Flutter:Future 函数正在连续调用

Question

我使用 future 函数从 API 检索数据，并使用 Consumer 来包装它，因为只有当数据发生更改时，我的列表才会更新。我的代码工作正常，但我 future 的函数正在不断调用。我的代码如下

                    Consumer<Category>(
                      builder: (context, category, child) {
                        return FutureBuilder(
                            future: category.getAllCategories(), //returns a list
                            builder: (BuildContext context, AsyncSnapshot snapshot) {
                              if (!snapshot.hasData || snapshot.data.isEmpty) {
                                return Center(
                                  child: Container(
                                    child: CircularProgressIndicator(),
                                  ),
                                );
                              } else {
                                return ListView.builder(
                                    scrollDirection: Axis.horizontal,
                                    itemCount:
                                        category.getlength != 0 || category.getlength != null || !category.getAllCatisempty ? category.getlength : 0,
                                    shrinkWrap: true,
                                    itemBuilder: (context, index) {
                                      return InkWell(
                                        onTap: () async {
                                          try {

                                            print('connection Status ${await DataConnectionChecker().connectionStatus}');
                                            setState(() {

                                              _selectedIndex = index;
                                              timeCount = 0;

                                            });

                                            productsProvider.clearProductList();
                                            productsProvider.getAllProductsInCategory(category.allCategoryList[index].catId);

                                            setState(() {
                                              catId = category.allCategoryList[index].catId;
                                            });
                                          } catch (e) {
                                            print('exception category click $e');
                                          }
                                        },
                                        child: Column(
                                          crossAxisAlignment: CrossAxisAlignment.center,
                                          children: <Widget>[
                                            Card(
                                              color: _selectedIndex != null && _selectedIndex == index ? selectedColor : defColor,
                                              elevation: _selectedIndex != null && _selectedIndex == index ? 4.0 : 1.0,
                                              child: Center(
                                                child: Padding(
                                                  padding: const EdgeInsets.all(3.0),
                                                  child: Container(
                                                    child: Padding(
                                                      padding: const EdgeInsets.all(4.0),
                                                      child: Column(
                                                        children: <Widget>[
                                                          Image.network(
                                                            category.allCategoryList[index].catThumbnail,
                                                            width: 80.0,
                                                            height: 50.0,
                                                            scale: 1.0,
                                                            loadingBuilder: (BuildContext context, Widget child, ImageChunkEvent loadingProgress) {
                                                              if (loadingProgress == null) return child;
                                                              return Center(
                                                                child: CircularProgressIndicator(
                                                                  value: loadingProgress.expectedTotalBytes != null
                                                                      ? loadingProgress.cumulativeBytesLoaded / loadingProgress.expectedTotalBytes
                                                                      : null,
                                                                ),
                                                              );
                                                            },
                                                          ),
                                                          Padding(
                                                            padding: const EdgeInsets.only(top: 4.0),
                                                            child: Text(
                                                              category.allCategoryList[index].catName,
                                                              textAlign: TextAlign.center,
                                                              style: TextStyle(color: Colors.black, fontSize: 10.0, fontWeight: FontWeight.w500),
                                                            ),
                                                          )
                                                        ],
                                                      ),
                                                    ),
                                                  ),
                                                ),
                                              ),
                                            ),
                                          ],
                                        ),
                                      );
                                    });
                              }
                            });
                      },
                    )

这是我的日志

I/flutter (25780): getAllCategories 
I/flutter (25780): getAllCategories 
I/flutter (25780): getAllCategories 
I/flutter (25780): getAllCategories 
I/flutter (25780): getAllCategories 
I/flutter (25780): getAllCategories 
I/flutter (25780): getAllCategories 
I/flutter (25780): getAllCategories 
I/flutter (25780): getAllCategories 
I/flutter (25780): getAllCategories 
I/flutter (25780): getAllCategories 

这种情况持续不断。

谁能帮我解决这个问题

Answer 1

查看提供的示例，您似乎在 Flutter 的 build 阶段获得了 Future。

FutureBuilder 的 documentation明确指出这将导致重复调用提供的 Future:

The future must have been obtained earlier, e.g. during State.initState, State.didUpdateConfig, or State.didChangeDependencies. It must not be created during the State.build or StatelessWidget.build method call when constructing the FutureBuilder. If the future is created at the same time as the FutureBuilder, then every time the FutureBuilder's parent is rebuilt, the asynchronous task will be restarted.

基本上，每次 Flutter 渲染管道重建您的 widget 时，您都会初始化新的 getAllCategories() 调用。

避免这种影响的推荐方法是在 State.initState、State.didUpdateConfig 或 State.didChangeDependencies 中初始化 Future。