IOptionsMonitor 是一种单一示例服务，可随时检索当前选项值，，这在单一实例依赖项中尤其有用。IOptionsMonitor用于检索选项并管理TOption实例的选项通知， IOptionsMonitor 支持以下方案：

更改通知

命名选项

可重载配置

选择性选项失效 (IOptionsMonitorCache)

IOptionsMonitor public interface IOptionsMonitor<out TOptions> { /// <summary> /// 返回具有 DefaultName 的当前 TOptions 实例。 /// </summary> TOptions CurrentValue { get; } /// <summary> /// 返回具有给定名称的已配置的 TOptions 实例。 /// </summary> TOptions Get(string name); /// <summary> /// 注册一个要在命名 TOptions 更改时调用的侦听器。 /// </summary> IDisposable OnChange(Action<TOptions, string> listener); } OptionsMonitor

OptionsMonitor通过IOptionsChangeTokenSource实现监听事件

public class OptionsMonitor<TOptions> : IOptionsMonitor<TOptions>, IDisposable where TOptions : class, new() { private readonly IOptionsMonitorCache<TOptions> _cache; private readonly IOptionsFactory<TOptions> _factory; private readonly IEnumerable<IOptionsChangeTokenSource<TOptions>> _sources; private readonly List<IDisposable> _registrations = new List<IDisposable>(); internal event Action<TOptions, string> _onChange; /// <summary> /// Constructor. /// </summary> /// <param name="factory">The factory to use to create options.</param> /// <param name="sources">The sources used to listen for changes to the options instance.</param> /// <param name="cache">The cache used to store options.</param> public OptionsMonitor(IOptionsFactory<TOptions> factory, IEnumerable<IOptionsChangeTokenSource<TOptions>> sources, IOptionsMonitorCache<TOptions> cache) { _factory = factory; _sources = sources; _cache = cache; foreach (var source in _sources) { var registration = ChangeToken.OnChange( () => source.GetChangeToken(), (name) => InvokeChanged(name), source.Name); _registrations.Add(registration); } } private void InvokeChanged(string name) { name = name ?? Options.DefaultName; _cache.TryRemove(name); var options = Get(name); if (_onChange != null) { _onChange.Invoke(options, name); } } /// <summary> /// The present value of the options. /// </summary> public TOptions CurrentValue { get => Get(Options.DefaultName); } /// <summary> /// Returns a configured <typeparamref name="TOptions"/> instance with the given <paramref name="name"/>. /// </summary> public virtual TOptions Get(string name) { name = name ?? Options.DefaultName; return _cache.GetOrAdd(name, () => _factory.Create(name)); } /// <summary> /// Registers a listener to be called whenever <typeparamref name="TOptions"/> changes. /// </summary> /// <param name="listener">The action to be invoked when <typeparamref name="TOptions"/> has changed.</param> /// <returns>An <see cref="IDisposable"/> which should be disposed to stop listening for changes.</returns> public IDisposable OnChange(Action<TOptions, string> listener) { var disposable = new ChangeTrackerDisposable(this, listener); _onChange += disposable.OnChange; return disposable; } /// <summary> /// Removes all change registration subscriptions. /// </summary> public void Dispose() { // Remove all subscriptions to the change tokens foreach (var registration in _registrations) { registration.Dispose(); } _registrations.Clear(); } internal class ChangeTrackerDisposable : IDisposable { private readonly Action<TOptions, string> _listener; private readonly OptionsMonitor<TOptions> _monitor; public ChangeTrackerDisposable(OptionsMonitor<TOptions> monitor, Action<TOptions, string> listener) { _listener = listener; _monitor = monitor; } public void OnChange(TOptions options, string name) => _listener.Invoke(options, name); public void Dispose() => _monitor._onChange -= OnChange; } }

IOptionsChangeTokenSource 的代码片段：

public interface IOptionsChangeTokenSource<out TOptions> { IChangeToken GetChangeToken(); string Name { get; } }

在OptionsMonitor的构造函数中，通过调用其GetChangeToken方法，获取到 ChangeToken ，在 InvokeChanged 完成 *_onChange* 事件的调用:

private void InvokeChanged(string name) { name = name ?? Options.DefaultName; _cache.TryRemove(name); var options = Get(name); if (_onChange != null) { _onChange.Invoke(options, name); } }

对外暴露OnChange方法,方便我们添加自己的业务逻辑

public IDisposable OnChange(Action<TOptions, string> listener) { var disposable = new ChangeTrackerDisposable(this, listener); _onChange += disposable.OnChange; return disposable; }