MissingMethodException - Can't find PInvoke DLL "TestDLL.dll" - Unable to invoke a function in imported DLL in C# mobile app.

Question

Hi,

I have a simple form application in C# that calls a function in an imported dll. I get a missingMethodException on calling that function. I have read all the related threads in the forum but nothing seems to be working for me.

Exception I get:

System.MissingMethodException was unhandled

  Message="Can't find PInvoke DLL 'TestDLL.dll'."

  StackTrace:

    at SmartDeviceProject1.Form1.button1_Click()

    at System.Windows.Forms.Control.OnClick()

    at System.Windows.Forms.Button.OnClick()

    at System.Windows.Forms.ButtonBase.WnProc()

    at System.Windows.Forms.Control._InternalWnProc()

    at Microsoft.AGL.Forms.EVL.EnterMainLoop()

    at System.Windows.Forms.Application.Run()

    at SmartDeviceProject1.Program.Main()

  InnerException: 

Here is my C# solution (Target device - Windows Mobile 6 Professional Device .NET CF 2.0) . It consists of two projects.

SmartDeviceProject1:

namespace SmartDeviceProject1

{

    public partial class Form1 : Form

    {

        public Form1()

        {

            InitializeComponent();

        }



        private void button1_Click(object sender, EventArgs e)

        {

            //displayString.Text = "test";

            displayString.Text  = Convert.ToString(NativeMethods.fnTestdll());

        }

    }



    internal abstract class NativeMethods

    {

        [DllImportAttribute("TestDLL.dll", EntryPoint = "fnTestdll", CallingConvention = CallingConvention.Winapi, SetLastError = false, CharSet = CharSet.Unicode)]

        public static extern int fnTestdll();

    }

}

Here are the testdll project files:

// Testdll.cpp : Defines the entry point for the DLL application.

//



#include "stdafx.h"

#include "Testdll.h"





BOOL APIENTRY DllMain( HANDLE hModule, 

                       DWORD  ul_reason_for_call, 

                       LPVOID lpReserved

					 )

{

	switch (ul_reason_for_call)

	{

	case DLL_PROCESS_ATTACH:

	case DLL_THREAD_ATTACH:

	case DLL_THREAD_DETACH:

	case DLL_PROCESS_DETACH:

		break;

	}

    return TRUE;

}



// This is an example of an exported variable

TESTDLL_API int nTestdll=0;



// This is an example of an exported function.

TESTDLL_API int fnTestdll(void)

{

	return 42;

}



// This is the constructor of a class that has been exported.

// see Testdll.h for the class definition

CTestdll::CTestdll()

{ 

	return; 

}

testdll.h

// The following ifdef block is the standard way of creating macros which make exporting 

// from a DLL simpler. All files within this DLL are compiled with the TESTDLL_EXPORTS

// symbol defined on the command line. this symbol should not be defined on any project

// that uses this DLL. This way any other project whose source files include this file see 

// TESTDLL_API functions as being imported from a DLL, whereas this DLL sees symbols

// defined with this macro as being exported.

#ifdef TESTDLL_EXPORTS

#define TESTDLL_API __declspec(dllexport)

#else

#define TESTDLL_API __declspec(dllimport)

#endif



// This class is exported from the Testdll.dll

class TESTDLL_API CTestdll {

public:

	CTestdll(void);

	// TODO: add your methods here.

};



extern TESTDLL_API int nTestdll;



TESTDLL_API int fnTestdll(void);

I have spend enough time on this, any help is greatly appreciated.

Thanks.

Answer 1

That can be because:

- You don't have this DLL in the correct location (which is either your main application location or \windows).
- DLL needs dependencies which are missing (e.g. MFC).
- DLL is compiled for wrong CPU.
- DLL does not export required entry points.

- Exported name is mangled.

 

You can use depends or dumpbin tools to check most of these issues. Use file explorer on device to check first one.

 

---

This posting is provided "AS IS" with no warranties, and confers no rights.

Answer 2

- I put the testdll.dll in main application location (on device) and also in \windows on device.
- DLL had a dependency on coredll.dll which depends.exe could not locate on my desktop. However, I see that coredll.dll in located in \windows on device.
- I am compiling for "platform: Windows mobile 6 Professional SDK ARMV4I" in Visual studio which is the same as my device's.
- Here is partial dumpbin output (seems like it does export the symbols).

  Section contains the following exports for Testdll.dll

    00000000 characteristics
    4A42615E time date stamp Wed Jun 24 10:24:46 2009
        0.00 version
           1 ordinal base
           4 number of functions
           4 number of names

    ordinal hint RVA      name

          1    0 00001060 ??0CTestdll@@QAA@XZ = ??0CTestdll@@QAA@XZ (public: __cdecl CTestdll::CTestdll(void))
          2    1 00001000 ??4CTestdll@@QAAAAV0@ABV0@@Z = ??4CTestdll@@QAAAAV0@ABV0@@Z (public: class CTestdll & __cdecl CTestdll::operator=(class CTestdll const &))
          3    2 00001048 ?fnTestdll@@YAHXZ = ?fnTestdll@@YAHXZ (int __cdecl fnTestdll(void))
          4    3 00003028 ?nTestdll@@3HA = ?nTestdll@@3HA (int nTestdll)

  Section contains the following imports:

    COREDLL.dll
              10003000 Import Address Table
              10002044 Import Name Table
                     0 time date stamp
                     0 Index of first forwarder reference

                      Ordinal    36

  

Answer 3

You must use DATA in def file or else the names of Your methods and classes will be mangled as mr Ilya Tumanov said .
Look under this discussion which I've done paralel with Yours.

---

If You'll find my answer satisfactory or helpful - mark it as answered! Thank You. PS. Votes also doesn't hurt :).

Answer 4

I tried that but it's of no avail. I put the TestDLL.dll file in the same location as programfiles\SmartDeviceProject3\ which contains SmartDeviceProject3.exe - my application.

testDLL.def

LIBRARY	"TestDLL"

EXPORTS

GetNumber		DATA

-----------------------------------------------------------------
TestDLL.cpp

#include "stdafx.h"


BOOL APIENTRY DllMain( HANDLE hModule, 
                       DWORD  ul_reason_for_call, 
                       LPVOID lpReserved
					 )
{
    return TRUE;
}

int GetNumber()
{
	return 42;
}

---------------------------------------------
C# code:

namespace SmartDeviceProject3
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            displayString.Text = Convert.ToString(NativeMethods.GetNumber());
        }
    }

    internal abstract class NativeMethods
    {
        [DllImportAttribute("TestDLL.dll", EntryPoint = "GetNumber")]
        public static extern int GetNumber();
    }
}

Answer 5

I see You don't like reading :). It should be like this:

C# code:

namespace SmartDeviceProject3

{

    public partial class Form1 : Form

    {

        [DllImport("testdll.dll", EntryPoint = "GetNumber")	

        private static extern int GetNumber();		



        public Form1()

        {

            InitializeComponent();

        }



        private void button1_Click(object sender, EventArgs e)

        {

            displayString.Text = Convert.ToString(GetNumber());

        }

    }

}

The rest is ok.

---

If You'll find my answer satisfactory or helpful - mark it as answered! Thank You. PS. Votes also doesn't hurt :).

Answer 6

It didn't help. Here is my latest attempt as you have suggested:

namespace SmartDeviceProject3
{
    public partial class Form1 : Form
    {
        [DllImport("testdll.dll", EntryPoint = "GetNumber")]
        private static extern int GetNumber();

        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            displayString.Text = Convert.ToString(GetNumber());
        }
    }
}

I tried to DllImport the coredll.dll and it is getting loaded and I am able to invoke a function in that DLL. which possibly means system DLLs don't have an issue with DllImport. Since mine is a test dll could there be anything related to security\signing? Should I disable security policy or something?

Answer 7

Hmm, maybe. Did You checked "Allow Unsafe Code" in application properties on C# side?

---

If You'll find my answer satisfactory or helpful - mark it as answered! Thank You. PS. Votes also doesn't hurt :).

Answer 8

Yes, tried that too. I just copy the testdll.dll to my device into the appropriate folders (i.e. where my <application>.exe resides and into the \windows folder). Is that enough or should I be doing anything extra? This is the first time I am writing a mobile app, so please bear with me if I ask fundamental questions.

Answer 9

Just one copy of testdll.dll next to Your application should do the trick.
Must be in the same folder as the .exe which is calling it.

I wonder where do You have problems, because I did it many times and I know it works in both emulator and device.
Maybe something is too obvious for me and I forgot to tell You about it... Hmm.

---

If You'll find my answer satisfactory or helpful - mark it as answered! Thank You. PS. Votes also doesn't hurt :).

Answer 10

Hello, this is my first post to a software dev. forum. Is it possible that a very long directory path to the native *.dll that I try to import, can cause problems?
 NOTE: I am running it through a simple windows mobile form via WM 6 Pro Emulator,  the current DLL path is %mylongprojectpath%/bin/debug/*.dll (on my windows Vista PC) and  I get the same MissingMethodException for PInvoke as mentioned previously.

Also: I used the following definition for writing my custom *.cpp file(which I saved as "Unicode" and compiled from VStudio command line with "/LD" option):
extern "C" __declspec(dllexport) string outmsg () {body of function returning a string message}

The Csharp definition I am trying to use it with is as below:

namespace

 

MobTest1 {

 

public partial class Form1 : Form {

[

DllImport("myseconddll22.dll")]

 

private static extern string CallNative();

 

public Form1() {

InitializeComponent();

}

 

 

private void button1_Click(object sender, EventArgs e){

 

MessageBox.Show(CallNative());

}

 

}

}

 

Very simple, yet I would really appreciate it if you could say what you think I should do since I am a complete beginner with PInvoke.
Thank you.

Answer 11

Please see possible solution for you in this thread:

http://www.eggheadcafe.com/forumpost.aspx?redirect=forumpostsubmission&topicid=16&forumpostid=10154965#Post10154965