Question

Hi
I see following code:

void UpdateMessage (string message)
{
    Action action = () => txtMessage.Text = message;
    this.Invoke (action);
}

Why using Action and then invoke action here? Why not just using txtMessage.Text = message to replace the code in function body?

---

Update

A fuller version of the code, presented in a comment, reproduced below with syntax highlighting, indentation etc.

public partial class Form1 : Form 
{ 
    public Form1() 
    { 
        InitializeComponent(); 
        new Thread(Work).Start(); 
    } 

    void Work() 
    { 
        Thread.Sleep(5000); 
        UpdateMessage("My Garden"); 
    } 

    void UpdateMessage(string message) { 
        Action action = () => textBox1.Text = message; 
        this.Invoke(action); 
    } 
} 

Answer 1

Because this code runs on a different thread from the UI and must be marshalled across to the UI thread with Invoke.

The documentation for Control.Invoke() states:

Executes the specified delegate on the thread that owns the control’s underlying window handle.

This is all necessary because the underlying Windows framework requires that operations on a window handle are performed by the thread that owns the window handle.