如何在颤动中自动滚动文本？

Question

我想要实现的是一个多行文本，它将以固定速度自动滚动到列表末尾。

这是一个不同的应用程序，它做类似的事情。无论如何要在颤振中做到这一点？

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {
  ScrollController _scrollController = ScrollController();
  _scrollToBottom() {
    _scrollController.animateTo(_scrollController.position.maxScrollExtent,
        duration: Duration(seconds: 30), curve: Curves.linear);
  }

  @override
  Widget build(BuildContext context) {
    WidgetsBinding.instance.addPostFrameCallback((_) => _scrollToBottom());
    String val = '''
BUNCH OF TEXT HERE.
''';
    return Scaffold(
      appBar: AppBar(
        title: Text('Lyrics'),
      ),
      body: SingleChildScrollView(
        controller: _scrollController,
        child: Text(
          val,
          maxLines: 1000,
        ),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

我在自动滚动中添加了一堆lorem ipsum文本。以一定的速度到达底部。在当前设置中，文本会在 30 秒内自动滚动到底部。

但我想要的是一个按钮，我可以按下它来开始这个滚动。如果可能的话，用速度代替时间。

编辑：随着答案下方的文字确实滚动。但我遇到的问题是，如果我进行任何手动干预，滚动就会停止。有没有办法在不再次按下按钮的情况下恢复滚动？

提前致谢。

Answer 1

添加了一个名为speedFactor. 增加它会增加滚动速度，反之亦然。

当我们向底部滚动时，具有恒定的持续时间会降低速度。这是因为我们试图在同一持续时间内覆盖不同的距离，这意味着您的速度必须有所不同。

所以为了处理这个问题，我正在调整持续时间以保持恒定的速度因素。

double maxExtent = _scrollController.position.maxScrollExtent;
double distanceDifference = maxExtent - _scrollController.offset;
double durationDouble = distanceDifference / speedFactor;

为了停止动画，我只是animateTo当前offset会停止动画，因为我们已经在偏移处，没有什么可以动画的了。

这是一个工作示例

import 'package:flutter/material.dart';
import 'dart:async';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

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

class _MyHomePageState extends State<MyHomePage> with TickerProviderStateMixin {
  ScrollController _scrollController = ScrollController();
  bool scroll = false;
  int speedFactor = 20;

  _scroll() {
    double maxExtent = _scrollController.position.maxScrollExtent;
    double distanceDifference = maxExtent - _scrollController.offset;
    double durationDouble = distanceDifference / speedFactor;

    _scrollController.animateTo(_scrollController.position.maxScrollExtent,
        duration: Duration(seconds: durationDouble.toInt()),
        curve: Curves.linear);
  }

  _toggleScrolling() {
    setState(() {
      scroll = !scroll;
    });

    if (scroll) {
      _scroll();
    } else {
      _scrollController.animateTo(_scrollController.offset,
          duration: Duration(seconds: 1), curve: Curves.linear);
    }
  }

  @override
  Widget build(BuildContext context) {
    String val = '''
BUNCH OF TEXT HERE. BUNCH OF TEXT HERE. BUNCH OF TEXT HERE. BUNCH OF TEXT HERE. BUNCH OF TEXT HERE. BUNCH OF TEXT HERE. BUNCH OF TEXT HERE. BUNCH OF TEXT HERE. BUNCH OF TEXT HERE.BUNCH OF TEXT HERE.BUNCH OF TEXT HERE.BUNCH OF TEXT HERE.BUNCH OF TEXT HERE.BUNCH OF TEXT HERE.BUNCH OF TEXT HERE. BUNCH OF TEXT HERE.v 
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''';
    return Scaffold(
      appBar: AppBar(
        title: Text('Lyrics'),
      ),
      body: NotificationListener(
        onNotification: (notif) {
          if (notif is ScrollEndNotification && scroll) {
            Timer(Duration(seconds: 1), () {
              _scroll();
            });
          }

          return true;
        },
        child: SingleChildScrollView(
          controller: _scrollController,
          child: Text(
            val,
            maxLines: 1000,
          ),
        ),
      ),
      floatingActionButton: FloatingActionButton(onPressed: () {
        _toggleScrolling();
      }), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

更新：添加了使滚动视图在用户中断后继续滚动的代码。