mutli_image_picker/example/lib/asset_image.dart

import 'dart:typed_data';

import 'package:flutter/material.dart';
import 'package:photo_manager/photo_manager.dart';

class AssetImageWidget extends StatelessWidget {
  final AssetEntity assetEntity;
  final double width;
  final double height;
  final BoxFit boxFit;

  const AssetImageWidget({
    Key key,
    @required this.assetEntity,
    this.width,
    this.height,
    this.boxFit,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    if (assetEntity == null) {
      return _buildContainer();
    }
    return FutureBuilder<Size>(
      builder: (c, s) {
        if (!s.hasData) {
          return Container();
        }
        var size = s.data;
        return FutureBuilder<Uint8List>(
          builder: (BuildContext context, snapshot) {
            if (snapshot.hasData) {
              return _buildContainer(
                child: Image.memory(
                  snapshot.data,
                  width: width,
                  height: height,
                  fit: boxFit,
                ),
              );
            } else {
              return _buildContainer();
            }
          },
          future: assetEntity.thumbDataWithSize(
            size.width.toInt(),
            size.height.toInt(),
          ),
        );
      },
      future: assetEntity.size,
    );
  }

  Widget _buildContainer({Widget child}) {
    child ??= Container();
    return Container(
      width: width,
      height: height,
      child: child,
    );
  }
}