演练 dotnet 使用 GeneratedComInterface 源代码生成方式调用 COM 接口

官方文档：

• ComWrappers source generation - .NET Microsoft Learn
• Using the ComWrappers API - .NET Microsoft Learn

本文将演练在 WPF 应用里面手动写 COM 调用的方式，调用打开文件对话框。访问 COM 的方式为源代码生成器方式

本文内容里面只给出关键代码片段，如需要全部的项目文件，可到本文末尾找到本文所有代码的下载方法

必要的基础库安装：

    <PackageReference Include="Microsoft.Windows.CsWin32" Version="0.3.106"><PrivateAssets>all</PrivateAssets><IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets></PackageReference>

编写 NativeMethods.txt 添加 Win32 方法调用

CoInitializeEx
CoCreateInstance
CoGetClassObject

上述逻辑详细请看 dotnet 使用 CsWin32 库简化 Win32 函数调用逻辑

编写 IFileOpenDialog 接口，代码如下

using System.Runtime.InteropServices;
using System.Runtime.InteropServices.Marshalling;namespace NearnearfayyerchodaiHikelahuhaw;[GeneratedComInterface(Options = ComInterfaceOptions.ComObjectWrapper)]
[Guid("d57c7288-d4ad-4768-be02-9d969532d960")]
internal partial interface IFileOpenDialog
{void Show(IntPtr owner);
}

在 MainWindow 的 Loaded 事件调用，代码如下

using System.Runtime.CompilerServices;
using System.Runtime.InteropServices.Marshalling;
using System.Runtime.InteropServices;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using Windows.Win32.System.Com;
using System.Runtime.Versioning;
using System.Windows.Interop;namespace NearnearfayyerchodaiHikelahuhaw;public partial class MainWindow : Window
{public MainWindow(){InitializeComponent();Loaded += MainWindow_Loaded;}private unsafe void MainWindow_Loaded(object sender, RoutedEventArgs e){//Windows.Win32.PInvoke.CoInitializeEx(null, COINIT.COINIT_APARTMENTTHREADED | COINIT.COINIT_DISABLE_OLE1DDE);var cw = new StrategyBasedComWrappers();var rclsid = Guid.Parse("DC1C5A9C-E88A-4dde-A5A1-60F82A20AEF7");var riid = Guid.Parse("d57c7288-d4ad-4768-be02-9d969532d960");void* ppv;var hr = CoCreateInstance(&rclsid, IntPtr.Zero,CLSCTX.CLSCTX_ALL, &riid, &ppv);hr.ThrowOnFailure();var fileOpenDialog = (IFileOpenDialog) cw.GetOrCreateObjectForComInstance(new IntPtr(ppv), CreateObjectFlags.None);var windowInteropHelper = new WindowInteropHelper(this);fileOpenDialog.Show(windowInteropHelper.Handle);}[DllImport("OLE32.dll", ExactSpelling = true)][DefaultDllImportSearchPaths(DllImportSearchPath.System32)][SupportedOSPlatform("windows5.0")]internal static extern unsafe Windows.Win32.Foundation.HRESULT CoCreateInstance(global::System.Guid* rclsid, IntPtr pUnkOuter, Windows.Win32.System.Com.CLSCTX dwClsContext, global::System.Guid* riid, void* ppv);
}

运行代码，即可看到弹出打开文件对话框

由于当前正在 WPF 线程里执行 Loaded 事件的逻辑，因此 CoInitializeEx 是可不调用的。在 WPF 框架内部已经帮忙调用了

以上代码重新定义 CoCreateInstance 是为了获取 ppv 指针

以上的 IFileOpenDialog 将生成以下代码

// <auto-generated />
#pragma warning disable CS0612, CS0618
file unsafe class InterfaceInformation : global::System.Runtime.InteropServices.Marshalling.IIUnknownInterfaceType
{public static global::System.Guid Iid { get; } = new([136, 114, 124, 213, 173, 212, 104, 71, 190, 2, 157, 150, 149, 50, 217, 96]);public static void** ManagedVirtualMethodTable => null;
}[global::System.Runtime.InteropServices.DynamicInterfaceCastableImplementationAttribute]
file unsafe partial interface InterfaceImplementation : global::NearnearfayyerchodaiHikelahuhaw.IFileOpenDialog
{[global::System.CodeDom.Compiler.GeneratedCodeAttribute("Microsoft.Interop.ComInterfaceGenerator", "9.0.11.11010")][global::System.Runtime.CompilerServices.SkipLocalsInitAttribute]void global::NearnearfayyerchodaiHikelahuhaw.IFileOpenDialog.Show(nint owner){var(__this, __vtable_native) = ((global::System.Runtime.InteropServices.Marshalling.IUnmanagedVirtualMethodTableProvider)this).GetVirtualMethodTableInfoForKey(typeof(global::NearnearfayyerchodaiHikelahuhaw.IFileOpenDialog));int __invokeRetVal;{__invokeRetVal = ((delegate* unmanaged[MemberFunction]<void*, nint, int> )__vtable_native[3])(__this, owner);}// NotifyForSuccessfulInvoke - Keep alive any managed objects that need to stay alive across the call.global::System.Runtime.InteropServices.Marshal.ThrowExceptionForHR(__invokeRetVal);global::System.GC.KeepAlive(this);}
}file unsafe partial interface InterfaceImplementation
{
}file unsafe partial interface InterfaceImplementation
{
}namespace NearnearfayyerchodaiHikelahuhaw
{[global::System.Runtime.InteropServices.Marshalling.IUnknownDerivedAttribute<InterfaceInformation, InterfaceImplementation>]internal partial interface IFileOpenDialog{}
}namespace NearnearfayyerchodaiHikelahuhaw
{internal partial interface IFileOpenDialog{}
}

本文代码放在 github 和 gitee 上，可以使用如下命令行拉取代码。我整个代码仓库比较庞大，使用以下命令行可以进行部分拉取，拉取速度比较快

先创建一个空文件夹，接着使用命令行 cd 命令进入此空文件夹，在命令行里面输入以下代码，即可获取到本文的代码

git init
git remote add origin https://gitee.com/lindexi/lindexi_gd.git
git pull origin 333ee4d7f57cdecc80be1835a210a5d39a00d8a6

以上使用的是国内的 gitee 的源，如果 gitee 不能访问，请替换为 github 的源。请在命令行继续输入以下代码，将 gitee 源换成 github 源进行拉取代码。如果依然拉取不到代码，可以发邮件向我要代码

git remote remove origin
git remote add origin https://github.com/lindexi/lindexi_gd.git
git pull origin 333ee4d7f57cdecc80be1835a210a5d39a00d8a6

获取代码之后，进入 WPFDemo/NearnearfayyerchodaiHikelahuhaw 文件夹，即可获取到源代码

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