我們直接在leftBarItem添加一個(gè)自定義button的時(shí)候，這個(gè)button的有效點(diǎn)擊范圍將會(huì)很大，接近navigationBar的titleview。
如果我們只想要響應(yīng)范圍是按鈕的區(qū)域的時(shí)候?？蛇M(jìn)行如下操作：

    +(instancetype)barButtonItemIcon:(NSString *)icon HighlightedIcon:(NSString *)highIcon Target:(id)target action:(SEL)action{

        UIButton *button = [[UIButton alloc] init];
        [button setBackgroundImage:[UIImage imageNamed:icon] forState:UIControlStateNormal];
        [button setBackgroundImage:[UIImage imageNamed:highIcon] forState:UIControlStateHighlighted];
        button.frame = (CGRect){CGPointZero,button.currentBackgroundImage.size};
        [button addTarget:target action:action forControlEvents:UIControlEventTouchUpInside];
        //先將你的按鈕添加到一個(gè)同樣大小的uiview中，然后再將這個(gè)uiview添加到leftBarItem里。
        UIView *view = [[UIView alloc] initWithFrame:button.frame];
        [view addSubview:button];
        return [[UIBarButtonItem alloc]initWithCustomView:view];
    }