flutter_preloading_image_builder.dart

import 'package:flutter/widgets.dart';

class PreloadingImageBuilder extends StatefulWidget {
  final ImageProvider imageProvider;
  final AsyncWidgetBuilder<dynamic> builder;

  PreloadingImageBuilder({this.imageProvider, this.builder});

  @override
  _PreloadingImageBuilderState createState() => _PreloadingImageBuilderState();
}

class _PreloadingImageBuilderState extends State<PreloadingImageBuilder> {
  Future future;

  @override
  void didChangeDependencies() {
    super.didChangeDependencies();

    if (this.future == null) {
      this.future = precacheImage(this.widget.imageProvider, context).then((value) => true);
    }
  }

  @override
  Widget build(BuildContext context) {
    return FutureBuilder(
      future: this.future,
      builder: this.widget.builder,
    );
  }
}