Flutter：ListView不可滚动，不可弹跳

我有以下示例（在 iPhone X、iOS 11 上测试）：

import 'package:flutter/material.dart';

void main() => runApp(new MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {

  @override
  Widget build(BuildContext context) {
    return new ListView(
      children: <Widget>[
        new Container(
          height: 40.0,
          color: Colors.blue,
        ),
        new Container(
          height: 40.0,
          color: Colors.red,
        ),
        new Container(
          height: 40.0,
          color: Colors.green,
        ),
      ]
    );
  }

}

在这种情况下，ListView 的行为与预期一致。我可以滚动到视口之外，ListView 会再次反弹（典型的 iOS 行为）。但是当我添加 ScrollController 来跟踪偏移量时，滚动的行为会发生变化：

import 'package:flutter/material.dart';

void main() => runApp(new MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  ScrollController _controller = new ScrollController();

  @override
  Widget build(BuildContext context) {
    return new ListView(
      controller: _controller,
      children: <Widget>[
        new Container(
          height: 40.0,
          color: Colors.blue,
        ),
        new Container(
          height: 40.0,
          color: Colors.red,
        ),
        new Container(
          height: 40.0,
          color: Colors.green,
        ),
      ]
    );
  }
}

在这种情况下，无法再进行滚动。为什么当我添加 ScrollController 后，滚动就不再可能了？还添加physics: new BouncingScrollPhysics(),到 ListView 没有帮助。

谢谢你的帮助 ：）

始终启用滚动ListView您可以用以下内容包装您想要的原始滚动物理AlwaysScrollableScrollPhysics班级。更多细节here https://docs.flutter.io/flutter/widgets/AlwaysScrollableScrollPhysics-class.html。如果您愿意，您可以指定parent或依赖默认值。

这是添加了选项的示例：

import 'package:flutter/material.dart';

void main() => runApp(new MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  ScrollController _controller = new ScrollController();

  @override
  Widget build(BuildContext context) {
    return new ListView(
        physics: const AlwaysScrollableScrollPhysics(), // new
        controller: _controller,
        children: <Widget>[
          new Container(
            height: 40.0,
            color: Colors.blue,
          ),
          new Container(
            height: 40.0,
            color: Colors.red,
          ),
          new Container(
            height: 40.0,
            color: Colors.green,
          ),
        ]
    );
  }
}