向左箭头- UINavigationItem

Question

我找遍了，但我似乎找不到。我相信很多人都会有我的链接，我很可能已经看过了。但如果有人能给我看一下做以下事情的代码：

我希望在我的UINavigationBar中有一个左箭头作为"Back“UINavigationItem。我该怎么做呢？下面是我的UIViewController中的当前代码

theBar = [[UINavigationBar alloc] initWithFrame:CGRectMake(0.0f, 0.0f, 320.0f, 48.0f)];

UIBarButtonItem *leftButton = [[UIBarButtonItem alloc] initWithTitle:@"Back" style:UIBarButtonItemStyleBordered target:nil action:@selector(backButtonSelected:)];

UIBarButtonItem *rightButton = [[UIBarButtonItem alloc] initWithTitle:@"Options" style:UIBarButtonItemStyleBordered target:nil action:@selector(optionsButtonSelected:)];

UINavigationItem *item = [[UINavigationItem alloc] initWithTitle:@"Title"];
item.leftBarButtonItem = leftButton;
item.hidesBackButton = YES;
item.rightBarButtonItem = rightButton;

[self.view addSubview:theBar];

Answer 1

为了在屏幕上弹出/推送UIViewControllers，您应该使用UINavigationController。导航控制器会自动将UINavigationBar添加到您的UIViewControllers中，因此您不需要像以前那样创建它们。

这是一个示例。我没有寻找内存泄漏。在应用程序委托中，您可以找到此方法：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{        
    // Override point for customization after application launch.
    MainVC *mainVC = [[MainVC alloc] init];
    UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController:mainVC];
    [self.window addSubview:navController.view];
    [self.window makeKeyAndVisible];

    return YES;
}

MainVC是表示层次结构的级别1的UIViewController。我在里面有

- (void)loadView
{
    self.view = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 320, 480)];
    self.view.backgroundColor = [UIColor redColor];
    self.title = @"MainVC";

    UIBarButtonItem *rightButton = [[UIBarButtonItem alloc] initWithTitle:@"SecondLevel" style:UIBarButtonItemStyleBordered target:self action:@selector(secondLevelSelected:)];
    self.navigationItem.rightBarButtonItem = rightButton;
}

- (void) secondLevelSelected:(id)sender
{
    SecondVC *secondVC = [[SecondVC alloc]  init];
    [self.navigationController pushViewController:secondVC animated:YES];
}

SecondVC是另一个表示层次结构第二级的UIViewController。在这里你会找到你想要的后退按钮。

- (void)loadView
{
    self.view = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 320, 240)];
    self.view.backgroundColor = [UIColor greenColor];
    self.title = @"SecondVC";

    self.navigationItem.hidesBackButton = YES;
    UIBarButtonItem *leftBtn = [[UIBarButtonItem alloc] initWithTitle:@"FirstLevel" style:UIBarButtonItemStyleBordered target:self action:@selector(leftBtnSelected:)];
    self.navigationItem.leftBarButtonItem = leftBtn;
}

- (void) leftBtnSelected:(id)sender
{
    [self.navigationController popViewControllerAnimated:YES];
}

Answer 2

我想这可能就是你要找的。

// in .h file
@property (nonatomic, retain) UINavigationBar *navBar;

// in .m file just below @implementation
@synthesize navBar;


// within .m method
navBar = [[UINavigationBar alloc] initWithFrame:CGRectMake(0.0f, 0.0f, 320.0f, 48.0f)];
navBar.barStyle = UIBarStyleBlack;

UINavigationItem *title = [[UINavigationItem alloc] initWithTitle:@"Nav Bar Title"];

UIBarButtonItem *leftButton = [[UIBarButtonItem alloc] 
                       initWithTitle:@"Back" 
                               style:UIBarButtonItemStylePlain 
                              target:nil
                              action:@selector(backButtonSelected:)];

title.leftBarButtonItem = leftButton; 

UIBarButtonItem *rightButton = [[UIBarButtonItem alloc] 
         initWithBarButtonSystemItem:UIBarButtonSystemItemAction
                              target:nil
                              action:@selector(showActionSheet:)];

title.rightBarButtonItem = rightButton;

[navBar pushNavigationItem:title animated:YES];

[self.view addSubview:navBar];