缓存MEF组件

Question

有没有办法缓存每个应用程序启动（WPF）的MEF组件图，就像MAF一样，以避免在每次应用程序启动时发现目录并构建组件图。为了加快我的应用程序启动速度。 MAF使用AddinsStore存储所有插件，当新插件发现存储重建并再次保存时。使用MEF设计的模块化应用程序可以做到这一点吗？

修改

在我的项目架构中我有扩展，模块和托管服务所以我有不同的导出像（IExtension，IModule，IManagedService），我处理所有组件的开始依赖项，我想要的是ex（扩展目录）包含许多dll，可能并非所有dll都包含（exports / Imports），因为某些dll只引用了一些Extensions。所以MEF的默认发现行为是在Extension Directory中的所有程序集中搜索exports / Imports，但我想通过查看所有dll并捕获类型及其名称和dll以在其中使用它们来修改此行为下一个启动时间。从catch直接加载组件（Exports），以便MEF知道可用组件及其位置，而无需加载和搜索dll。它看起来像是一个Exports及其Places和依赖项的字典，可以直接从它的地方（dll）获取实例。

Answer 1

我不知道这是否会100％帮助你，但是使用这段代码，我可以控制模块的加载顺序。

如果您可以控制加载顺序，则可以将所有* .dll放在同一个文件夹中并节省一些时间，在子文件夹中找到它们：

关键是使用这个额外的属性：[ExportMetadata("Order", 1)]

然后你的插件应该是这样的：

 [Export(typeof(YourContract))]
  [ExportMetadata("Order", 1)]
  public class YourPlugin: YourContract{}

为了按正确的顺序加载内容，你需要这样的东西：

<强>接口

public interface IOrderMetadata {
    [DefaultValue(int.MaxValue)]
    int Order {
      get;
    }
  }

<强> AdaptingCollection：

 public class AdaptingCollection<T, M> : ICollection<Lazy<T, M>>, INotifyCollectionChanged {
    /// <summary>
    /// Constructor</summary>
    public AdaptingCollection()
        : this(null) {
    }

    /// <summary>
    /// Constructor</summary>
    /// <param name="adaptor">Function to apply to items in the collection</param>
    public AdaptingCollection(Func<IEnumerable<Lazy<T, M>>, IEnumerable<Lazy<T, M>>> adaptor) {
      this._mAdaptor = adaptor;
    }

    /// <summary>
    /// CollectionChanged event for INotifyCollectionChanged</summary>
    public event NotifyCollectionChangedEventHandler CollectionChanged;

    /// <summary>
    /// Force the adaptor function to be run again</summary>
    public void ReapplyAdaptor() {
      if (this._mAdaptedItems == null) return;
      this._mAdaptedItems = null;
      this.OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
    }

    #region ICollection Implementation

    /// <summary>
    /// Returns whether the item is present in the collection</summary>
    /// <remarks>Accessors work directly against adapted collection</remarks>
    /// <param name="item">Item to look for</param>
    /// <returns>True if the item is in the collection</returns>
    public bool Contains(Lazy<T, M> item) {
      return this.AdaptedItems.Contains(item);
    }

    /// <summary>
    /// Copies the entire list to a one-dimensional array, starting at the specified index of the target array</summary>
    /// <remarks>Accessors work directly against adapted collection</remarks>
    /// <param name="array">The target array</param>
    /// <param name="arrayIndex">The starting index</param>
    public void CopyTo(Lazy<T, M>[] array, int arrayIndex) {
      this.AdaptedItems.CopyTo(array, arrayIndex);
    }

    /// <summary>
    /// Gets the number of items in the collection</summary>
    /// <remarks>Accessors work directly against adapted collection</remarks>
    public int Count => this.AdaptedItems.Count;

    /// <summary>
    /// Gets whether the collection is read only.</summary>
    /// <remarks>Accessors work directly against adapted collection</remarks>
    public bool IsReadOnly => false;

    /// <summary>
    /// Gets an enumerator for the collection</summary>
    /// <remarks>Accessors work directly against adapted collection</remarks>
    /// <returns>The IEnumerator</returns>
    public IEnumerator<Lazy<T, M>> GetEnumerator() {
      return this.AdaptedItems.GetEnumerator();
    }

    IEnumerator IEnumerable.GetEnumerator() {
      return this.GetEnumerator();
    }

    /// <summary>
    /// Add an item to the collection</summary>
    /// <remarks>Mutation methods work against complete collection and then force
    /// a reset of the adapted collection</remarks>
    /// <param name="item">The item to add</param>
    public void Add(Lazy<T, M> item) {
      this._mAllItems.Add(item);
      this.ReapplyAdaptor();
    }

    /// <summary>
    /// Clear all items from the collection</summary>
    /// <remarks>Mutation methods work against complete collection and then force
    /// a reset of the adapted collection</remarks>
    public void Clear() {
      this._mAllItems.Clear();
      this.ReapplyAdaptor();
    }

    /// <summary>
    /// Remove an item from the collection</summary>
    /// <remarks>Mutation methods work against complete collection and then force
    /// a reset of the adapted collection</remarks>
    /// <param name="item">The item to remove</param>
    /// <returns>True if the item was found, otherwise false</returns>
    public bool Remove(Lazy<T, M> item) {
      bool removed = this._mAllItems.Remove(item);
      this.ReapplyAdaptor();
      return removed;
    }

    #endregion

    /// <summary>
    /// Invoke the adaptor function on the collection</summary>
    /// <param name="collection">The collection to adapt</param>
    /// <returns>The adapted collection</returns>
    protected virtual IEnumerable<Lazy<T, M>> Adapt(IEnumerable<Lazy<T, M>> collection) {
      if (this._mAdaptor != null) {
        return this._mAdaptor.Invoke(collection);
      }

      return collection;
    }

    /// <summary>
    /// Fire the CollectionChanged event</summary>
    /// <param name="e">Event args</param>
    protected virtual void OnCollectionChanged(NotifyCollectionChangedEventArgs e) {
      this.CollectionChanged?.Invoke(this, e);
    }

    private List<Lazy<T, M>> AdaptedItems => this._mAdaptedItems ?? (this._mAdaptedItems = this.Adapt(this._mAllItems).ToList());

    private readonly List<Lazy<T, M>> _mAllItems = new List<Lazy<T, M>>();
    private readonly Func<IEnumerable<Lazy<T, M>>, IEnumerable<Lazy<T, M>>> _mAdaptor;
    private List<Lazy<T, M>> _mAdaptedItems;

  }

<强> OderingCollection

public class OrderingCollection<T, M> : AdaptingCollection<T, M> {
    /// <summary>
    /// Constructor</summary>
    /// <param name="keySelector">Key selector function</param>
    /// <param name="descending">True to sort in descending order</param>
    public OrderingCollection(Func<Lazy<T, M>, object> keySelector, bool descending = false)
        : base(e => descending ? e.OrderByDescending(keySelector) : e.OrderBy(keySelector)) {
    }
  }

<强>用法

[ImportMany(typeof(YourContract), AllowRecomposition = true)] 
    internal OrderingCollection<YourContract, IOrderMetadata> Plugins{
      get; private set;
    }

在构造函数中：

this.Plugins= new OrderingCollection<ITemplateMapper, IOrderMetadata>(
                           lazyRule => lazyRule.Metadata.Order);

我的加载代码（可能与您的不同）：

private void LoadModules() {
      var aggregateCatalog = new AggregateCatalog();
      aggregateCatalog.Catalogs.Add(new DirectoryCatalog(".", "*.Plugin.*.dll"));
      var container = new CompositionContainer(aggregateCatalog);
      container.ComposeParts(this);     
    }

我希望这可以帮助你摆脱MAF