Question

I use a thread to execute some process on a machine. Eventually, the progress is reported back in an other thread. To update the GUI with the status of the process, I use a delegate like this:

public delegate void UpdateProgressDelegate(string description, int scriptnumber);
public void UpdateProgress(string description, int scriptnumber) {
    if (treeView.InvokeRequired) {
        treeView.Invoke(new UpdateProgressDelegate(UpdateProgress), description, scriptnumber);
        return;
    }
    // Update the treeview
}

And to call this delegate I use:

form.UpdateProgress("Ready", 3);

When the Invoke is called, I get a TargetParameterCountException: Parameter count mismatch.
I thought I could fix this by placing the string and int parameters in a single object like this:

public delegate void UpdateProgressDelegate(object[] updateinfo);
public void UpdateProgress(object[] updateinfo) {
    string description = (string) updateinfo[0];
    int scriptnumber = (int) updateinfo[1];
    if (treeView.InvokeRequired) {
        treeView.Invoke(new UpdateProgressDelegate(UpdateProgress), new object[] { description, scriptnumber });
        return;
    }       
    // Update the treeview
}

And to call it I use:

form.UpdateProgress(new object[] {"Ready", 3});

But this doesn’t work either. I keep getting the same TargetParameterCountException. Any ideas how I could fix this? Thanks in advance!

Answer 1

I would say: do it the easy way:

treeView.Invoke((MethodInvoker)delegate {
    UpdateProgress(description, scriptnumber);
});

or (equally):

treeView.Invoke((MethodInvoker) () => UpdateProgress(description, scriptnumber));

This gives you static-checking at the compiler, and IIRC MethodInvoker is checked explicitly, and called with Invoke() rather than DynamicInvoke(), making it faster too.

---

Re why it doesn’t work; in your example with:

public delegate void UpdateProgressDelegate(object[] updateinfo);

you are actually passing two parameters; to disambiguate and pass a single array to a params here, you need to double-wrap it:

treeView.Invoke(new UpdateProgressDelegate(UpdateProgress),
    new object[] { new object[] {description, scriptnumber }});

Basically, the outer array is the “array of all the parameters”, which contains a single element, which is the array that we wan’t to pass as the first parameter (updateinfo).