自定義Configuration配置源

實現自定義配置源至少需要添加如下成員：

• 實現IConfigurationSource介面的配置源；
• 實現IConfigurationProvider介面或虛基類ConfigurationProvider的配置提供程式；
• 添加配置源的IConfigurationBuilder擴展方法；

如自定義一個TXT文本文件配置源：

添加配置源

配置源負責創建配置提供程式，以及監聽文件修改。監聽文件修改可以使用FileSystemWatcher，通過監聽Changed事件監聽配置文件的修改。使用ConfigurationReloadToken作為IChangeToken，當監聽到文件修改時調用取消令牌的取消操作，進而通知訂閱者文件已更改。

public class TxtConfigurationSource : IConfigurationSource, IDisposable
{
    private FileSystemWatcher? _fileWatcher;
    private ConfigurationReloadToken _reloadToken;

    public TxtConfigurationSource(string path, bool reloadOnChange = true)
    {
        FilePath = path;
        ReloadOnChange = reloadOnChange;
        _fileWatcher = new FileSystemWatcher(Directory.GetCurrentDirectory());
        _fileWatcher.Filter = "*.txt";
        _fileWatcher.EnableRaisingEvents = true;
        _fileWatcher.Changed += _fileWatcher_Changed;

        _reloadToken = new ConfigurationReloadToken();
    }

    private void _fileWatcher_Changed(object sender, FileSystemEventArgs e)
    {
        if (e.FullPath != FilePath)
            return;
        
        if (_reloadToken.HasChanged)
            return;

        // 觸發事件
        ConfigurationReloadToken previousToken = Interlocked.Exchange(ref _reloadToken, 
            new ConfigurationReloadToken());
        previousToken.OnReload();
    }

    public bool ReloadOnChange { get; set; }

    public string FilePath { get; set; }

    public IConfigurationProvider Build(IConfigurationBuilder builder)
    {
        return new TxtConfigurationProvider(this);
    }

    public IChangeToken GetChangeToken() => _reloadToken;

    public void Dispose() => Dispose(true);

    protected virtual void Dispose(bool disposing)
    {
        _fileWatcher?.Dispose();
    }
}

添加配置提供程式

配置提供程式負責載入配置文件，並訂閱配置源中的配置修改事件。通過ChangeToken.OnChange()方法進行事件訂閱，當監聽到文件改變時，重新載入文件：

public class TxtConfigurationProvider : ConfigurationProvider, IDisposable
{
    private readonly IDisposable _changeTokenRegistration;

    public TxtConfigurationProvider(TxtConfigurationSource source)
        :base()
    {
        Source = source ?? throw new ArgumentNullException(nameof(source));

        if (Source.ReloadOnChange)
        {
            _changeTokenRegistration = ChangeToken.OnChange(
                () => Source.GetChangeToken(),
                () =>
                {
                    Thread.Sleep(300);
                    Load();
                });
        }
    }

    public TxtConfigurationSource Source { get; }

    public override void Load()
    {
        if (!File.Exists(Source.FilePath))
            return;
        else
        {
            Data = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
            var lines = File.ReadAllLines(Source.FilePath);
            foreach (var line in lines)
            {
                var array = line.Replace("：", ":").Split(':');
                if (array.Length < 2)
                    continue;

                Data.Add(line.Substring(0, line.LastIndexOf(':')), array.Last());
            }
        }

        OnReload();
    }

    public void Dispose() => Dispose(true);

    protected virtual void Dispose(bool disposing)
    {
        _changeTokenRegistration?.Dispose();
    }
}

添加配置源擴展方法

添加IConfigurationBuilder擴展方法，方便將自定義配置源添加到IConfigurationBuilder中：

public static IConfigurationBuilder AddTxtFile(this IConfigurationBuilder builder, 
    string path, bool reloadOnChange)
{
    if (builder == null)
        throw new ArgumentNullException(nameof(builder));
    if (string.IsNullOrEmpty(path))
        throw new ArgumentException($"文件不能為空：{nameof(path)}");

    return builder.Add(new TxtConfigurationSource(path, reloadOnChange));
}

使用

首先通過擴展方法添加配置源，調用IConfigurationBuilder.Build()方法後即可通過IConfiguration獲取配置項。通過ChangeToken.OnChange()方法訂閱配置修改事件。

using ConfigurationTest;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Primitives;

IConfigurationBuilder configurationBuilder = new ConfigurationBuilder()
    .AddTxtFile(Path.Combine(Directory.GetCurrentDirectory(), "config.txt"), reloadOnChange: true);

// 通過IConfiguration直接讀取指定配置
IConfiguration configuration = configurationBuilder.Build();
Console.WriteLine($"FileProvider:Source:{configuration.GetSection("FileProvider:Source").Value}");
Console.WriteLine($"Provider:{configuration["FileProvider:Provider"]}");
Console.WriteLine();

// 通過綁定選項獲取配置
FileProviderOptions fileProviderOptions = new FileProviderOptions();
configuration.GetSection("FileProvider").Bind(fileProviderOptions);
Console.WriteLine($"FileProvider.Source = {fileProviderOptions.Source}");
Console.WriteLine($"FileProvider.Provider = {fileProviderOptions.Provider}");
Console.WriteLine();

// 監聽配置修改
var disable = ChangeToken.OnChange(() => configuration.GetReloadToken(),
                                   () =>
                                   {
                                       foreach (var section in configuration.GetChildren())
                                       {
                                           PrintAllConfig(section);
                                       }
                                       
                                       Console.WriteLine();
                                       Console.WriteLine("按“q”退出");
                                   });

Console.WriteLine("按“q”退出");
while (Console.ReadLine() != "q")
{
}

disable.Dispose();

void PrintAllConfig(IConfigurationSection config)
{
    var sections = config.GetChildren();
    if(sections == null || sections.Count() == 0)
        Console.WriteLine($"{config.Key} : {config.Value}");
    else
    {
        foreach (var section in sections)
        {
            PrintAllConfig(section);
        }
    }
}

class FileProviderOptions
{
    public string Source { get; set; }
    public string Provider { get; set; }
}

// config.txt
FileProvider:Source:TxtSource
FileProvider:Provider:TxtProvider