当我尝试清理流时，在 null 上调用了方法“map”

Question

我有一个流，它提供键入为“客户端”的项目列表。我也有一个搜索栏，用户写一些名字，列表应该过滤搜索结果，当点击其他名为“清除”的按钮时，它应该将列表重置为默认值。所以，我写了这些方法：

//called when tap search button (if it has a text typed)
  void setSearch(String search) {
    _search = search;
    _streamController.add(null);//the error throws here
    load(clean: true);
  }

//called when tap 'clear' button
  void clearSearch() {
    _search = '';
    _offset = 1;
    _clients.clear();
    _streamController.stream.drain();
    _streamController.add(null); //the error throws here
    load(clean: true);
  }

但是当我点击搜索或清除时，它会抛出这个错误：

接收者：空。 NoSuchMethodError：在 null 上调用了方法“map”。尝试调用：map(Closure: (Map) => Client)

我该如何处理？还有另一种清理流的方法吗？如果您需要更多代码，我可以更新问题

更新 这是我的构建方法

Scaffold(
      appBar: appBar(),
      body: Column(
        children: [
          Container(
            padding: EdgeInsets.all(5.0),
            width: MediaQuery.of(context).size.width,
            height: 60.0,
            child: Card(
              elevation: 3,
              child: Container(
                child: TextField(
                  style: TextStyle(
                    color: AppColorSecondary,
                  ),
                  cursorColor: Theme.of(context).primaryColor,
                  textInputAction: TextInputAction.search,
                  decoration: InputDecoration(
                    prefixIcon: Icon(Icons.search, color: AppColorSecondary,),
                    hintStyle: TextStyle(color: AppColorSecondary),
                    filled: true,
                    fillColor: AppColorPrimary,
                    border: OutlineInputBorder(),
                    focusedBorder: OutlineInputBorder(),
                    suffixIcon: GestureDetector(
                      onTap: (){
                        searchController.clear();
                        clientsController.loadMore();
                      },
                      child: FittedBox(
                        alignment: Alignment.center,
                        fit: BoxFit.fitHeight,
                        child: IconTheme(
                          data: IconThemeData(),
                          child: Icon(
                            Icons.clear,
                            color: Colors.black,
                          ),
                        ),
                      ),
                    ),
                  ),
                  controller: searchController,
                  onSubmitted: (value) {
                    clientsController.setSearch(searchController.text);
                  },
                ),
              ),
            ),
          ),
          Expanded(
            child: StreamBuilder(
              stream: clientsController.stream,
              builder: (ctx, snapshot) {
                if (snapshot.error != null) {
                  print(snapshot.error.toString());
                  return Center(
                    child: Text(snapshot.error.toString()),
                  );
                } else if (!snapshot.hasData) {
                  return Center(
                    child: CircularProgressIndicator(),
                  );
                } else if (snapshot.data.length == 0) {
                  return Center(
                    child: Text('0clients'),
                  );
                } else {
                  return RefreshIndicator(
                    onRefresh: clientsController.refresh,
                    child: ListView.builder(
                      controller: scrollController,
                      itemCount: snapshot.data.length + 1,
                      itemBuilder: (ctx, i) {
                        if (i < snapshot.data.length) {
                          return ClientsWidget(snapshot.data[i]);
                        } else if (clientsController.hasMore) {
                          return Padding(
                            padding: EdgeInsets.symmetric(vertical: 32.0),
                            child: Center(child: CircularProgressIndicator()),
                          );
                        } else {
                          return SizedBox(
                            height: 30,
                          );
                        }
                      },
                    ),
                  );
                }
              },
            ),
          )
        ],
      ),
    );
  }

Answer 1

试试_streamController.add([]);