导航栏的设置 背景 线

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

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

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

/*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];

[self.navigationController.navigationBar setTranslucent:YES];

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

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

- (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];
}