Ios 按右栏按钮项目可移动左栏按钮项目

我的web视图导航栏上有三个左栏按钮项。一个可以返回到我的应用程序菜单以及后退和前进按钮的按钮。我有一个右栏按钮，可以打开活动视图控制器。当我按下右侧按钮时，左侧的前进和后退按钮向下移动并脱离导航栏

- (void)viewDidLoad
{   
    leftBarButtonItems = [NSArray arrayWithObjects:@"Menu", @"Back", @"Forward", nil];

    [super viewDidLoad];
    // Do any additional setup after loading the view from its nib.
    NSString *urlAddress = @"http://www.littleheartrecords.com/releases.html";
    NSURL *url = [NSURL URLWithString:urlAddress];
    NSURLRequest *requestObj = [NSURLRequest requestWithURL:url];
    [webView loadRequest:requestObj];

    UIBarButtonItem *systemAction = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAction target:self action:@selector(showMenu)];
    self.navigationItem.rightBarButtonItem = systemAction;

    UIBarButtonItem *openItem = [[UIBarButtonItem alloc] initWithTitle:@"Menu" style:UIBarButtonItemStylePlain target:self action:@selector(openButtonPressed)];
    self.navigationItem.leftBarButtonItem = openItem;

    UIImage *back = [UIImage imageNamed:@"back_arrow"];
    UIBarButtonItem *backButton = [[UIBarButtonItem alloc]initWithTitle:@"" style: UIBarButtonItemStylePlain target:self action:@selector(GoBack)];
    [backButton setImage:back];

    UIImage *forward = [UIImage imageNamed:@"forward_arrow"];
    UIBarButtonItem *forwardButton = [[UIBarButtonItem alloc] initWithTitle:@"" style:UIBarButtonItemStyleBordered target:self action:@selector(GoForward)];
    [forwardButton setImage:forward];

    self.navigationItem.leftBarButtonItems = [NSArray arrayWithObjects:openItem, backButton, forwardButton, nil];
}

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奇怪的是，对我有效的方法是将带有图像的按钮的标题设置为一个空格：

barButtonItem.title = @" ";
barButtonItem.image = [UIImage imageNamed:@"MenuIcon.png"];

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“setImage:”记录在哪里？UIBarButtons有一个“setBackgroundImage:forState:barMetrics:”。如果将背景图像设置为“setBackgroundImage:forState:barMetrics:”，则图像将显示在导航栏下方以开始？我在iOS 6上得到了不同的结果，你试过了吗？使用setBackgroundImage:会使图像看起来不正确，并且它们从导航栏下方开始。