我正试图在我的flutter应用程序中实现BLoC模式,基本上这个应用程序计算一些结果并将其显示在表格中。我创建了CalculationResultProvider
和CalculationResultBloc
如下
class CalculationResultProvider { List<EstimationResult> resultList = new List(); List<EstimationResult> calculateResult(){ return getInitialData(); } List<EstimationResult> getInitialData(){ var cement = new EstimationResult(); cement.material = "Cement"; cement.unit = "Ton"; cement.qty = 10; var sand = new EstimationResult(); sand.material = "Sand"; sand.unit = "Ton"; sand.qty = 12; var gravel = new EstimationResult(); gravel.material = "Gravel"; gravel.unit = "Ton"; gravel.qty = 5; var steel = new EstimationResult(); steel.material = "Steel"; steel.unit = "Ton"; steel.qty = 5; List<EstimationResult> resultList = new List(); resultList.add(cement); resultList.add(sand); resultList.add(gravel); resultList.add(steel); return resultList; } }
和我的BLoC提供程序类如下
class CalculationResultBloc {
final resultController = StreamController(); // create a StreamController
final CalculationResultProvider provider =
CalculationResultProvider(); // create an instance of our CounterProvider
Stream get getReult =>
resultController.stream; // create a getter for our stream
void updateResult() {
provider
.calculateResult(); // call the method to increase our count in the provider
resultController.sink.add(provider.resultList); // add the count to our sink
}
void dispose() {
resultController.close(); // close our StreamController
}
}
然后我需要在表格小部件中显示这些数据
class ResultTableWidget extends StatefulWidget {
@override
State<StatefulWidget> createState() => ResultTableWidgetState();
}
class ResultTableWidgetState extends State {
final bloc =
CalculationResultBloc(); // create an instance of the counter bloc
@override
Widget build(BuildContext context) {
return StreamBuilder(
stream: bloc.getReult,
initialData: CalculationResultProvider().getInitialData(),
builder: (context, snapshot) {
DataTable(
columns: [
DataColumn(label: Text('Patch')),
DataColumn(label: Text('Version')),
DataColumn(label: Text('Ready')),
],
rows:
'${snapshot.data}' // Loops through dataColumnText, each iteration assigning the value to element
.map(
((element) => DataRow(
cells: <DataCell>[
DataCell(Text(element[
"Name"])), //Extracting from Map element the value
DataCell(Text(element["Number"])),
DataCell(Text(element["State"])),
],
)),
)
.toList(),
);
});
}
@override
void dispose() {
bloc.dispose();
super.dispose();
}
}
要迭代返回表,它应该是List<EstimationResult>
但如何将快照转换为List<EstimationResult>
?
在bloc类或widget类中转换的最佳位置在哪里?
我很新的飞镖和扑,任何人都可以回答我的问题吗?
谢谢。
你的小部件类将不知道你的StreamBuilder
中的流函数给出的数据类型的线索,有很多方法可以在流式传输之前在BloC
中转换数据,但是所有这些方法都没用,因为对于小部件类它只是一个snapshot
,您在编译时可以访问的唯一字段是应用于data
字段等通用快照的字段。因此,访问自定义列表字段的唯一方法是为StreamBuilder
提供其stream
函数所需的数据类型:
StreamBuilder<List<EstimationResult>>(
stream: bloc.getReult,
initialData: CalculationResultProvider().getInitialData(),
builder: (context, snapshot) {
//...
}
);
通过这种方式,您可以将snapshot
视为List<EstimationResult>
,并在收到实际快照之前访问内部字段和函数。在您的情况下,您可能应该将EstimationResult
类导入到您的widget类中。