使用线程时发生InvalidOperationException

Question

I got InvalidOperationException in my Forms application. I create new thread in button click event method:

private void btn_Start_Click(object sender, EventArgs e)
{
    Thread thread = new Thread(new ThreadStart(() =>
    {
        presenter.RunAlgorithm();
    }));

    thread.Start();

}

There is the code when I got exception:

public string Distance
    {
        get { return cbo_DistanceMeasure.SelectedValue.ToString(); }
    }

This property get selected by user value of comboBox. Then this value is used in presenter class in method RunAlgorithm(). I read that for this kind of exception I must use Thread-Safe Calls to controls, like in this article: How to: Make Thread-Safe Calls to Windows Forms Controls . But how use this in my scenario, when I used MVP pattern with Properties to set-get controls value ? Is possible to use delegate with Properties, because I've got more properties which work with controls.

Answer 1

The problem is you're trying to access control from a different thread - its not allowed. In Windows Forms you need to do this:

public string Distance
{
    get
    {
        if(this.InvokeRequired)
        {
            return (string)this.Invoke(new Func<string>(this.GetDistance));
        }

        return this.GetDistance();
    }
}

string GetDistance()
{
    return cbo_DistanceMeasure.SelectedValue.ToString();
}

---

WPF:

private void btn_Start_Click(object sender, EventArgs e)
{
    string selectedValue = Dispatcher.Invoke(() => cbo_DistanceMeasure.SelectedValue.ToString(), DispatcherPriority.Background);

    //Do something with the value here, maybe set your property value?
}

You can also do directly from property if it can access Dispatcher

public string Distance
{
    get
    {
        return Dispatcher.Invoke(() => cbo_DistanceMeasure.SelectedValue.ToString(), DispatcherPriority.Background);
    }
}