有关导航栏的相关认识

1、在导航栏上添加按钮，又两个属性：

navigationItem.rightBarButtonItem和navigationItem.leftBarButtonItem

2、默认情况下，导航栏上的左右按钮只能设置一张图片，要想设置普通和高亮的图片，徐自定义按钮，将按钮传给navigationItem

  具体实现的代码如下事例：

UIButton * leftButton = [UIButton buttonWithType:UIButtonTypeCustom];
    [leftButton setBackgroundImage:[UIImage imageWithNamed:@"navigationbar_friendsearch"] forState:UIControlStateNormal];

    [leftButton setBackgroundImage:[UIImage imageNamed:@"navigationbar_friendsearch_highlighted"] forState:UIControlStateHighlighted];
    leftButton.frame = (CGRect){CGPointZero,leftButton.currentBackgroundImage.size};
    
    [leftButton addTarget:self action:@selector(findFriend) forControlEvents:UIControlEventTouchUpInside];
    self.navigationItem.leftBarButtonItem = [[UIBarButtonItem alloc]initWithCustomView:leftButton];