ImageFormField

Handle image uploads in a Flutter Form.

Usage

In order to fully customize the photo upload field, several callbacks and classes are required. In most cases, you will be mixing photos from a remote source and a local upload. For these, an adapter layer is useful:

class ImageInputAdapter {
  /// Initialize from either a URL or a file, but not both.
  ImageInputAdapter({
    this.file,
    this.url
  }) : assert(file != null || url != null), assert(file != null && url == null), assert(file == null && url != null);

  /// An image file
  final File file;
  /// A direct link to the remote image
  final String url;

  /// Render the image from a file or from a remote source.
  Widget widgetize() {
    if (file != null) {
      return Image.file(file);
    } else {
      return FadeInImage(
        image: NetworkImage(url),
        placeholder: AssetImage("assets/images/placeholder.png"),
        fit: BoxFit.contain,
      );
    }
  }
}

Finally, in a Flutter Form:

import 'package:image_form_field/image_form_field.dart';

ImageFormField<ImageInputAdapter>(
  previewImageBuilder: (_, ImageInputAdapter image) =>
    image.widgetize(),
  buttonBuilder: (_, int count) =>
    Container(
      child: Text(
        count == null || count < 1 ? "Upload Image" : "Upload More"
      )
    )
  initializeFileAsImage: (File file) =>
    ImageInputAdapter(file: file),
  initialValue: existingPhotoUrl == null ? null : (List<ImageInputImageAdapter>()..add(ImageInputImageAdapter(url: existingPhotoUrl))),
  // Even if `shouldAllowMultiple` is true, images will always be a `List` of the declared type (i.e. `ImageInputAdater`).
  onSaved: (images) _images = images,
)

For a full example that includes uploading an image, see example/lib/main.dart.

Parameters

(T == declared display type, i.e. ImageFormField<T>)

nametyperequireddescription
previewImageBuilderWidget Function(BuildContext, T)*How the image is rendered below the upload button
buttonBuilderWidget Function(BuildContext, int)*The display of the button. Do not use FlatButton; the button is already wrapped in a GestureRecognizer
initializeFileAsImageT Function(File)*Convert an upload to the adapter class
controllerImageFieldControllerDirect access to the images currently displayed or uploaded
initialValueListImages displayed on initial render; if initialValue is set in initState or by some other non-pass through method, do not render the field until the value is set.
onSavedVoidCallback Function(List)Handle the uploaded/remote images when the form is saved
validatorVoidCallback Function(List)Handle the uploaded/remote images when the form is validated
errorTextStyleTextStyleControl how text display when field is invalid; often it's best to use Theme.of(context).inputDecorationTheme.errorStyle
autoValidateboolIf field should autovalidate (defaults to false)
shouldAllowMultipleboolIf field permits more than one image upload (defaults to true)

Thanks

Props to AllGo for providing the initial support for this project.

Libraries

image_form_field