怎样定制navgation上的按钮，设置自己的风格的UIBarButtonItem

在使用 UIBarButtonItem  系统提供的几个函数的时发现添加背景图片后会有个小框，而且很难去掉，影响效果，而且UIBarButtonItem好像不能使用frame  的属性，所以可以下面方法定制自己的UIBarButtonItem

 UIImage* image= [UIImage imageNamed:@"绑定弹出－返回.png"];
        CGRect frame_1= CGRectMake(0, 0, image.size.width, image.size.height-4);
        UIButton* backButton= [[UIButton alloc] initWithFrame:frame_1];
        [backButton setBackgroundImage:image forState:UIControlStateNormal];
        [backButton setTitle:@"返回" forState:UIControlStateNormal];
        [backButton setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];
        backButton.titleLabel.font=[UIFont systemFontOfSize:16];
        [backButton addTarget:self action:@selector(doBack:) forControlEvents:UIControlEventTouchUpInside];

//定制自己的风格的 UIBarButtonItem
 UIBarButtonItem* someBarButtonItem= [[UIBarButtonItem alloc] initWithCustomView:backButton];
        [self.navigationItem setLeftBarButtonItem:someBarButtonItem];
        [someBarButtonItem release];
        [backButton release];