// 创建一个UINavigationBar的category，实现以下方法：
//宏定义宽高
#define NavBar_width [UIScreen mainScreen].bounds.size.width
#define NavBar_height 1
//用导航栏图片设置
-(void)clearShadowImageWithImage:(UIImage*)image {
    
    UIGraphicsBeginImageContext(CGSizeMake(NavBar_width, NavBar_height));
    
    [image drawInRect:CGRectMake (0, 0, NavBar_width, NavBar_height)];
    
    image = UIGraphicsGetImageFromCurrentImageContext();
    
    UIGraphicsEndImageContext ();
    
    self.shadowImage = image;
}

//用导航栏颜色设置
- (void)clearShadowImageWithColor:(UIColor*)color {
    self.shadowImage = [self imageWithColor:color];
}
- (UIImage*)imageWithColor:(UIColor*)color {
    if (!color) color = [UIColor clearColor];
    
    UIGraphicsBeginImageContext(CGSizeMake(NavBar_width, NavBar_height));
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetFillColorWithColor(context, [color CGColor]);
    CGContextFillRect(context, CGRectMake (0 ,0 , NavBar_width, NavBar_height));
    UIImage *theImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return theImage;
}