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>)

name	type	required	description
previewImageBuilder	Widget Function(BuildContext, T)	*	How the image is rendered below the upload button
buttonBuilder	Widget Function(BuildContext, [int])	*	The display of the button. Do not use FlatButton; the button is already wrapped in a GestureRecognizer
initializeFileAsImage	T Function(File)	*	Convert an upload to the adapter class
controller	ImageFieldController		Direct access to the images currently displayed or uploaded
initialValue	List		Images 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.
onSaved	VoidCallback Function(List)		Handle the uploaded/remote images when the form is saved
validator	VoidCallback Function(List)		Handle the uploaded/remote images when the form is validated
errorTextStyle	TextStyle		Control how text display when field is invalid; often it's best to use Theme.of(context).inputDecorationTheme.errorStyle
autoValidate	bool		If field should autovalidate (defaults to false)
shouldAllowMultiple	bool		If field permits more than one image upload (defaults to true)

Thanks

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