CODEWITHSUNDEEP
c#invoke
Walt
Walt

Reputation: 332

invoke with multiple arguments resulting in FormatException

I'm trying to invoke a Form method from a different thread. In the form class, I have:

delegate int ReplaceMessageCallback(string msg, int key);

public int ReplaceMessage(string msg, int key)
{
    if (this.InvokeRequired)
    {
        ReplaceMessageCallback amc = new ReplaceMessageCallback(ReplaceMessage);
        object[] o = new object[] { msg, key };
        return (int)this.Invoke(amc, o);
    }
    bool found = false;
    int rv;

    lock (this)
    {
        if (key != 0)
        {
            found = RemoveMessage(key);
        }
        if (found)
        {
            rv = AddMessage(msg, key);
        }
        else
        {
            rv = AddMessage(msg);
        }
    }

    MainForm.EventLogInstance.WriteEntry((found) 
                        ? EventLogEntryType.Information 
                        : EventLogEntryType.Warning,
            IntEventLogIdent.MessageFormReplace1,
            String.Format("MessageForm::ReplaceMessage(({2},{0}) returns {1}.\n\n(The message {3} exist to be replaced.)",
                key,
                rv,
                msg,
                (found) 
                    ? "did" 
                    : "did not"));
    return rv;
}

When I run this, I get an exception "FormatException was unhandled" "Index (zero based) must be greater than or equal to zero and less than the size of the argument list." on the call to Invoke.

Essentially this same code fragment works fine on class methods that only take a single parameter, so I assume I'm doing something wrong with the object array but I have no idea what.

Upvotes: 0

Views: 306

Answers (2)

Walt
Walt

Reputation: 332

It turns out that the invoke call will pass along exceptions within the function it calls, and you can't step (F11 in debugger) into it. I assumed that it would step into the called code, so when it failed I thought it was the actual Invoke call.

I messed up a String.Format in the body of the function, and Invoke passed that exception to me with no indication of where in the code the problem actually happened.

Upvotes: 0

Jim Mischel
Jim Mischel

Reputation: 133995

An easier way to handle this is:

if (this.InvokeRequired)
{
    int rslt;
    this.Invoke((MethodInvoker) delegate
    {
        rslt = ReplaceMessage(msg, key);
    }
    return rslt;
}

Upvotes: 1

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