Flutter實現文字捲動高亮效果的範例講解

class StringParser {
  // 匯入的文字
  final String content;
  // 高亮部分尾部索引, 也就是兩段的區分位置
  final int endIndex;

  StringParser({required this.content, required this.endIndex});

  late StringScanner _scanner;

  // 解析函數
  InlineSpan parser() {
    _scanner = StringScanner(content);

    parseContent();

    final List<InlineSpan> spans = [];

    int currentPosition = 0;

    // 需要高亮的部分
    spans.add(TextSpan(style: _spans.style, text: _spans.text(content)));
    currentPosition = _spans.end;

    // 未高亮的部分
    if (currentPosition != content.length) {
      spans.add(
          TextSpan(text: content.substring(currentPosition, content.length)));
    }

    return TextSpan(style: TextStyleSupport.defaultStyle, children: spans);
  }

  late SpanBean _spans;

  // 解析需要變成高亮的字元
  void parseContent() {
    int startIndex = 0;

    _spans = SpanBean(startIndex, endIndex);

    if (!_scanner.isDone) {
      _scanner.position++;
    }
  }
}

class SpanBean {
  SpanBean(this.start, this.end);

  final int start;
  final int end;

  String text(String src) {
    return src.substring(start, end);
  }

  TextStyle get style => TextStyleSupport.highLightStyle;
}

class TextStyleSupport {
  static const defaultStyle = TextStyle(color: Colors.black, fontSize: 36);
  static const highLightStyle = TextStyle(color: Colors.green, fontSize: 36);
}

_starPlay(flag) {
	// flag用於判斷是 執行還是暫停
    if (this.endIndex == content.length + 1 || !flag) {
      return;
    }

    parser = StringParser(content: content, endIndex: this.endIndex++);
    span = parser.parser();

    setState(() {});
    Future.delayed(Duration(milliseconds: 100)).then((value) {
      _starPlay(this.flag);
    });
  }

import 'package:flutter/material.dart';
import 'string_parser.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',
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key? key}) : super(key: key);
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  late InlineSpan span;

  final String content =
      """一點不錯，」狐狸說。「對我來說，你還只是一個小男孩，就像其他千萬個小男孩一樣。我不需要你。你也同樣用不著我。對你來說，我也不過是一隻狐狸，和其他千萬只狐狸一樣。但是，如果你馴服了我，我們就互相不可缺少了。對我來說，你就是世界上唯一的了；我對你來說，也是世界上唯一的了。""";

  late StringParser parser;
  int endIndex = 0;
  bool flag = true;

  @override
  void initState() {
    super.initState();
    parser = StringParser(content: content, endIndex: endIndex);
    span = parser.parser();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text("捲動高亮文字"),
          actions: [
            ElevatedButton(
                onPressed: () {
                  this.flag = true;
                  _starPlay(flag);
                  print('開始');
                },
                child: Text("開始")),
            ElevatedButton(
                onPressed: () {
                  this.flag = false;
                  // _starPlay(flag);
                  print('暫停');
                },
                child: Text("暫停"))
          ],
        ),
        body: Padding(
          padding: const EdgeInsets.all(20.0),
          child: Text.rich(span),
        ));
  }

  _starPlay(flag) {
    if (this.endIndex == content.length + 1 || !flag) {
      return;
    }

    parser = StringParser(content: content, endIndex: this.endIndex++);
    span = parser.parser();

    setState(() {});
    Future.delayed(Duration(milliseconds: 100)).then((value) {
      _starPlay(this.flag);
    });
  }
}