细微调整NavItem的间距

    UIBarButtonItem * spaceItem = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFixedSpace target:nil action:nil];
    spaceItem.width = -7;

  // 操作按钮
    UIBarButtonItem * backItem = [[UIBarButtonItem alloc] initWithCustomView:backBtn];
    UIBarButtonItem * closeItem = [[UIBarButtonItem alloc] initWithCustomView:closeBtn];
    self.navigationItem.leftBarButtonItems = @[spaceItem,backItem,closeItem];