How can I get the filename of a "module could not be found" error dialog

Question

When our C# app is missing a dependency it reports this "module could not be found" error dialog. Unfortunately this dialog does not include the name of the file it could not find. In this case the missing dependency was a DirectX dll D3DCompiler_43.dll. If a customer reports "module could not be found" it's not very helpful, but if they reported the name of the file not found it gives us at least a clue.

Can we catch this exception and produce an error dialog which includes the name of the file that wasn't found? Since it happens early in application startup (before main I believe) how can we do this?

Answer 1

Try subscribing to the AssemblyResolve event which is fired when the application cannot locate a required assembly. In the handler of this event you can provide your own message box containing the name of the assembly and any other info you like.

public static void Main()
{            
     AppDomain.CurrentDomain.AssemblyResolve += new ResolveEventHandler(AssemblyNotFoundEventHandler);

     InvokeExternalType();
}

private static Assembly ResolveEventHandler(object sender, ResolveEventArgs args)
{
    MessageBox.Show("Error, can't find assembly: " + args.Name, "Error", MessageBoxButtons.AbortRetryIgnore, MessageBoxIcon.Error);
    return null;
}

private static void InvokeExternalType()
{
    MyClass doc = ... // from an external assembly.
}

There is one hitch where the external type (that might belong to a missing assembly) must not be used in the main method or else the event won't be fired. It has to be called further in your code in a separate method as shown in the code sample above.

Answer 2

If you can modify the code and redeploy:

• Create a new startup class (one with Main()), make sure you choose that class in project properties
• Ensure there are no "using" and external references from your startup class outside System
• put a try/catch around a call to your previous startup class's Main

• print out the exception and all inner exceptions in a message box (or debug log)

  public class MyNewEntryClass{

  public static void Main(){

    try{
        MyPreviousEntryClass.Main();
    } catch (Exception x){
       Exception ix = x;
       while (ix!=null){
          MessageBox.Show("Exception: "+ix);
          ix=ix.InnerException;
       }
    }
  

  } }

EDIT: I see your exception is coming from a message handler. The above code edit can (and should) be applied to all entry methods, which includes all event handlers that handle events from outside your code. The above crash screen could show up for exceptions in various handlers, asynchronously executed code. For example a button handler with asynchrounous calls should have two try/catches to prevent the crash window from showing up:

private void Button_Clicked(object sender, EventArgs arg){
    try{
        Action<string> asyncCall = (s)=>{
            try{
                //...exception here will cause crash  
                // as it's not handled in Button_Clicked
            } catch (Exception xOnAsyncThread){
            }
        };
        asyncCall.BeginInvoke("outahere",null,null);
    } catch (Exception xOnUIThread){
    }
}

The above statement is true for windows message handling as well - it's just another event handler for an outside event

If you can't modify the code and redeploy use Sysinternals Process Monitor: http://technet.microsoft.com/en-us/sysinternals/bb896645 Configure it to monitor your app and highlight file not found events (see their docs for details)

If ProcessMonitor is too much copy all the contents from the exception message and go by exclusion - the ones that are loaded aren't the problem

Answer 3

Make you customer run depends.exe on your exe, save the results into a file and send this file to you.

Answer 4

I don't think you can do this programmatically. However, if you have access to the machine you can turn on a "global flag" to show what's called "Loader Snaps" (Show loader snaps (Windows Debuggers)) at least to identify the problem.

Here is an article about it that explains how to do it: Debugging LoadLibrary Failures

Answer 5

There is a "Fuison Log" which could be turned on by setting few registry entries. It helps to identify any kind of assembly loading issues. All you will need is the log files from the customer's PC.
Please see https://stackoverflow.com/a/1527249/1288776 for the details.
In case the link is not available:
Add the following values to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Fusion

DWORD ForceLog set value to 1
DWORD LogFailures set value to 1
DWORD LogResourceBinds set value to 1
String LogPath set value to folder for logs ie) C:\FusionLog\

Make sure you include the backslash after the Folder name and that the Folder exists.