1、iOS如何实现导航栏背景透明，但按钮保持不透明?
具体实现代码如下:
CGRect rect2 = [[UIScreen mainScreen] bounds];
CGSize size = rect2.size;
CGFloat width = size.width;
UIColor *color=[UIColor clearColor];
CGRect rect=CGRectMake(0, 0, width, 64);
UIGraphicsBeginImageContext(rect.size);
CGContextRef context=UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(context, [color CGColor]);
CGContextFillRect(context, rect);
UIImage *image=UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
[self.navigationController.navigationBar setBackgroundImage:image forBarMetrics:UIBarMetricsDefault];
self.navigationController.navigationBar.clipsToBounds=YES;
2、如何去掉导航栏下面那根线，如何修改背景色?
具体实现代码如下：
//去除背景
[self.navigationController.navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];
//消除阴影
self.navigationController.navigationBar.shadowImage = [UIImage new];
3、如何修改导航栏底部的横线颜色？
CGRect rect = CGRectMake(0, 0, self.view.bounds.size.width, 0.5);
UIGraphicsBeginImageContext(rect.size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextSetFillColorWithColor(context,[UIColor groupTableViewBackgroundColor].CGColor);
CGContextFillRect(context, rect);
UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
self.navigationController.navigationBar.shadowImage =img;
