flutter - Flutter Datatable-空容器会减慢加载时间

Question

我正在构建一个应用程序，其中将家庭详细信息(分为3个部分)在同一页面上显示为3个不同的数据表。问题是在加载将显示3个数据表的页面之前，捕获了一个异常，此后页面将加载并正确显示3个数据表以及正确的数据。

════════ Exception caught by widgets library ═══════════════════════════════════
The following NoSuchMethodError was thrown building SecondPage(dirty, dependencies: [MediaQuery], state: _SecondPageState#eba94):
The method 'map' was called on null.
Receiver: null
Tried calling: map<DataRow>(Closure: (AdultDetails) => DataRow)

The relevant error-causing widget was
    SecondPage 

具有小部件SecondPage的代码:

 children:<Widget>[
                  Container(
                      height: 50,
                      child: Row(
                        mainAxisSize: MainAxisSize.min,
                        children: <Widget>[
                        Expanded(
                            child: OutlineButton(
                                onPressed: () {
                                  Navigator.push(
                                    context,
                                    MaterialPageRoute(
                                        builder: (context) =>
                                         SecondPage(widget.familyRef)),
                                  );
                                }, 

为了隐藏异常，我将空容器传递给每个数据表。

class SecondPage extends StatefulWidget {
  //final String adultid;
  final String familyRef;

  SecondPage(this.familyRef);
  @override
  _SecondPageState createState() => _SecondPageState();
}
...
Container(
              width: MediaQuery.of(context).size.width,
              child: FittedBox(
                child: DataTable(
                  headingRowHeight: 50,
                  dataRowHeight: 50,
                  //columnSpacing: 10,
                  dividerThickness: 1,
                  columns: [
                    DataColumn(
                      label: Text(
                        "First Name",
                        textAlign: TextAlign.center,
                        overflow: TextOverflow.ellipsis,
                      ),
                      numeric: false,
                      tooltip: "",
                    ),
                    DataColumn(
                      label: Center(
                          child: Text(
                        "Update",
                        textAlign: TextAlign.center,
                        overflow: TextOverflow.ellipsis,
                      )),
                      numeric: false,
                      tooltip: "",
                    ),
                  ],
          rows: list1?.map(
                      (item) => DataRow(cells: [
                        DataCell(
                          Text(item.pensionerName.toString()),
                        ),

                       DataCell(OutlineButton(
                            child: Text("Update"),
                            onPressed: () {
                              Route route = MaterialPageRoute(
                                  builder: (context) => UpdateAdult(
                                      widget.familyRef,
                                      item.adultid,
                                      ));
                              Navigator.push(context, route);
                            },
                          ))
                        ]),
                    )?.toList() ?? [],
              ),

它为我工作-方法'map'在null上调用。错误屏幕没有出现，但是现在每个数据表需要大约3秒钟的时间加载。我该怎么做才能提高加载性能？您的帮助将不胜感激。

Answer 1

使用三元条件
例:

list1 == null ? Container() : list1?.map(
                      (item) => DataRow(cells: [
                        DataCell(
                          Text(item.pensionerName.toString()),
                        ),

                       ...

                    )?.toList() ?? [],
              ),