Flutter | 超实用简单菜单弹出框 PopupMenuButton

相信在实际开发过程当中，肯定少不了这样的功能：

点击 AppBar 右上角的按钮，弹出一个菜单供用户选择。

幸运的是，Flutter 提供给我们了一个 Widget，直接就能实现如上的效果。

PopupMenuButton

还是老规矩，先看官方的说明：

Displays a menu when pressed and calls onSelected^[1] when the menu is dismissed because an item was selected. The value passed to onSelected^[2] is the value of the selected menu item.

One of child^[3] or icon^[4] may be provided, but not both. If icon^[5] is provided, then PopupMenuButton^[6] behaves like an IconButton^[7].

If both are null, then a standard overflow icon is created (depending on the platform).

大致意思为：