Flutter：ListView不滚动，不反弹

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 {

  @override
  Widget build(BuildContext context) {
    return new ListView(
      children: [
        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的行为与预期的一样。我可以滚动到视口之外，并且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 {
  ScrollController _cOntroller= new ScrollController();

  @override
  Widget build(BuildContext context) {
    return new ListView(
      controller: _controller,
      children: [
        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，将无法再滚动。为什么在添加ScrollController时无法再滚动？同样添加physics: new BouncingScrollPhysics(),到ListView也无济于事。

谢谢你的帮助 ：）

To always have the scroll enabled on a ListView you can wrap the original scroll phisics you want with the AlwaysScrollableScrollPhysics class. More details here. If you want you can specify a parent or rely on the default.

Here is your example with the option added:

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 {
  ScrollController _cOntroller= new ScrollController();

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