DropDownButton

DropdownButton<T> class
A Material Design button for selecting from a list of items.

A dropdown button lets the user select from a number of items. The
button shows the currently selected item as well as an arrow that
opens a menu for selecting another item.

Material로 design된 button이라고 한다. list에서 item을 선택하는거라고 한다. dropdown button은 사용자가 list의 item을 선택할 수 있게 해준다. button은 현재 선택된 item을 보여주고, 뿐만아니라 화살표도 보여준다고 한다. 화살표는 menu를 열어서 다른 item을 선택할 수 있게 해준다고 한다.

Updating to DropdownMenu There is a Material 3 version of this component, DropdownMenu that is preferred for applications that are configured for Material 3 (see ThemeData.useMaterial3). The DropdownMenu widget’s visuals are a little bit different, see the Material 3 spec at m3.material.io/components/menus/guidelines for more details.

The DropdownMenu widget’s API is also slightly different. To update from DropdownButton to DropdownMenu, you will need to make the following changes:

Instead of using DropdownButton.items, which takes a list of DropdownMenuItems, use DropdownMenu.dropdownMenuEntries, which takes a list of DropdownMenuEntry’s.

Instead of using DropdownButton.onChanged, use DropdownMenu.onSelected, which is also a callback that is called when the user selects an entry.

In DropdownMenu it is not required to track the current selection in your app’s state. So, instead of tracking the current selection in the DropdownButton.value property, you can set the DropdownMenu.initialSelection property to the item that should be selected before there is any user action.

You may also need to make changes to the styling of the DropdownMenu, see the properties in the DropdownMenu constructor for more details.

See the sample below for an example of migrating from DropdownButton to DropdownMenu.