一、设置导航栏底线

1. 简单获取底线

- (UIView *)navLine {
    if (!_navLine) {
        UIView *backgroundView = [self.navigationController.navigationBar subviews].firstObject;
        _navLine = backgroundView.subviews.firstObject;        
    }
    return _navLine;
}

2.单个页面设置隐藏显示

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    self.navLine.hidden = YES;
}

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];
    self.navLine.hidden = NO;    
}

二、设置导航栏背景图
1.设置导航栏背景图所需的各个尺寸
1倍图 640 * 128 px (一般用不到)
2倍图 750 * 128 px (5s，6，6s, 7)
3倍图 1242*192 px (6p, 6sp)
备注：其实一般两种图就足够，5s也是用2倍图，现在一般最低适配到5s，当然如果需求不一样就三张。

设置导航背景图代码

/*设置图片拉伸范围 如果图片被挤压变形的情况下*/
   UIImage *backImage = [UIImage imageNamed:@"homeNav"]; 
   backImage = [backImage resizableImageWithCapInsets:UIEdgeInsetsMake(0, 100, 10, 10)];

/*设置背景图*/
   [self.navigationController.navigationBar setBackgroundImage:backImage forBarMetrics:UIBarMetricsDefault];

设置导航条背景图片时有时self.view会向下偏移64像素

//此句代码解决坐标问题

[self.navigationController.navigationBar setTranslucent:YES];

//当translucent = YES，controller中self.view的原点是从导航栏左上角开始计算

//当translucent = NO，controller中self.view的原点是从导航栏左下角开始计算

设置导航栏背景纯色

   UINavigationBar *bar = [UINavigationBar appearance];
   bar.barTintColor = [UIColor colorWithRed:62/255.0 green:173/255.0 blue:176/255.0 alpha:1.0];

设置导航栏title字体类型和大小

 [self.navigationController.navigationBar setTitleTextAttributes:@{
                                                                      NSFontAttributeName:[UIFont fontWithName:@"Helvetica-Bold" size:22],
                                                                      NSForegroundColorAttributeName:[UIColor whiteColor]
                                                                      }];

设置导航栏透明

- (void)viewWillAppear:(BOOL)animated {
    
    [super viewWillAppear:animated];
    
    [self.navigationController.navigationBar setBackgroundImage:[UIImage new] forBarMetrics:UIBarMetricsDefault];    
    [self.navigationController.navigationBar setShadowImage:[UIImage new]];
    
}

- (void)viewWillDisappear:(BOOL)animated {
    
    [super viewWillDisappear:animated];
    
    [self.navigationController.navigationBar setBackgroundImage:nil forBarMetrics:UIBarMetricsDefault];``    
    [self.navigationController.navigationBar setShadowImage:nil];
}