ios UIBarButtonItem rightBarButtonItem Title 设置不了

// rightBarButtonItem Title 设置了不起作用，非要在alloc的时候就设置title才有效

UIBarButtonItem *rightBarItem = [[UIBarButtonItemalloc]initWithTitle:@"退出"style:UIBarButtonItemStyleBorderedtarget:selfaction:@selector(logout)];

    self.navigationItem.rightBarButtonItem = rightBarItem;

//设置颜色，字体大小

    [self.navigationItem.rightBarButtonItemsetTitleTextAttributes:[NSDictionarydictionaryWithObjectsAndKeys:[UIFontboldSystemFontOfSize:14],UITextAttributeFont, [UIColorwhiteColor], UITextAttributeTextColor,nil] forState:UIControlStateNormal];