navigationItem文字不显示

//分享按钮
- (void)createRightBtnsAtNavBar{
    self.shareBtn = [UIButton buttonWithType:UIButtonTypeCustom];
    self.shareBtn.frame = CGRectMake(0, 0, 44.0f, 44.0f);
    [self.shareBtn setImage:[UIImage imageNamed:@"share_btn"] forState:UIControlStateNormal];
    [self.shareBtn addTarget:self action:@selector(onShareBtnClicked:) forControlEvents:UIControlEventTouchUpInside];
    UIBarButtonItem *shareItem = [[UIBarButtonItem alloc] initWithCustomView:self.shareBtn];
    
    self.ruleBtn = [UIButton buttonWithType:UIButtonTypeCustom];
    self.ruleBtn.frame = CGRectMake(0, 0, 44, 44);
    [self.ruleBtn setTitle:@"规则" forState:UIControlStateNormal];
    [self.ruleBtn setTintColor:[UIColor redColor]];
    [self.ruleBtn addTarget:self action:@selector(onRuleBtnClicked:) forControlEvents:UIControlEventTouchUpInside];
    UIBarButtonItem *ruleItem = [[UIBarButtonItem alloc] initWithCustomView:self.ruleBtn];
    self.navigationItem.rightBarButtonItems = @[shareItem, ruleItem];
}

这样写的话，规则的按钮能加上去，事件也能响应，但是规则两个字死活显示不出来，所以要改变添加方式如下：

//分享按钮
- (void)createRightBtnsAtNavBar{
    self.shareBtn = [UIButton buttonWithType:UIButtonTypeCustom];
    self.shareBtn.frame = CGRectMake(0, 0, 44.0f, 44.0f);
    [self.shareBtn setImage:[UIImage imageNamed:@"share_btn"] forState:UIControlStateNormal];
    [self.shareBtn addTarget:self action:@selector(onShareBtnClicked:) forControlEvents:UIControlEventTouchUpInside];
    UIBarButtonItem *shareItem = [[UIBarButtonItem alloc] initWithCustomView:self.shareBtn];
    
    UIBarButtonItem *ruleItem = [[UIBarButtonItem alloc] initWithTitle:@"规则" style:UIBarButtonItemStylePlain target:self action:@selector(onRuleBtnClicked:)];
    ruleItem.tintColor = [UIColor blackColor];
    self.navigationItem.rightBarButtonItems = @[shareItem, ruleItem];
}

这样2句代码代替了上边6句代码，而且毫无问题，bingo