UIToolBar

    //UIToolBar  是导航控制器默认隐藏的工具条
    //设置UIToolBar的隐藏状态
    self.navigationController.toolbarHidden = NO;

    //如何找到UIToolBar   self.navigationController.toolbar
    //UIToolBar高度：44

    //设置UIToolBar类型:barStyle
    self.navigationController.toolbar.barStyle = UIBarStyleDefault;
    //设置UIToolBar的颜色:barTintColor
    self.navigationController.toolbar.barTintColor = [UIColor redColor];
    //设置UIToolBar的图片
    [self.navigationController.toolbar setBackgroundImage:[UIImage imageNamed:@"toolBar.png"] forToolbarPosition:UIToolbarPositionBottom barMetrics:UIBarMetricsDefault];

    //UIBarButtonItem  文字类型
    UIBarButtonItem *wordButton = [[UIBarButtonItem alloc] initWithTitle:@"button" style:UIBarButtonItemStylePlain target:self action:@selector(barButtonClick:)];

    //UIBarButtonItem  图片类型
    UIBarButtonItem *imageButton = [[UIBarButtonItem alloc] initWithImage:[UIImage imageNamed:@"itemImage.png"] style:UIBarButtonItemStylePlain target:self action:@selector(imageButtonClick:)];

    //UIBarButtonItem  系统类型
    UIBarButtonItem *systemButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemBookmarks target:self action:@selector(systemButtonClick:)];

    //创建空格
    //会均分掉空白部分，空格的点击事件不会实现，无效
    UIBarButtonItem *space = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:self action:@selector(spaceClick:)];

    //向UIToolBar上面添加按钮   self.toolbarItems
    //需要接收数组：数组里面的元素必须是UIBarButtonItem类型
    self.toolbarItems = @[space, wordButton, space, imageButton, space, systemButton, space];