lift-app/lib/widgets/my_refresh_list.dart

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

import 'package:liftmanager/res/resources.dart';
import 'package:liftmanager/utils/theme_utils.dart';
import 'package:liftmanager/widgets/state_layout.dart';

/// 封装下拉刷新与加载更多
class MyListView extends StatefulWidget {

  const MyListView({
    Key key,
    @required this.itemCount,
    @required this.itemBuilder,
    @required this.onRefresh,
    this.loadMore,
    this.hasMore : false,
    this.stateType : StateType.empty,
    this.pageSize : 10,
    this.padding,
    this.itemExtent,
  }): super(key: key);

  final RefreshCallback onRefresh;
  final LoadMoreCallback loadMore;
  final int itemCount;
  final bool hasMore;
  final IndexedWidgetBuilder itemBuilder;
  final StateType stateType;
  /// 一页的数量，默认为10
  final int pageSize;
  final EdgeInsetsGeometry padding;
  final double itemExtent;

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

typedef RefreshCallback = Future<void> Function();
typedef LoadMoreCallback = Future<void> Function();

class _MyListViewState extends State<MyListView> {

  /// 是否正在加载数据
  bool _isLoading = false;

  @override
  Widget build(BuildContext context) {
    return SafeArea(
      child: NotificationListener(
        onNotification: (ScrollNotification note){
          /// 确保是垂直方向滚动，且滑动至底部
          if (note.metrics.pixels == note.metrics.maxScrollExtent && note.metrics.axis == Axis.vertical){
            _loadMore();
          }
          return true;
        },
        child: RefreshIndicator(
            onRefresh: widget.onRefresh,
            child: widget.itemCount == 0 ? StateLayout(type: widget.stateType) : ListView.builder(
                shrinkWrap: true,
                itemCount: widget.loadMore == null ? widget.itemCount : widget.itemCount + 1,
                padding: widget.padding,
                itemExtent: widget.itemExtent,
                itemBuilder: (BuildContext context, int index){
                  /// 不需要加载更多则不需要添加FootView
                  if (widget.loadMore == null){
                    return widget.itemBuilder(context, index);
                  }else{
                    return index < widget.itemCount ? widget.itemBuilder(context, index) : MoreWidget(widget.itemCount, widget.hasMore, widget.pageSize);
                  }
                }
            )
        ),
      ),
    );
  }

  Future _loadMore() async {
    if (widget.loadMore == null){
      return;
    }
    if (_isLoading) {
      return;
    }
    if (!widget.hasMore){
      return;
    }
    _isLoading = true;
    await widget.loadMore();
    _isLoading = false;
  }

}

class MoreWidget extends StatelessWidget {

  const MoreWidget(this.itemCount, this.hasMore, this.pageSize);

  final int itemCount;
  final bool hasMore;
  final int pageSize;

  @override
  Widget build(BuildContext context) {
    final style =  const TextStyle(color: Color(0x8A000000));
    return Padding(
      padding: const EdgeInsets.symmetric(vertical: 10.0),
      child: Row(
        mainAxisAlignment: MainAxisAlignment.center,
        crossAxisAlignment: CrossAxisAlignment.center,
        children: <Widget>[
          hasMore ? const CupertinoActivityIndicator() : Gaps.empty,
          hasMore ? Gaps.hGap5 : Gaps.empty,
          /// 只有一页的时候，就不显示FooterView了
          Text(hasMore ? '正在加载中...' : (itemCount < pageSize ? '' : '没有了呦~'), style: style),
        ],
      ),
    );
  }
}