Question

I have a dependency on .NET 2.0 SP2 in my ClickOnce deployed application
(the ApplicationDeployment.CurrentDeployment.CheckForDetailedUpdate(false) method is SP2 only).

I would like to check whether SP2 is present during app startup. I have tried to detect this by catching MissingMethodException after calling a SP2-only method.

    /// <summary>
    /// The SP2 bootstrapper does not allow HomeSite installation
    /// http://msdn.microsoft.com/en-us/vstudio/bb898654.aspx
    /// So we only advice the user to download .NET 2.0 SP2 manually.
    /// </summary>
    private void CheckDotNet2SP()
    {
        WaitHandle wh = new AutoResetEvent(true);
        try
        {
            wh.WaitOne(1); //this method is .NET 2.0 SP2 only
        }
        //NOTE: this catch does not catch the MissingMethodException
        catch (Exception) //change to catch(MissingMethodException) does not help
        {
            //report that .NET 2.0 SP2 is missing
        }
        finally
        {
            wh.Close();
        }
    }

The code in catch never executes when this runs on .NET 2.0 without SP2. The exception is only caught by the AppDomain.CurrentDomain.UnhandledException event handler.

How is it possible that the MissingMethodException is not caught? I can imagine that this is a special case – the CLR hits a method that does not exist and somehow it is not possible to pass this to the catch block. I would like to understand the principle behind this.

Anyone has any resources on this issue? Are there any other exceptions that cannot be caught in a catch block?

Answer 1

I suspect it’s happening at JIT time, before the method is even properly entered – i.e. before your catch block is hit. It’s possible that if you catch MissingMethodException in the calling method, that will sort it out… particularly if you decorate CheckDotNet2SP with MethodImpl[MethodImplOptions.NoInlining]. It still sounds like it would be pretty dicey though.

You could always check for the presence of the method with reflection rather than by trying to call it though.