修改NavigationBarItem的字体大小和颜色的使用方法

//创建一个左边按钮
UIBarButtonItem *leftButton = [[UIBarButtonItem alloc] initWithTitle:@"<" style:UIBarButtonItemStylePlain target:self action:@selector(clickLeftButton)];
//    leftButton.

[leftButton setTitleTextAttributes:[NSDictionary dictionaryWithObjectsAndKeys:
[UIFont fontWithName:@"Helvetica-Bold" size:17.0], NSFontAttributeName,
[UIColor greenColor], NSForegroundColorAttributeName,
nil]
forState:UIControlStateNormal];
//创建一个右边按钮
UIBarButtonItem *rightButton = [[UIBarButtonItem alloc] initWithTitle:@"登陆" style:UIBarButtonItemStyleDone target:self action:@selector(clickRightButton)];
[rightButton setTitleTextAttributes:[NSDictionary dictionaryWithObjectsAndKeys:
[UIFont fontWithName:@"Helvetica-Bold" size:17.0], NSFontAttributeName,
[UIColor greenColor], NSForegroundColorAttributeName,
nil]
forState:UIControlStateNormal];