iOS UINavigationController 添加导航栏

• 场景模拟：
  点击一个按钮，弹出一个导航视图。导航视图中包含左按钮：取消按钮；右按钮：存储信息（什么乱起八糟的随你）

• 出现问题：
  为导航视图设置导航栏的左右按钮后不显示。

有一个UIViewController 和一个UINavigationController：

UIViewController* controller = [[UIViewController alloc]init];
 UINavigationController* navigationController = [[UINavigationController alloc]initWithRootViewController:controller];

设置导航栏的左右按钮：

UIBarButtonItem* leftButtonItem = [[UIBarButtonItem alloc]initWithBarButtonSystemItem:UIBarButtonSystemItemCancel target:self action:@selector(clickCancel)];
    UIBarButtonItem* rightButtonItem = [[UIBarButtonItem alloc]initWithBarButtonSystemItem:UIBarButtonSystemItemSave target:self
    action:@selector(clickSave)];
navigationController.navigationItem.leftBarButtonItem=leftButtonItem; navigationController.navigationItem.rightBarButtonItem=rightButtonItem;

展现该导航视图：

[self presentViewController:navigationController animated:YES completion:nil];

发现导航视图并不现实左右按钮，command+点击 进入navigationItem查看其声明和注释：

@property(nonatomic,readonly,strong) UINavigationItem *navigationItem; // Created on-demand so that a view controller may customize its navigation appearance.```
大概意思是：在程序有需要时才创建，若有一个viewcontroller则可能屏蔽当前navigation中的item


* 解决方案：

将
` navigationController.navigationItem.leftBarButtonItem=leftButtonItem; navigationController.navigationItem.rightBarButtonItem=rightButtonItem;`
改为：
`
controller.navigationItem.leftBarButtonItem=leftButtonItem;
controller.navigationItem.rightBarButtonItem=rightButtonItem;
`
即可（本人不准确地理解为：UINavigationController并不具有view，因此需要拥有rootViewController即UIViewController,因此其外观也被UIViewController所决定，所以需要设置UIViewController来设置NavigationController）。


* 贴上完整代码：

-(IBAction)click:(id)sender {
UIViewController* controller = [[UIViewController alloc]init];
UINavigationController* navigationController = [[UINavigationController alloc]initWithRootViewController:controller];
UIBarButtonItem* leftButtonItem = [[UIBarButtonItem alloc]initWithBarButtonSystemItem:UIBarButtonSystemItemCancel target:self action:@selector(clickCancel)];
UIBarButtonItem* rightButtonItem = [[UIBarButtonItem alloc]initWithBarButtonSystemItem:UIBarButtonSystemItemSave target:self
action:@selector(clickSave)];
controller.title=@"damn";
controller.navigationItem.leftBarButtonItem=leftButtonItem;
controller.navigationItem.rightBarButtonItem=rightButtonItem;
[navigationController.view setBackgroundColor:[UIColor whiteColor]];
[self presentViewController:navigationController animated:YES completion:nil];
}
-(void)clickCancel{
[self dismissViewControllerAnimated:YES completion:nil];
}
-(void)clickSave{
NSLog(@"save successfully");
}

运行截图：

![
![2.png](https://img.haomeiwen.com/i2920598/43d6d75dda8354cb.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)](https://img.haomeiwen.com/i2920598/407c584f1e8b4449.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)