How to detect when a TextField is selected in Flutter?

问题

Stupid Flutter newbie question here...

I have a Flutter TextField which gets covered by the soft keyboard when the field is selected. I need to scroll the field up and out of the way when the keyboard is displayed. This is a pretty common problem and a solution is presented in this StackOverflow post.

I think I have the ScrollController part figured out but how do I detect when the TextField has been selected? There doesn't appear to be any event method (e.g. onFocus(), onSelected(), onTap(), etc).

I tried wrapping the TextField in a GestureDetector but that didn't work either -- apparently the event was never captured.

new GestureDetector(
  child: new TextField(
    decoration: const InputDecoration(labelText: 'City'),
  ),
  onTap: () => print('Text Selected'),
),

This is such a basic requirement that I know there must be an easy solution.

Thanks for the help.

回答1:

I suppose you are looking for FocusNode.

To listen to focus change, you can add a listner to the FocusNode and specify the focusNode to TextField.

Example:

class TextFieldFocus extends StatefulWidget {
  @override
  _TextFieldFocusState createState() => new _TextFieldFocusState();
}

class _TextFieldFocusState extends State<TextFieldFocus> {
  FocusNode _focus = new FocusNode();

  TextEditingController _controller = new TextEditingController();

  @override
  void initState() {
    super.initState();
    _focus.addListener(_onFocusChange);
  }

  void _onFocusChange(){
    debugPrint("Focus: "+_focus.hasFocus.toString());
  }

  @override
  Widget build(BuildContext context) {
    return new Container(
      color: Colors.white,
      child: new TextField(
        focusNode: _focus,
      ),
    );
  }
}

This gist represents how to ensure a focused node to be visible on the ui.

Hope it helps!

回答2:

The easiest and simplest solution is to add the onTap method on TextField.

TextField(
  onTap: () {
    print('Editing stated $widget');
  },
)

回答3:

To be notified about a focus event, you can avoid manually managing widget's state, by using the utility classes FocusScope, Focus.

From the docs (https://api.flutter.dev/flutter/widgets/FocusNode-class.html):

Please see the Focus and FocusScope widgets, which are utility widgets that manage their own FocusNodes and FocusScopeNodes, respectively. If they aren't appropriate, FocusNodes can be managed directly.

Here is a simple example:

FocusScope(
  child: Focus(
    onFocusChange: (focus) => print("focus: $focus"),
    child: TextField(
      decoration: const InputDecoration(labelText: 'City'),
    )
  )
)

回答4:

Simply use onTap function of TextField.

TextField( onTap: () { /Your Code })

来源：https://stackoverflow.com/questions/49341856/how-to-detect-when-a-textfield-is-selected-in-flutter

标签

keyboard

textfield

Flutter