C#

private volatile bool formClosed = false;

private void Form1_FormClosing(object sender, FormClosingEventArgs e)
{
    formClosed = true;
}

delegate void ProgressValueDelegate(int value); 
public void SetProgressValue(int value)
{
    if (this.InvokeRequired)
    {
       ProgressValueDelegate pvd = new ProgressValueDelegate(SetProgressValue);                
       this.Invoke(pvd, new object[] { value });
    }
    else
    {
       if( formClosed == false )
       {
           m_progressBar.Value = value;
       }
    }
}

HuntrCkr wrote:

you can also move the if

public void SetProgressValue(int value)
{
    if( formClosed == true )
    {
        return;
    }

    if (this.InvokeRequired)
    {
       ProgressValueDelegate pvd = new ProgressValueDelegate(SetProgressValue);                
       this.Invoke(pvd, new object[] { value });
    }
    else
    {
        m_progressBar.Value = value;
    }
}

Luc Pattyn wrote:

My mistake. You're right about the test, if it sits on the top of the method, it gets executed twice so it can't go wrong. However executing it twice all the time may be a high price to pay for potentially saving one thread switch when the form closes.

Luc Pattyn wrote:

I do not really agree on the BeginInvoke issue.

public void SetProgressValue(int value)
{
    MethodInvoker method = delegate
    {
        if (!formClosed)
        {
            m_progressBar.Value = value;
        }
    };
 
    if (InvokeRequired)
        BeginInvoke(method);
    else
        method.Invoke();
}