UIToolbar

1.简介
UIToolbar是一种工具条

它内部能直接存放的是UIBarButtonItem
如果想要存放其他控件，比如UIButton，必须先包装成UIBarButtonItem

2.UIBarButtonItem
一般存在于工具条内部

3.通过代码创建UIToolbar

UIToolbar *toolbar = [[UIToolbar alloc] initWithFrame:CGRectMake(0, 0, 320, 44)];
// 设置toolbar的样式
toolbar.barStyle = UIBarStyleBlackTranslucent;

// 左边的item
UIBarButtonItem *left = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:nil action:nil];

// 中间的文字
UIBarButtonItem *center = [[UIBarButtonItem alloc] initWithTitle:@"联系人列表" style:UIBarButtonItemStylePlain target:nil action:nil];

// 右边的item
UIBarButtonItem *right = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemTrash target:nil action:nil];

// 弹簧
UIBarButtonItem *flex = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:nil action:nil];
UIBarButtonItem *flex2 = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:nil action:nil];

// 设置UIToolbar的所有item
toolbar.items = @[left, flex, center,flex2, right];