Flutter MIDI合成器插件flutter_midi_synth的使用

开始使用

本项目是一个用于Flutter的插件包起点，专门包含针对Android和/或iOS平台的特定实现代码。

获取帮助

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完整示例代码

以下是使用flutter_midi_synth插件的完整示例代码：

import 'dart:io';
import 'dart:async';

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:flutter_midi_synth/flutter_midi_synth.dart';
import 'package:flutter/foundation.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatefulWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {

  final midiSynth = FlutterMidiSynth();

  String _platformVersion = 'Unknown';
  String _value = 'assets/Piano.sf2'; // SoundFont文件路径
  var dura = <double>[0.25, 0.5, 1, 1.5, 2, 3]; // 音符持续时间
  var whiteKeys = <List<int>>[]; // 白键音符编号

  @override
  void initState() {
    load(_value); // 加载SoundFont文件
    super.initState();
    initPlatformState(); // 初始化平台状态
  }

  void load(String asset) async {
    print('Loading File...');
    ByteData _byte = await rootBundle.load(asset); // 加载SoundFont文件
    midiSynth.prepare(sf2: _byte, name: _value.replaceAll('assets/', '')); // 准备MIDI合成器

    // 初始化白键音符编号
    var whiteIDs = [0, 2, 4, 5, 7, 9, 11];
    for (var i = 1, x = 0; i < 6; i++) {
      var temp = <int>[];
      for (var j = 0; j < 7; j++, x += 16) {
        var keyNum = i * 12 + whiteIDs[j] + 24; // 计算音符编号
        temp.add(keyNum);
      }
      whiteKeys.add(temp);
    }
  }

  // 平台消息异步初始化
  Future<void> initPlatformState() async {
    String platformVersion;
    try {
      platformVersion =
          await FlutterMidiSynth.platformVersion ?? 'Unknown platform version';
    } on PlatformException {
      platformVersion = 'Failed to get platform version.';
    }

    if (!mounted) return;

    setState(() {
      _platformVersion = platformVersion;
    });
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: const Text('Plugin example app'),
        ),
        body: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          crossAxisAlignment: CrossAxisAlignment.center,
          mainAxisSize: MainAxisSize.max,
          children: [
            Text('Running on: $_platformVersion\n'), // 显示平台版本
            ElevatedButton(onPressed: () { play(); }, child: Text('playTrack')), // 播放音轨
            ElevatedButton(onPressed: () { click(1, 2, 6); }, child: Text("middle c")), // 点击中间C音符
          ],
        ),
      ),
    );
  }

  // 播放音轨
  void play() {
    var track = [
      [3, 3, 4],
      [5, 3, 2],
      [1, 3, 2],
      [7, 2, 2],
      [6, 2, 2],
      [1, 3, 2],

      [5, 3, 5],
      [-1, -1, 3],
      [1, 3, 2],
      [2, 3, 2],

      [3, 3, 4],
      [6, 3, 2],
      [5, 3, 2],
      [3, 3, 2],
      [2, 3, 2],
      [1, 3, 1],

      [3, 3, 6],
      [5, 3, 2],
      [6, 3, 2],
      [6, 3, 2],

      [6, 3, 4],
      [5, 3, 2],
      [7, 2, 2],
      [7, 2, 1],
      [6, 2, 1],
      [7, 2, 2],
      [1, 3, 2],

      [2, 3, 6],
      [3, 3, 2],
      [5, 3, 2],

      [3, 3, 3],
      [5, 3, 2],
      [3, 3, 2],
      [2, 3, 2],
      [2, 3, 1],
      [2, 3, 1],
      [1, 3, 2],
      [6, 2, 2],

      [1, 3, 5],
      [-1, -1, 3],
      [5, 2, 3],
    ];

    for (var i = 0; i < track.length; i++) {
      var temp = track[i];
      click(temp[0], temp[1], temp[2]);
    }
  }

  // 点击音符并播放
  void click(var numKey, var level, var duration) {
    if (numKey == -1) {
      // 如果numKey为-1，则暂停一段时间
      sleep(Duration(milliseconds: (dura[duration - 1] * 500).toInt()));
      return;
    }
    midiSynth.playMidiNote(midi: whiteKeys[level][numKey - 1]); // 播放音符
    sleep(Duration(milliseconds: (dura[duration - 1] * 500).toInt())); // 等待音符时长
    midiSynth.stopMidiNote(midi: whiteKeys[level][numKey - 1]); // 停止音符
  }
}

代码说明

1. load方法

加载SoundFont文件，并将其准备到MIDI合成器中：

void load(String asset) async {
  print('Loading File...');
  ByteData _byte = await rootBundle.load(asset);
  midiSynth.prepare(sf2: _byte, name: _value.replaceAll('assets/', ''));
}

2. click方法

播放指定的音符，并在一定时间后停止：

void click(var numKey, var level, var duration) {
  if (numKey == -1) {
    sleep(Duration(milliseconds: (dura[duration - 1] * 500).toInt()));
    return;
  }
  midiSynth.playMidiNote(midi: whiteKeys[level][numKey - 1]);
  sleep(Duration(milliseconds: (dura[duration - 1] * 500).toInt()));
  midiSynth.stopMidiNote(midi: whiteKeys[level][numKey - 1]);
}

3. play方法

播放一个音轨，包含多个音符：

void play() {
  var track = [
    [3, 3, 4],
    [5, 3, 2],
    ...
  ];
  for (var i = 0; i < track.length; i++) {
    var temp = track[i];
    click(temp[0], temp[1], temp[2]);
  }
}