cannot add a reference .NET

Question

I have a DLL which I would like to add as a reference to my project, but everytime I try to do it a dialog pops up telling me:

The reference could not be added. Please make sure that the file is accesible, and that it is a valid assembly or COM component.

I have researched a little and found out that error is because the assembly is unmanaged by .NET and that I should use DLLImport Attribute, however, I have the same exact solution in another computer, and everythig just works fine.

The difference is that the new computer I'm trying to add the reference is x64 and the old one is x86.

I have both the x64 and x86 DLL's, and can't add any. Why is this happening?

you'll probably need DllImport and P/Invoke things as mentioned in the answers. — Bahamut
– Bahamut, Commented Mar 8, 2012 at 15:34

Thorsten Dittmar · Accepted Answer · 2012-03-08 15:25:15Z

14

You can not add unmanaged DLLs as references in Visual Studio, regardless of the 32/64 "bittyness". And I doubt that it worked on your x86 machine.

There's a difference between "normal" DLLs and COM-DLLs.

You can add a reference to a COM-DLL after it was registered with the system (actually you reference the exposed COM object and a reference to the DLL is added automatically). This can be done on the "COM"-Tab of the "Add reference" dialog (here you have to make sure that your project is built as a x86 target in most cases).

"normal" DLLs can - as I said - not be added at all. You can include them in the solution (right click solution, select "Add existing file"), but they will not be referenced unless you declare something like

[DllImport("...")]
public static extern void MyFunction();

I suspect that in your other solution, there's some kind of wrapper DLL, which you are actually referencing and which contains the DLL imports.

edited Mar 8, 2012 at 15:25

answered Mar 8, 2012 at 15:20

Thorsten Dittmar

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2 Comments

user710046 Over a year ago

I build to a custom dir like ../bin/ and place the required DLLs in that dir so my app can just see locate them by default. Simples!

Rajesh Kontham Over a year ago

I got the following exception: An attempt was made to load a program with an incorrect format. (Exception from HRESULT: 0x8007000B). ; File Details - DLL file: C++ Language, x64 built. Target: C#, x64 platform.

Uday0119 · Accepted Answer · 2012-03-08 15:32:17Z

There are multiple answeres to your question:

you may face this problem because the assembly you are trying to add is targeted and compiled for a x86 processor architecture. Just try change the Target Platform from x64 to x86 and even if that doent work, try change it to AnyCPU. AnyCPU Platform target makes your application executable on both types of architecture because it is architecture-free.
If the assembly happens to be a DLL, and it cannot be added as a reference, then it is not a COM as well as .NET assembly. It will be a native assembly like others (for example, shell32.dll, user32.dl etc). You have to use them via DllImport attribute, but you must first check the documentation of that dll to get the list of functions implemented in that dll.

Olivier Jacot-Descombes · Accepted Answer · 2012-03-08 15:27:00Z

2

Possibly the Type Library Importer (Tlbimp.exe) can help. It creates a wrapper .NET dll. The original COM DLL must still be there and must be registered! (Try to register it first, before trying it with TlbImp.)

If the 64-bit version does not work, set the platform target to x84 in your project build properties.

edited Mar 8, 2012 at 15:27

answered Mar 8, 2012 at 15:21

Olivier Jacot-Descombes

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Comments

squelos · Accepted Answer · 2012-03-08 15:25:34Z

1

Some DLL's cant be added as a reference, but however, they can still be used by C# with the famous [DllImport( params go here...)]

You might also have to inspect the dll in order to get the address of the functions you want to use . This can be achieved by using GetProcAddress

answered Mar 8, 2012 at 15:25

squelos

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Brainstroming · Accepted Answer · 2016-11-11 12:58:35Z

1

after trying to analyse the issue, I discover the following

[1] sometimes you see the reference in the reference manager, but you will not find the dll files in the mentioned directory where the Reference manager is not able to actualize the references.

[2] check the permission of your dll file.

answered Nov 11, 2016 at 12:58

Brainstroming

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Mou · Accepted Answer · 2022-05-24 10:19:15Z

0

My suggestion is to check if turning off C++ name mangling with extern "C".

I got the same DLL access error when I did not declare my DLL API with it.

For example, a "foo.h" should be:

extern "C"
{
__declspec( dllexport ) void foo();
}

Then we can call "foo()" in C# this way:

public const string DllName = "foo.dll";
[DllImport(DllName, EntryPoint = "foo", CallingConvention = CallingConvention.Cdecl, CharSet = CharSet.Ansi)]
public static extern void foo();

answered May 24, 2022 at 10:19

Mou

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Ben · Accepted Answer · 2012-03-08 15:20:04Z

-1

Try changing your Platform Target from Any CPU to x86. (project properties -> Build -> Platform Target)

answered Mar 8, 2012 at 15:20

Ben

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