怎樣定製navgation上的按鈕，設置本身的風格的UIBarButtonItem

在使用 UIBarButtonItem  系統提供的幾個函數的時發現添加背景圖片後會有個小框，並且很難去掉，影響效果，並且UIBarButtonItem好像不能使用frame  的屬性，因此能夠下面方法定製本身的UIBarButtonItem

 UIImage* p_w_picpath= [UIImage p_w_picpathNamed:@"綁定彈出－返回.png"];
        CGRect frame_1= CGRectMake(0, 0, p_w_picpath.size.width, p_w_picpath.size.height-4);
        UIButton* backButton= [[UIButton alloc] initWithFrame:frame_1];
        [backButton setBackgroundImage:p_w_picpath 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];

//定製本身的風格的 UIBarButtonItem
 UIBarButtonItem* someBarButtonItem= [[UIBarButtonItem alloc] initWithCustomView:backButton];
        [self.navigationItem setLeftBarButtonItem:someBarButtonItem];
        [someBarButtonItem release];
        [backButton release];