mutli_image_picker/example/lib/main.dart

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

void main() => runApp(new MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Pick Image Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(title: 'Pick Image Demo'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> with LoadingDelegate {
  String currentSelected = "";

  void _pickImage() async {
    List<AssetEntity> imgList = await PhotoPicker.pickAsset(
      // BuildContext required
      context: context,

      /// The following are optional parameters.
      themeColor: Colors.green,
      // the title color and bottom color
      padding: 1.0,
      // item padding
      dividerColor: Colors.grey,
      // divider color
      disableColor: Colors.grey.shade300,
      // the check box disable color
      itemRadio: 0.88,
      // the content item radio
      maxSelected: 8,
      // max picker image count
      provider: I18nProvider.english,
      // provider: I18nProvider.chinese,
      // i18n provider ,default is chinese. , you can custom I18nProvider or use ENProvider()
      rowCount: 3,
      // item row count
      textColor: Colors.white,
      // text color
      thumbSize: 150,
      // preview thumb size , default is 64
      sortDelegate: SortDelegate.common,
      // default is common ,or you make custom delegate to sort your gallery
      checkBoxBuilderDelegate: DefaultCheckBoxBuilderDelegate(
        activeColor: Colors.white,
        unselectedColor: Colors.white,
      ),
      // default is DefaultCheckBoxBuilderDelegate ,or you make custom delegate to create checkbox

      loadingDelegate: this,
      // if you want to build custom loading widget,extends LoadingDelegate, [see example/lib/main.dart]

      badgeDelegate: const DurationBadgeDelegate(),
    );

    if (imgList == null) {
      currentSelected = "not select item";
    } else {
      List<String> r = [];
      for (var e in imgList) {
        var file = await e.file;
        r.add(file.absolute.path);
      }
      currentSelected = r.join("\n\n");
    }
    setState(() {});
  }

  @override
  Widget buildBigImageLoading(
      BuildContext context, AssetEntity entity, Color themeColor) {
    return Center(
      child: Container(
        width: 50.0,
        height: 50.0,
        child: CupertinoActivityIndicator(
          radius: 25.0,
        ),
      ),
    );
  }

  @override
  Widget buildPreviewLoading(
      BuildContext context, AssetEntity entity, Color themeColor) {
    return Center(
      child: Container(
        width: 50.0,
        height: 50.0,
        child: CupertinoActivityIndicator(
          radius: 25.0,
        ),
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text(widget.title),
      ),
      body: Container(
        child: Center(
          child: Text(
            '$currentSelected',
            textAlign: TextAlign.center,
          ),
        ),
      ),
      floatingActionButton: new FloatingActionButton(
        onPressed: _pickImage,
        tooltip: 'pickImage',
        child: new Icon(Icons.add),
      ),
    );
  }
}