Question

Trying to update my label from another thread through an interface and a delegate. In debug mode it says the label property is set to the message. But I see nothing at the form itself.

Working in .NET 4.0

A small representation of what I am using:

My Interface:

public interface IMessageListener
{
    void SetMessage(string message);
}

the form where I implement it:

public partial class Form1 : Form, IMessageListener
{
...
    public void SetMessage(string message)
    {
        SetControlPropertyValue(ColoLbl, "Text", message);
    }

    delegate void SetControlValueCallback(Control oControl, string propName, object propValue);
    private void SetControlPropertyValue(Control oControl, string propName, object propValue)
    {
        if (oControl.InvokeRequired)
        {
            SetControlValueCallback d = new SetControlValueCallback(SetControlPropertyValue);
            oControl.Invoke(d, new object[] { oControl, propName, propValue });
        }
        else
        {
            Type t = oControl.GetType();
            PropertyInfo[] props = t.GetProperties();
            foreach (PropertyInfo p in props.Where(p => p.Name.ToUpper() == propName.ToUpper()))
            {
                p.SetValue(oControl, propValue, null);
            }
        }
    }
 }

the class where I try to set the message through the interface. This class is being run from another thread:

public class Controller
{
    IMessageListener iMessageListener = new Form1();
    ...
    public void doWork()
    {
        iMessageListener.SetMessage("Show my message");
    }
 }

The code compiles all fine, when stepping through with debugging the property of the label does get set, it just doesn’t show on the form itself for some reason.

I suspect it’s either I am missing a line somewhere, or the way the Controller class handles the interface what causes the problem. But i can’t figure out why or what exactly.

Answer 1

The Text property of ColoLbl won’t change in the Form1 previously loaded when you call iMessageListener.SetMessage("Show my message"); in your code because iMessageListener was initialized as a new Form1();. It may only change in the new instance created.

IMessageListener iMessageListener = new Form1();

If you are trying to change ColoLbl value in Form1 which was initialized before, do not initialize a new instance of Form1. Instead, initialize an IMessageListener which links to the Form1 created previously.

Example

//myFormSettings.cs
class myFormSettings
{
    public static Form1 myForm1; //We will use this to save the Form we want to apply changes to
}

 

//Form1.cs
private void Form1_Load(object sender, EventArgs e)
{
    myFormSettings.myForm1 = this; //Set myForm1(the form we will control later) to this
    Form2 X = new Form2(); //Initialize a new instance of Form2 as X which we will use to control this form from
    X.Show(); //Show X
}

 

//Form2.cs
IMessageListener iMessageListener = myFormSettings.myForm1;
iMessageListener.SetMessage("Show my message");

Thanks,

I hope you find this helpful 🙂