将监听器附加到scrollController

Question

我正在使用Flutter中的DraggableScrollableSheet，并想知道该表是否已折叠或展开。DraggableScrollableSheet的构建器提供了一个scrollController，我将其附加到监听器上。

我看到了这个有用的指南，但他们创建了一个ScrollController，而在我的情况下，scrollController由构造函数提供。我不明白如何获得他们相同的行为。

这是我的代码：

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SizedBox.expand(
        child: myBottomSheet()
      ),
    );
  }
}

class myBottomSheet extends StatefulWidget{
  @override
  _myBottomSheetState createState() => _myBottomSheetState();
}

class _myBottomSheetState extends State<myBottomSheet> {
  double appbarSize=0.08;
  @override
  Widget build(BuildContext context) {
    return DraggableScrollableSheet(
      maxChildSize: 0.8,
      minChildSize: appbarSize,
      initialChildSize: appbarSize,
      builder: (BuildContext context, ScrollController scrollController) {
        scrollController.addListener(_scrollListener); // <----------------
        return Container(
          child: ListView.builder(
            controller: scrollController,
            itemCount: 25,
            itemBuilder: (BuildContext context, int index) {
              return ListTile(title: Text('Item $index'));
            },
          ),
        );
      },
    );
  }

  _scrollListener(){
    //use controller such in the guide
  }

- Damien

Answer 1

您只需要重构代码。将您的_scrollListener方法在builder中定义。

如下所示：

class _myBottomSheetState extends State<myBottomSheet> {
  double appbarSize=0.08;
  @override
  Widget build(BuildContext context) {
    return DraggableScrollableSheet(
      maxChildSize: 0.8,
      minChildSize: appbarSize,
      initialChildSize: appbarSize,
      builder: (BuildContext context, ScrollController scrollController) {
        _scrollListener(){
         //use controller such in the guide
        }

        scrollController.addListener(_scrollListener); // <----------------
        return Container(
          child: ListView.builder(
            controller: scrollController,
            itemCount: 25,
            itemBuilder: (BuildContext context, int index) {
              return ListTile(title: Text('Item $index'));
            },
          ),
        );
      },
    );
  }

- Victor Eronmosele

---

这看起来非常不对：（1）你应该只在initState中添加一次监听器（你在每次调用build时都添加了一个监听器！你可能会为同一个控制器添加数百个监听器！）；（2）你需要在dispose中处理监听器。 - Luke Hutchison