为什么我在Future builder里面无法修改PageView.builder的页面？

Question

你好，堆栈溢出我在未来构建器中使用pageview.builder时遇到了麻烦。它所翻阅的项目是卡片，我之前确实有这个功能，但在植入逻辑来获取笔记和其他东西时，我转而使用未来构建器，并将这个NoteSet移到它自己的类中。我坚持认为我在某个地方做了一个突破性的改变，但我不确定。奇怪的是，我可以构建并看到卡片。附带的手势检测器也能正常工作，但我不能在我的pageview.builder中翻页。

任何帮助是非常感激

class NoteSet extends StatefulWidget {
  VoidCallback callback;
  final Category category;

  NoteSet(this.category, this.callback);

  @override
  _NoteSetState createState() => _NoteSetState();
}

class _NoteSetState extends State<NoteSet> {
  List<NoteEntry> sortedNotes = [];
  double currentPage;
  bool largeCards = false;

  SortMethod currentSortMethod = SortMethod.CreatedDescending;

  Future<List<NoteEntry>> getNotes() async {
    return await readCategoryNotes(widget.category);
  }

  void sortNotes(){...}

  refresh() {...}

  deleteCategory() async {
    deleteCategoryDialog(context, widget.category, refresh);
  }

  void toggleModifiedSort(){
    currentSortMethod == SortMethod.ModifiedDescending ? currentSortMethod = SortMethod.ModifiedAscending : currentSortMethod = SortMethod.ModifiedDescending;
    refresh();
  }

  void toggleCreatedSort(){
    currentSortMethod == SortMethod.CreatedDescending ? currentSortMethod = SortMethod.CreatedAscending : currentSortMethod = SortMethod.CreatedDescending;
    refresh();
  }

  void toggleCardSize(){
    largeCards = !largeCards;
    refresh();
  }

  void moveThisCategoryUp() async {
    await moveCategoryUp(widget.category);
    refresh();
  }

  void moveThisCategoryDown() async {
    await moveCategoryDown(widget.category);
    refresh();
  }

  @override
  Widget build(BuildContext context) {
    PageController controller = PageController();
    currentPage = (sortedNotes.length - 1).roundToDouble();
    return Column(
      children: <Widget>[
        Padding(
          padding: EdgeInsets.symmetric(horizontal: 10.0),
          child: Row(
            mainAxisAlignment: MainAxisAlignment.spaceBetween,
            children: <Widget>[
              Text(widget.category.toString().split(".").last,
                style: TextStyle(
                  color: Colors.white,
                  fontSize: 46.0,
                  fontWeight: FontWeight.bold,
                  letterSpacing: 1.0,
                )
              ),
              PopupMenuButton<VoidCallback>(...),
            ],
          ),
        ),
        FutureBuilder(
          future: getNotes(),
          builder: (context, snapshot){
            if(snapshot.hasData){
              sortedNotes = snapshot.data;
              sortNotes();
              controller.addListener(() {
                setState(() {
                  currentPage = controller.page;
                });
              });
              return Column(
                children: <Widget>[
                  Padding(
                    padding: const EdgeInsets.only(left: 15.0),
                    child: Row(
                      children: <Widget>[
                        Text("${sortedNotes.length} Entries",
                            style: TextStyle(color: Colors.tealAccent[200]))
                      ],
                    ),
                  ),
                  Stack(
                    children: <Widget>[
                      CardScrollWidget(currentPage, sortedNotes, largeCards ? 0.8 : 1.2),
                      Positioned.fill(
                        child: GestureDetector(
                          onTap: () {
                            editNoteDialog(context, sortedNotes[currentPage.round()], refresh);
                          },
                          onLongPress: () {
                            deleteNoteDialog(context, sortedNotes[currentPage.round()], refresh);
                          },
                          child: ScrollConfiguration(
                            behavior: PageScrollBehavior(),
                            child: PageView.builder(
                              itemCount: sortedNotes.length,
                              controller: controller,
                              reverse: true,
                              itemBuilder: (context, index) {
                                return Container();
                              },
                            ),
                          ),
                        ),
                      )
                    ],
                  ),
                ],
              );
            }
            else{
              return Padding(
                padding: const EdgeInsets.all(20.0),
                child: Center(
                  child: SpinKitPulse(
                    color: Colors.tealAccent,
                    size: 60.0,
                  ),
                ),
              );
            }
          },
        ),
        SizedBox(height: 15,),
      ],
    );
  }
}

Answer 1

好吧，我找到了我的问题，每次NoteSet构建时，它都会将currentPage变量设置为初始页。我还去掉了future builder，改为在init时调用future，然后在发现数据时刷新。这是我修改后的代码。

class NoteSet extends StatefulWidget {
  VoidCallback callback;
  final Category category;

  NoteSet(this.category, this.callback);

  @override
  _NoteSetState createState() => _NoteSetState();
}

class _NoteSetState extends State<NoteSet> {
  List<NoteEntry> sortedNotes = [];
  double currentPage = 0;
  bool largeCards = false;
  bool dataReady = false;

  SortMethod currentSortMethod = SortMethod.CreatedDescending;

  Future getNotes() async {
    dataReady = false;
    refresh();
    sortedNotes = await readCategoryNotes(widget.category);
    currentPage = (sortedNotes.length - 1).roundToDouble();
    dataReady = true;
    refresh();
  }

  void sortNotes(){...}

  refresh() {
    widget.callback();
    this.setState((){});
    sortNotes();
  }

...

  @override
  void initState() {
    getNotes();
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: <Widget>[
        Padding(
          padding: EdgeInsets.symmetric(horizontal: 10.0),
          child: Row(
            mainAxisAlignment: MainAxisAlignment.spaceBetween,
            children: <Widget>[
              Text(widget.category.toString().split(".").last,
                style: TextStyle(
                  color: Colors.white,
                  fontSize: 46.0,
                  fontWeight: FontWeight.bold,
                  letterSpacing: 1.0,
                )
              ),
              PopupMenuButton<VoidCallback>(
                onSelected: (VoidCallback value){
                  value();
                },
                icon: Icon(
                  Icons.more_horiz,
                  size: 30.0,
                  color: Colors.white,
                ),
                itemBuilder: (BuildContext context) => <PopupMenuEntry<VoidCallback>>[...],
              ),
            ],
          ),
        ),
        ((){
            if(dataReady){
              PageController controller = PageController(initialPage: sortedNotes.length - 1);
              controller.addListener(() {
                setState(() {
                  currentPage = controller.page;
                });
              });
              return Column(
                children: <Widget>[
                  Padding(
                    padding: const EdgeInsets.only(left: 15.0),
                    child: Row(
                      children: <Widget>[
                        Text("${sortedNotes.length} Entries",
                            style: TextStyle(color: Colors.tealAccent[200]))
                      ],
                    ),
                  ),
                  Stack(
                    children: <Widget>[
                      CardScrollWidget(currentPage, sortedNotes, largeCards ? 0.8 : 1.2),
                      Positioned.fill(
                        child: GestureDetector(
                          onTap: () {
                            editNoteDialog(context, sortedNotes[currentPage.round()], refresh);
                          },
                          onLongPress: () {
                            deleteNoteDialog(context, sortedNotes[currentPage.round()], refresh);
                          },
                          child: ScrollConfiguration(
                            behavior: PageScrollBehavior(),
                            child: PageView.builder(
                              itemCount: sortedNotes.length,
                              controller: controller,
                              reverse: true,
                              itemBuilder: (context, index) {
                                return Container();
                              },
                            ),
                          ),
                        ),
                      )
                    ],
                  ),
                ],
              );
            }
            else{
              return Padding(
                padding: const EdgeInsets.all(20.0),
                child: Center(
                  child: SpinKitPulse(
                    color: Colors.tealAccent,
                    size: 60.0,
                  ),
                ),
              );
            }
          }()),
        SizedBox(height: 15,),
      ],
    );
  }
}