• 場景模擬：
  點擊一個按鈕，彈出一個導航視圖。導航視圖中包含左按鈕：取消按鈕；右按鈕：存儲信息（什么亂起八糟的隨你）

• 出現(xiàn)問題：
  為導航視圖設置導航欄的左右按鈕后不顯示。

有一個UIViewController 和一個UINavigationController：

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

設置導航欄的左右按鈕：

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;

展現(xiàn)該導航視圖：

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

發(fā)現(xiàn)導航視圖并不現(xiàn)實左右按鈕，command+點擊 進入navigationItem查看其聲明和注釋：

@property(nonatomic,readonly,strong) UINavigationItem *navigationItem; // Created on-demand so that a view controller may customize its navigation appearance.```
大概意思是：在程序有需要時才創(chuàng)建，若有一個viewcontroller則可能屏蔽當前navigation中的item


* 解決方案：

將
` navigationController.navigationItem.leftBarButtonItem=leftButtonItem; navigationController.navigationItem.rightBarButtonItem=rightButtonItem;`
改為：
`
controller.navigationItem.leftBarButtonItem=leftButtonItem;
controller.navigationItem.rightBarButtonItem=rightButtonItem;
`
即可（本人不準確地理解為：UINavigationController并不具有view，因此需要擁有rootViewController即UIViewController,因此其外觀也被UIViewController所決定，所以需要設置UIViewController來設置NavigationController）。


* 貼上完整代碼：

-(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");
}

運行截圖：

![
![2.png](http://upload-images.jianshu.io/upload_images/2920598-43d6d75dda8354cb.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)](http://upload-images.jianshu.io/upload_images/2920598-407c584f1e8b4449.png?imageMogr2/auto-orient/strip%7CimageView2/2/w/1240)