mobile - 如何自动滚动文本？

我要实现的是一种多行文本，它将以固定的速度自动滚动直到列表的结尾。

这是一个执行类似操作的不同应用程序。反正有什么办法做到这一点？

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.
    );
  }
}

我添加了许多lorem ipsum文本来自动滚动。以一定的速度到达底部。在当前设置中，文字会在30秒内自动滚动到底部。

但是我想要的是一个可以按下以开始滚动的按钮。如果可能的话，而不是时间，而要使用速度。

编辑:在下面的答案文本不会滚动。但是我遇到的问题是，如果我进行任何手动干预，滚动就会停止。有什么方法可以继续滚动而无需再次按下按钮？

提前致谢。

最佳答案

添加了一个名为speedFactor的变量。增加它会增加滚动速度，反之亦然。

当我们向底部滚动时，持续时间恒定会降低速度。这是因为我们试图在相同的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。

因此，为了解决这个问题，我正在调整持续时间以保持恒定的速度因数。

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

为了停止动画，我只是对当前的animateTo进行offset编码，由于我们已经处于偏移位置，因此没有动画可做，因此将停止动画。

这是一个有效的例子

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:添加了使用户中断后滚动 View 继续滚动的代码。