Question

I have a WPF application where the user enters database information in some textboxes. Once the user clicks “connect”, a connection string is created from what the user had entered and a connection is established. I noticed that if the user enters any info that is wrong, the application will hang until the connection times out. By hang, I mean the user can’t interact with the rest of the application at all.

It is my goal to keep the application responsive while the connection string is tested.

I thought that putting this workflow on a different thread is a good solution. My idea is to just disable anything that may need a database connection while the thread runs. Once the thread comes back (and has has confirmed the connection string to be valid) I would re-enable everything. Otherwise, leave everything disabled.

However, the Thread class doesn’t have an event notification when the thread is done (or at least I am unaware of one).

I have also worked with the BackgroundWorker class. This works better. However, when the RunWorkerCompletedEventHandler event is fired and the connection string isn’t valid, I get the following exception:

The calling thread cannot access this object because a different
thread owns it.

This is probably because the connection still hasn’t timed out when the completed event handler is fired.

Does anybody have any ideas, or should I just NOT try to multithread a connection to a database?

A code outline of what I am doing:

private void bw_DoWork(object sender, DoWorkEventArgs e)
{
    dbTool = new DBTool();
    // Create the connection string
    e.Result = dbTool.connectToDB(); // connectToDB() returns a bool (true if connection established)
}

private void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
    // connectToDB() returns a bool (true if connection established)
    if(e.Result == true)  // Trying to read e.Result here throws the exception
    {
        // e.Error and e.Cancel should be checked first
        // However, I would like the thread to finish before
        // this event is fired
    }
    if (e.Error != null)
    {
        Console.WriteLine(e.Error.Message);
    }
}

Answer 1

Thank you everyone for your input.

I was able to come up with a solution. After coming across Working With The WPF Dispatcher. I determined that you can obtain the UI thread’s Dispatcher object:

//...

dbTool = new DBTool();
// Initialize the connection string
// Disable some UI
Thread thread = new Thread(new ThreadStart(
        delegate()
        {
            dbTool.connectToDB();
            UIControl.Dispatcher.BeginInvoke(
              new Action(
                  update
            ));
        }
));
thread.Start();

//.....

void update()
{
    if (dbTool.validString)     // If the connection string was valid
    {
        // Re-enable controls
    }
    else     // Invalid connection string
    {
        // Keep controls disabled if no connection could be created
    }
}

This indeed will test the connection string on a different thread, leaving the rest of the application responsive.