How do I supply an initial value to a text field?

In many mobile and web applications, there is often a need for users to input some form of data, be it their name, email address, or password. In Flutter, this can be achieved through the use of a `TextFormField` widget. However, sometimes you might want to pre-populate the text field with an initial value, perhaps to make life easier for the user by providing them with some context or default information.

Using TextFormField and initialValue property

One way to achieve this is by using a `TextFormField` instead of a basic `TextField`. This can be done as follows:

TextFormField(
  initialValue: "I am smart"
)

This will create a text field that displays the string “I am smart” as its initial value. You can replace this with any other string or variable you need to use.

Using TextEditingController and TextField

If you’re already using a `TextField` widget, you can still achieve the desired effect by creating a separate instance of `TextEditingController`. Here’s an example code snippet:

class _FooState extends State {
  TextEditingController _controller;

  @override
  void initState() {
    super.initState();
    _controller = new TextEditingController(text: 'Initial value');
  }

  @override
  Widget build(BuildContext context) {
    return new Column(
      children: [
        new TextField(
          // The TextField is first built, the controller has some initial text,
          // which the TextField shows. As the user edits, the text property of
          // the controller is updated.
          controller: _controller,
        ),
        new RaisedButton(
          onPressed: () {
            // You can also use the controller to manipuate what is shown in the
            // text field. For example, the clear() method removes all the text
            // from the text field.
            _controller.clear();
          },
          child: new Text('CLEAR'),
        ),
      ],
    );
  }
}

In this code snippet, a `_controller` variable is created with an initial value of “Initial value”. This controller is then assigned to a `TextField`, which will display the initial value. The user can edit the text field as usual, and the changes are reflected in the controller’s text property.

Using TextEditingController with TextField

In addition to using the `initialValue` property or creating an instance of `TextEditingController`, you might also need to consider other aspects when working with text fields. For example, how do you update the text field programmatically? How do you remove any existing text from the text field?

Updating the text field programmatically

You can use the controller’s `text` property to set a new value for the text field. Here’s an example:

_controller.text = "New Value";

This will update the text field with the string “New Value”. You can also use other methods, such as `insertText`, `deleteText`, and so on.

Removing existing text from the text field

You can clear any existing text in the text field by calling the controller’s `clear` method:

_controller.clear();

This will remove all characters from the text field, returning it to its initial state.

Conclusion

We have discussed how you can supply an initial value to a text field in Flutter. This can be achieved by using a `TextFormField` with the `initialValue` property or creating an instance of `TextEditingController`. We’ve also explored other aspects of working with text fields, such as updating them programmatically and clearing any existing text.