How can I resolve MATLAB Runtime's TypeInitializationException in a COM-registered WinForms control library?

Below is a summary of potential causes and workarounds to try:

Why the Error May Occur

When the control is instantiated inside an external host (like Excel) via COM, the MATLAB Runtime libraries may not be loaded or initialized in the same way as in a native Windows Forms or WPF App. In your case, the static initialization of MATLAB types (e.g. MWNumericArray and its dependency MWMCR) is failing because the dependent libraries (DLLs) that are normally found via the PATH may not be available to the process hosting the COM component.

Things to Check & Try

1. Process Environment (PATH)

   • Issue: Excel (or any external COM host) starts with its own process environment. Even if you have only one MATLAB Runtime installed and correctly added to PATH, Excel might have been launched before PATH changes were made.
   • Workaround: Restart the external application after setting the PATH to include the required MATLAB Runtime directories. In some cases, you may need to add these directories via a manifest or use registration‑free COM if possible.

2. Explicit Initialization of the MATLAB Runtime

   • Issue: The automatic static initialization (triggered by calling a constructor like MWNumericArray(0)) might be too early or not occur properly in the COM activation context.

   • Workaround: Try calling the MATLAB Runtime initialization explicitly early in your COM control’s lifecycle (for example, from an initialization method rather than a static constructor or the control’s constructor) so that you can catch and diagnose any issues.

   • Example:

     CSHARPCopied
     public void InitializeMATLABRuntime()
     {
         // This might invoke a function to pre-initialize the MWMCR
         // (Check your MATLAB Runtime documentation for the proper initialization call)
         try
         {
             var dummy = new MWNumericArray(0);
         }
         catch (Exception ex)
         {
             // Log or rethrow with more details
             throw new InvalidOperationException("Failed to initialize MATLAB Runtime.", ex);
         }
     }

3. Delayed or Lazy Loading

   • Issue: Early static construction of MATLAB types in your user control’s constructor might force a premature runtime initialization.
   • Workaround: Consider using lazy initialization (for example, using Lazy or deferring the creation of MWArray objects until after the control or COM host has fully loaded) to ensure all necessary environment variables and runtime dependencies are available.

4. Deployment and Assembly Dependencies

   • Issue: Ensure that all MATLAB Runtime assemblies and their dependent libraries are correctly placed or registered so that the COM host can resolve them.
   • Workaround: Double-check that the MATLAB Runtime’s bin directories are readable from the COM host process. In some cases you might need an app.config for the host (e.g., Excel.exe.config) to help the .NET runtime bind the required assemblies.

5. Platform and Version Consistency

   • Issue: Even though you are using a 64-bit configuration, double-check that the MATLAB Runtime library and your COM-registered control are both built for the same platform.
   • Workaround: Verify that there are no hidden 32‑bit/64‑bit mismatches. Since you’ve removed AnyCPU and use explicit 64‑bit builds, ensure that all dependent native libraries are also 64‑bit.

Next Steps

• Debug Logging: Enable fusion logging (or other assembly binding logs) to see if any dependent libraries aren’t being found when Excel loads your control.
• MATLAB Documentation & Support: Consult the MATLAB documentation on deploying components as COM objects. There may be special instructions or known issues for MATLAB Runtime usage in externally hosted controls.
• Isolation Test: Create a test COM control that does nothing but explicitly initialize MATLAB Runtime in a separate method (called after COM activation) to isolate the problem to initialization rather than control-specific code.

By addressing these areas, you should be able to determine why the MATLAB Runtime isn’t initializing correctly in your COM-registered control and apply the appropriate workaround.

Let me know if you need further specifics on any of these steps.