Question

I’m trying to update a Ultragridrow cell in a background worker, but this is throwing a InvalidOperation Exception when this is called more than 1 time.

Here you have the method that starts the RunWorkerAsync.

    private void RefreshGridCacheStart()
    {
        try
        {
            if (this.uGridCache.Rows.Count == 0)
            {
                return;
            }

            if(!workerThread.IsBusy)
            {
                workerThread.DoWork += LookUpHostnames;
                workerThread.ProgressChanged += UpdateCacheHostCell;
                workerThread.RunWorkerCompleted += WorkerCompleted;
                workerThread.WorkerReportsProgress = true;
                workerThread.RunWorkerAsync();
            }
        }
        catch (Exception ex)
        {
            Debug.WriteLine(ex.Message + "\n" + ex.Source + "\n" + ex.ToString());
        }
    }

This is the DoWork method:

    private void LookUpHostnames(object sender, DoWorkEventArgs e)
    {
        var rowValues = new object[2];

        try
        {
            foreach (UltraGridRow row in uGridCache.Rows)//here is were I get an invalid operation exception
            {
                string cellValue = row.Cells["Host"].Text;
                if (Globals.cNet.isValidIP(cellValue))
                {
                    rowValues[0] = row;
                    rowValues[1] = cellValue;

                    workerThread.ReportProgress(0, rowValues);

                    string resolvedHostname = Globals.cIPLookup.LookupHostFromIP(cellValue);
                    rowValues[1] = resolvedHostname;

                    workerThread.ReportProgress(0, rowValues);
                }
            }
        }
        catch (Exception ex)
        {
            Debug.WriteLine(ex.Message + "\n" + ex.Source + "\n" + ex.ToString());
        }

    }

And this is the Report Progress method:

    private void UpdateCacheHostCell(object sender, ProgressChangedEventArgs e)
    {
        var rowValues = e.UserState as object[];
        var row = (UltraGridRow) rowValues[0];
        var sMesage = (string) rowValues[1];

        row.Cells["Host"].Value = sMesage;
    }

Answer 1

You can find your answer here Different question but ultimately the same problem. Your are changing data inside a foreach loop which invalidates the enumerator.
There are 2 possible solutions I see from reading your code

• Save all changes that need to be made to an List of changes and only report progress once after the foreach loop. This might not be a very good solution though since you are processing in the background. If there is other code running that could also change the data in the grid you would get the same error again.
• Since you are not adding rows you could easily change the foreach to a for loop. This might also lead to an issue if code on the main thread could add, or worse, remove rows