从API提取数据时如何显示进度指示器？

如何解决从API提取数据时如何显示进度指示器？

问题很简单，但是我找不到合适的解决方案。我有一个搜索屏幕，这是我想要做的。

• 首次启动屏幕时，我想在Text小部件中显示一条消息，“您的结果将出现在这里”。
• 如果用户在搜索框中输入内容，然后按搜索，我想显示CircularProgressIndicator。
• 然后，当收到API响应时，我想显示ListView或Text说“什么都没找到”。
• 如果用户再次搜索某些内容，我想再次显示CircularProgressIndicator。

如何使用Stream实现此行为？以下是我到目前为止的代码：

小部件

StreamBuilder<List<Model>>(
  stream: bloc.searchStream,builder: (context,snapshot) {

    if (snapshot.hasError) {
      return Center(
        child: Text(
          'Error occurred'
        ),);
    }

    if (!snapshot.hasData) {
      return Center(
        child: Text(
          'Your results will appear here'
        ),);
    }

    if (snapshot.hasData && snapshot.data.length < 1) {
      return Center(
        child: Text(
          'Found nothing'
        ),);
    }

    // Where should I put my CircularProgressIndicator?

    return ListView.separated(
      itemCount: snapshot.data.length,separatorBuilder: (context,index) => Divider(height: 1),itemBuilder: (context,index) {
        final item = snapshot.data[index];
        return ItemWidget(item);
      },);
  },)

BLoC

final _searchStreamController = StreamController<List<Model>>();
Stream<List<Model>> get searchStream => _searchStreamController.stream;

void search(String searchTerm) async {

  if (searchTerm.isEmpty) {
    _searchStreamController.add(null);
    return;
  }

  final client = HttpClient();
  client.method = HttpMethod.POST;
  client.endPoint = 'search';
  client.addData('query',searchTerm);

  try {
    final responseStr = await client.execute();
    final response = SearchResponse.fromJson(responseStr);
    _searchStreamController.add(response.data);
  } catch (e) {
    _searchStreamController.addError(e);
  }
}

我想每次调用CircularProgressIndicator函数时显示search(String searchedTerm)。

谢谢。

解决方法

    StreamBuilder<List<Model>>(
      stream: bloc.searchStream,builder: (context,snapshot) {
 
        if (snapshot.hasData) {
         if (snapshot.data.length ==0){ 
              return  Center(
                 child: Text(
                      'Found nothing'
                    ),);
    
            } 
        return ListView.separated(
          itemCount: snapshot.data.length,separatorBuilder: (context,index) => Divider(height: 1),itemBuilder: (context,index) {
            final item = snapshot.data[index];
            return ItemWidget(item);
          },);
        }else if (snapshot.hasError) {
          return Center(
            child: Text(
              'Error occurred'
            ),);
      }else {
         return Center(
            child:CircularProgressIndicator()
          );
       }
      },)

给出一个初始Text（）小部件，其值为“结果将在此处显示”， 然后在Button的onClick上，将原始的Text（）小部件替换为StreamBuilder

,

您可以尝试：

StreamBuilder<List<Model>>(
          builder: (context,snapshot) {
            switch (snapshot.connectionState) {
              case ConnectionState.none:
                return Center(child: Text('Your results will appear here'));

              case ConnectionState.active:
              case ConnectionState.waiting:
                return Center(child: CircularProgressIndicator());

              case ConnectionState.done:
                if (snapshot.hasError)
                  return Center(child: Text('Error occurred'));

                if (snapshot.data.isEmpty) {
                  return Container(child: Center(child: Text('Found nothing')));
                } else {
                  return ListView.separated(
                    itemCount: snapshot.data.length,index) {
                      final item = snapshot.data[index];
                      return ItemWidget(item);
                    },);
                }
            }
            return Center(child: Text('Your results will appear here'));
          },)

,

这是我必须达到的骇客。如果有更好的方法可以解决此问题，请发布答案，我将其标记为正确。

黑客

class JugarModel<T> {
  bool isProcessing;
  T data;

  JugarModel({this.isProcessing,this.data});
}

然后使用此isProcessing属性检查是否显示CircularProgressIndicator或ListView。其余代码变为：

小工具

StreamBuilder<JugarModel>(
  stream: bloc.searchStream,snapshot) {

    if (snapshot.hasError) {
      return Center(
        child: Text(
          'Error occurred'
        ),);
    }

    if (!snapshot.hasData) {
      return Center(
        child: Text(
          'Your results will appear here'
        ),);
    }

    if (snapshot.hasData && snapshot.data.data.isEmpty) {

      if (snapshot.data.isProcessing) {
        return Center(
          child: CircularProgressIndicator(),);
      } else {
        return Center(
          child: Text(
            'Found nothing'
          ),);
      }
    }

    return ListView.separated(
      itemCount: snapshot.data.data.length,index) {
        final item = snapshot.data.data[index];
        return ItemWidget(item);
      },);
  },)

BLoC

final _searchStreamController = StreamController<JugarModel<List<Data>>>();
Stream<JugarModel<List<Data>>> get searchStream => _searchStreamController.stream;

void search(String searchTerm) async {

  if (searchTerm.isEmpty) {
    _searchStreamController.add(null);
    return;
  }

  final client = HttpClient();
  client.method = HttpMethod.POST;
  client.endPoint = 'search';
  client.addData('query',searchTerm);

  // This MAGIC line will call StreamBuilder callback with isProcessing set to true.
  _searchStreamController.add(JugarModel<List<Data>>(isProcessing: true,data: List()));
  try {
    final responseStr = await client.execute();
    final response = SearchResponse.fromJson(responseStr);

    // And after we've received response from API and parsed it,we're calling StreamBuilder
    // callback again with isProcessing set to false.
    _searchStreamController.add(JugarModel<List<Data>>(isProcessing: false,data: response.data));
  } catch (e) {
    _searchStreamController.addError(e);
  }
}