Question

I am quite new when it comes to threading but I am getting an InvalidOperationException when using the following code. I understand that it is trying to access importFileGridView but this was created by the UI thread which creates the exception. My question is, how do I resolve this? Is it possible for GetAllImports to have a return type? How do I access temp from my UI thread?

ThreadPool.QueueUserWorkItem(new WaitCallback(GetAllImports), null);

private void GetAllImports(object x)
    {
        DataSet temp = EngineBllUtility.GetAllImportFiles(connectionString);
        if (temp != null)
            importFileGridView.DataSource = temp.Tables[0];
        else
            MessageBox.Show("There were no results. Please try a different search", "Unsuccessful", MessageBoxButtons.OK, MessageBoxIcon.Information);
    }

Answer 1

You can’t change a user interface component on a background thread. In this case, setting the DataSource must be done on the UI thread.

You can handle this via Control.Invoke or Control.BeginInvoke, like so:

private void GetAllImports(object x)
{
    DataSet temp = EngineBllUtility.GetAllImportFiles(connectionString);
    if (temp != null)
    {
        // Use Control.Invoke to push this onto the UI thread
        importFileGridView.Invoke((Action) 
            () => 
            {
                importFileGridView.DataSource = temp.Tables[0];
            });
    }
    else
        MessageBox.Show("There were no results. Please try a different search", "Unsuccessful", MessageBoxButtons.OK, MessageBoxIcon.Information);
}