Handle image uploads in a Flutter Form .

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.

(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)

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