Action<T extends Intent> class abstract

Base class for an action or command to be performed.

Actions are typically invoked as a result of a user action. For example, the Shortcuts widget will map a keyboard shortcut into an Intent, which is given to an ActionDispatcher to map the Intent to an Action and invoke it.

The ActionDispatcher can invoke an Action on the primary focus, or without regard for focus.

Action Overriding

When using a leaf widget to build a more specialized widget, it's sometimes desirable to change the default handling of an Intent defined in the leaf widget. For instance, TextField's SelectAllTextIntent by default selects the text it currently contains, but in a US phone number widget that consists of 3 different TextFields (area code, prefix and line number), SelectAllTextIntent should instead select the text within all 3 TextFields.

An overridable Action is a special kind of Action created using the Action.overridable constructor. It has access to a default Action, and a nullable override Action. It has the same behavior as its override if that exists, and mirrors the behavior of its defaultAction otherwise.

The Action.overridable constructor creates overridable Actions that use a BuildContext to find a suitable override in its ancestor Actions widget. This can be used to provide a default implementation when creating a general purpose leaf widget, and later override it when building a more specialized widget using that leaf widget. Using the TextField example above, the TextField widget uses an overridable Action to provide a sensible default for SelectAllTextIntent, while still allowing app developers to change that if they add an ancestor Actions widget that maps SelectAllTextIntent to a different Action.

See the article on Using Actions and Shortcuts for a detailed explanation.

See also:

• Shortcuts, which is a widget that contains a key map, in which it looks up key combinations in order to invoke actions.
• Actions, which is a widget that defines a map of Intent to Action and allows redefining of actions for its descendants.
• ActionDispatcher, a class that takes an Action and invokes it, passing a given Intent.
• Action.overridable for an example on how to make an Action overridable.