2021-04-21 17:33:28 -04:00
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using System;
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using System.Collections;
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using System.Collections.Generic;
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using Vanara.PInvoke;
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namespace Vanara.Collections
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{
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/// <summary>A generic interface to identify matching COM enumerator interfaces</summary>
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/// <typeparam name="TElem">The type of the elem.</typeparam>
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public interface ICOMEnum<TElem>
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{
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/*
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/// <summary>Retrieves the specified number of items in the enumeration sequence.</summary>
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/// <param name="celt">
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/// The number of items to be retrieved. If there are fewer than the requested number of items left in the sequence, this method
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/// retrieves the remaining elements.
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/// </param>
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/// <param name="rgelt">
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/// <para>An array of enumerated items.</para>
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/// <para>
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/// The enumerator is responsible for calling AddRef, and the caller is responsible for calling Release through each pointer
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/// enumerated. If celt is greater than 1, the caller must also pass a non-NULL pointer passed to pceltFetched to know how many
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/// pointers to release.
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/// </para>
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/// </param>
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/// <param name="pceltFetched">
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/// The number of items that were retrieved. This parameter is always less than or equal to the number of items requested.
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/// </param>
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/// <returns>If the method retrieves the number of items requested, the return value is S_OK. Otherwise, it is S_FALSE.</returns>
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HRESULT Next(uint celt, TElem[] rgelt, out uint pceltFetched);
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/// <summary>Skips over the specified number of items in the enumeration sequence.</summary>
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/// <param name="celt">The number of items to be skipped.</param>
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/// <returns>If the method skips the number of items requested, the return value is S_OK. Otherwise, it is S_FALSE.</returns>
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HRESULT Skip(uint celt);
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/// <summary>Resets the enumeration sequence to the beginning.</summary>
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/// <remarks>
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/// There is no guarantee that the same set of objects will be enumerated after the reset operation has completed. A static
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/// collection is reset to the beginning, but it can be too expensive for some collections, such as files in a directory, to
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/// guarantee this condition.
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/// </remarks>
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void Reset();
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*/
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}
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/// <summary>
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/// Creates an enumerable class from a get next method in the form of HRESULT Next(uint, TItem[], out uint) and a reset method. Useful
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/// if a class doesn't support <see cref="IEnumerable"/> or <see cref="IEnumerable{T}"/> like some COM objects.
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/// </summary>
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/// <typeparam name="TItem">The type of the item.</typeparam>
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2021-12-20 12:51:04 -05:00
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public class IEnumFromCom<TItem> : IEnumFromNext<TItem> where TItem : new()
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2021-04-21 17:33:28 -04:00
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{
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private readonly ComTryGetNext cnext;
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/// <summary>Initializes a new instance of the <see cref="IEnumFromNext{TItem}"/> class.</summary>
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/// <param name="next">The method used to try to get the next item in the enumeration.</param>
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/// <param name="reset">The method used to reset the enumeration to the first element.</param>
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public IEnumFromCom(ComTryGetNext next, Action reset) : base()
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{
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if (next is null || reset is null)
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throw new ArgumentNullException();
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cnext = next;
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base.next = TryGet;
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base.reset = reset;
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}
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/// <summary>
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/// Delegate that gets the next value in an enumeration and returns true or returns false to indicate there are no more items in the enumeration.
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/// </summary>
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/// <param name="celt">The number of items requested.</param>
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/// <param name="rgelt">An array of items to be returned.</param>
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/// <param name="celtFetched">The number of items retrieved in the <paramref name="celt"/> parameter.</param>
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/// <returns>
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/// This method supports the following return values: S_OK = The number of items returned is equal to the number specified in the
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/// <paramref name="celt"/> parameter. S_FALSE = The number of items returned is less than the number specified in the <paramref
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/// name="celt"/> parameter.
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/// </returns>
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public delegate HRESULT ComTryGetNext(uint celt, TItem[] rgelt, out uint celtFetched);
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/// <summary>Initializes a new instance of the <see cref="IEnumFromCom{TItem}"/> class from a COM enumeration interface instance.</summary>
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/// <param name="enumObj">The COM enumeration interface instance.</param>
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public static IEnumFromCom<TItem> Create<TIntf>(TIntf enumObj) where TIntf : class, ICOMEnum<TItem>
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{
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if (enumObj is null)
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throw new ArgumentNullException(nameof(enumObj));
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var cew = new ComEnumWrapper<TIntf>(enumObj);
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return new IEnumFromCom<TItem>(cew.ComObjTryGetNext, cew.ComObjReset);
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}
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private bool TryGet(out TItem item)
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{
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2021-12-20 12:51:04 -05:00
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var res = new TItem[] { new TItem() };
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2021-04-21 17:33:28 -04:00
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item = default;
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if (cnext(1, res, out var ret) != HRESULT.S_OK)
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return false;
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item = res[0];
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return true;
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}
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private class ComEnumWrapper<T> where T : class, ICOMEnum<TItem>
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{
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private readonly T obj;
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public ComEnumWrapper(T o) => obj = o;
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public void ComObjReset() => ComInvoke("Reset");
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public HRESULT ComObjTryGetNext(uint celt, TItem[] rgelt, out uint celtFetched)
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{
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var para = new object[] { celt, rgelt, 0U };
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var hr = (HRESULT)ComInvoke("Next", para);
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celtFetched = (uint)para[2];
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return hr;
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}
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private object ComInvoke(string meth, object[] p = null) => typeof(T).GetMethod(meth).Invoke(obj, p);
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}
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}
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}
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