Trying to make an ImageFormField

form.dart

class ImageFormState extends FormFieldState<File> {
  File _image;

  Future getImage() async {
    var image = await ImagePicker.pickImage(source: ImageSource.camera);
    this._image= image;
  }

  @override
  Widget build(BuildContext context) {
    return _image == null
        ? new RaisedButton(
          onPressed: () {
            getImage();
          },
          child: Text('Select Image'),
        ):
        new Image.file(_image);

  }
}

class ImageFormField extends FormField<File> {

  @override
  FormFieldState<File> createState() => ImageFormState();
}