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    <p>The first issue I see is that Delphi's binary interface for function return values is different from that used by C# (and indeed every other major Windows compiler).</p> <p>So instead of using a function, use an <code>out</code> parameter.</p> <pre><code>procedure CreateMyDate(out Date: IMyDate); stdcall; begin Date := TMyDate.Create; end; </code></pre> <p>Then on the C# you can declare the function like this:</p> <pre><code>[DllImport(@"Project11.dll")] public static extern void CreateMyDate(out IMyDate Date); </code></pre> <p>Note that I removed a load of spurious parameters to your <code>DllImport</code> attribute. I guess you were adding them at random!</p> <p>The other issue is the interface. It needs to be declared as being a COM interface that supports <code>IUnknown</code>. Like this:</p> <pre><code>[ComImport, Guid("D032F796-167D-4B0D-851D-2AEEA226646A"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)] public interface IMyDate { void Analyze_Date(ref int y, int m, int d); } </code></pre> <p><strong>Update 1</strong></p> <p>The first problem with the updated question is something I failed to pick up in my original answer. The way the C# interface is declared means that that the marshaller assumes that the native functions all return <code>HRESULT</code> COM error codes. If the C# method has a return value then it is implicitly converted into an <code>out</code> parameter. There is a simple way to achieve this in Delphi. You replace <code>stdcall</code> with <code>safecall</code> on each method in the interface, and obviously in the implementation of that interface. Note that you should not change the calling convention of the <code>CreateMyDate</code> function.</p> <p>So your Delphi code should be like this:</p> <pre><code>IMyDate = interface ['{D032F796-167D-4B0D-851D-2AEEA226646A}'] Function testing():Boolean; safecall; end; TMyDate = Class(TInterfacedObject, IMyDate) Public Function testing():Boolean; safecall; End; </code></pre> <p>Another problem with the method in updated question is that C# marshals <code>bool</code> as a 4 byte value, but Delphi <code>Boolean</code> is just a single byte. This error is actually benign, but you can fix the problem by making the two sides of the interface match. For example:</p> <pre><code>[return: MarshalAs(UnmanagedType.U1)] bool testing(); </code></pre> <p>And I repeat what I said above. I removed spurious parameters from your <code>DllImport</code> attribute. In particular don't use <code>SetLastError</code> because your code is not setting the Win32 last error. Your <code>DllImport</code> should be exactly as per my answer. Don't confuse things by adding needless extra parameters to the attribute.</p> <p><strong>Update 2</strong></p> <p>You say in comments that you can't use <code>safecall</code> on the Delphi side. Which means that you need to suppress the <code>HRESULT</code> signature transformation on the C# side of the interface. That's done with <a href="http://msdn.microsoft.com/en-us/library/system.runtime.interopservices.preservesigattribute.aspx" rel="nofollow"><code>MethodImplOptions.PreserveSig</code></a>. You need to apply it to each method on your C# interface.</p> <pre><code>[ComImport, Guid("D032F796-167D-4B0D-851D-2AEEA226646A"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)] public interface IMyDate { [MethodImplAttribute(MethodImplOptions.PreserveSig)] void Analyze_Date(ref int y, int m, int d); [MethodImplAttribute(MethodImplOptions.PreserveSig)] [return: MarshalAs(UnmanagedType.U1)] bool testing(); } </code></pre> <p>This interface matches up with a Delphi interface declared like this:</p> <pre><code>IMyDate = interface ['{D032F796-167D-4B0D-851D-2AEEA226646A}'] procedure Analyze_Date(var y: Integer; m, d: Integer); stdcall; function testing(): Boolean; stdcall; end; </code></pre>
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    1. POInterface result delphi to c# - class define dll use in c#
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    1. USDavid Heffernan
    1. USDavid Heffernan
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    1. COhi thanks for answer and comments but if I whant change Interface delphi for Exaple: IMyDate = interface({IUnknown}IInvokable) ['{D032F796-167D-4B0D-851D-2AEEA226646A}'] Analize_Date(var y:integer; m,d:Integer); stdcall; end; and define procedure by Stdcall but i dont now how Define this Interface in C#?
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      1. USkhoshghadam
    2. COI'm surprised to see mixing P/Invoke and COM invocations in a Delphi C# interop scenario. Usually it's one or the other.
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      1. USJack G.
    3. CO@j. It allows you to expose an OOP like thing without full blown COM.
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      1. USDavid Heffernan
 

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