Class KeyboardManager

All Implemented Interfaces:
KeyboardChannel.KeyboardMethodHandler, InputConnectionAdaptor.KeyboardDelegate

Processes keyboard events and cooperate with TextInputPlugin.

Flutter uses asynchronous event handling to avoid blocking the UI thread, but Android requires that events are handled synchronously. So when the Android system sends new @{link KeyEvent} to Flutter, Flutter responds synchronously that the key has been handled so that it won't propagate to other components. It then uses "delayed event synthesis", where it sends the event to the framework, and if the framework responds that it has not handled the event, then this class synthesizes a new event to send to Android, without handling it this time.

Flutter processes an Android KeyEvent with several components, each can choose whether to handled the event, and only unhandled events can move to the next section.

  • Keyboard: Dispatch to the KeyboardManager.Responders simultaneously. After all responders have responded (asynchronously), the event is considered handled if any responders decide to handle.
  • Text input: Events are sent to TextInputPlugin, processed synchronously with a result of whether it is handled.
  • "Redispatch": If there's no currently focused text field in TextInputPlugin, or the text field does not handle the KeyEvent either, the KeyEvent will be sent back to the top of the activity's view hierachy, allowing it to be "redispatched". The KeyboardManager will remember this event and skip the identical event at the next encounter.