Flutter之下拉刷新，上拉加载更多

Flutter之下拉刷新，上拉加载更多

// 下拉刷新，上拉加载更多
class PullAndLoadViewDemo extends StatefulWidget {
  @override
  State createState() => _PullAndLoadViewDemo();
}

class _PullAndLoadViewDemo extends State {
  List sourceData = [];

  // 当前页数
  int _currentPage = 1;

  // 总页数
  int _totalPage = 3;

  // 每页数据条数
  int _pageCount = 20;

  // 是否加载中
  bool isLoading = false;

  // 滑动控制器
  ScrollController _scrollController = ScrollController();

  @override
  void initState() {
    super.initState();
    _scrollController.addListener(() {
      // 实现预加载
      double edge = 50.0;
      if (_scrollController.position.maxScrollExtent -
              _scrollController.position.pixels <=
          edge) {
        // 加载更多
        _loadMore();
      }
    });
    _refreshData();
  }

  @override
  void dispose() {
    super.dispose();
    _scrollController.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("列表刷新案例"),
      ),
      body: RefreshIndicator(
          child: ListView.builder(
            itemBuilder: (context, index) {
              return _generateListItemView(index);
            },
            itemCount: _getItemCount(),
            controller: _scrollController,
            // 保持任何情况下都能滚动
            physics: const AlwaysScrollableScrollPhysics(),
          ),
          onRefresh: _refreshData),
    );
  }

  // 下拉刷新数据
  Future _refreshData() async {
    await Future.delayed(Duration(seconds: 2), () {
      setState(() {
        _currentPage = 1;
        sourceData.clear();
        sourceData.addAll(List.generate(_pageCount, (index) => "我是刷新后据$index"));
      });
    });
  }

  // 上拉加载更多数据
  Future _loadMore() async {
    if (!isLoading) {
      setState(() {
        isLoading = true;
      });
      await Future.delayed(Duration(seconds: 2), () {
        setState(() {
          _currentPage++;
          if (_currentPage < _totalPage) {
            sourceData.addAll(List.generate(
                _pageCount, (index) => "加载更多：页数$_currentPage,条数$index"));
          } else if (_currentPage == _totalPage) {
            //TODO 模拟最后一页数据
            sourceData.addAll(List.generate(
                _pageCount - 5, (index) => "加载更多：页数$_currentPage,条数$index"));
          }
          isLoading = false;
        });
      });
    }
  }

  int _getItemCount() {
    if (sourceData.length == 0) {
      return 0;
    }
    return sourceData.length + 1;
  }

  Widget _generateListItemView(index) {
    if (_currentPage >= _totalPage && index == sourceData.length) {
      return _loadMoreFinishedWidget();
    }
    if (index < sourceData.length) {
      return ListTile(
        title: Text(sourceData[index]),
      );
    }
    return _loadMoreDateWidget();
  }
  // 加载完成
  Widget _loadMoreFinishedWidget() {
    return Center(
      child: Padding(
        padding: EdgeInsets.all(10.0),
        child: Text(
          "没有更多数据了",
          style: TextStyle(fontSize: 16.0),
        ),
      ),
    );
  }

  // 加载中...
  Widget _loadMoreDateWidget() {
    return Center(
      child: Padding(
        padding: EdgeInsets.all(10.0),
        child: Row(
          mainAxisAlignment: MainAxisAlignment.center,
          crossAxisAlignment: CrossAxisAlignment.center,
          children: [
            SizedBox(
              width: 30.0,
              height: 30.0,
              child: CircularProgressIndicator(
                strokeWidth: 1.0,
              ),
            ),
            Padding(padding: EdgeInsets.all(10.0)),
            Text(
              "加载中....",
              style: TextStyle(fontSize: 16.0),
            ),
          ],
        ),
      ),
    );
  }
}