How to update textboxes in main thread from another thread?

Question

How you update textboxes and labels in the main thread from a new thread running a different class.

MainForm.cs (Main thread)

public partial class MainForm : Form
{
    public MainForm()
    {
        Test t = new Test();

        Thread testThread = new Thread(new ThreadStart(t.HelloWorld));
        testThread.IsBackground = true;
        testThread.Start();
    }

    private void UpdateTextBox(string text)
    {
        textBox1.AppendText(text + "\r\n");
    }

}

public class Test
{
    public void HelloWorld()
    {
        MainForm.UpdateTextBox("Hello World"); 
        // How do I execute this on the main thread ???
    }
}

I have looked at the examples on here but cant seem to get it right. Please could someone give some good links.

I have started again fresh so I don't mess up my code. If anyone would like to put up a working example with my example that would be great.

Also if I had to update multiple objects like textboxes and labels etc (not all at the same time) what would be the best way to go about it, having a method for each textbox or is there a way to do this with one method?

Answer 1

Invoke or BeginInvoke, e.g.

Invoke((MethodInvoker)delegate {
    MainForm.UpdateTextBox("Hello World"); 
});

---

@tiptopjones I guess you're asking also how to get a reference to the form. You could make your HelloWorld method take an object parameter, use the ParameterizedThreadStart delegate, and then pass a reference to the form as a parameter to the Thread.Start method. But I would suggest reading about anonymous methods which makes it a lot easier and keeps everything strongly typed.

public class MainForm : Form {
    public MainForm() {
        Test t = new Test();

        Thread testThread = new Thread((ThreadStart)delegate { t.HelloWorld(this); });
        testThread.IsBackground = true;
        testThread.Start();
    }

    public void UpdateTextBox(string text) {
        Invoke((MethodInvoker)delegate {
            textBox1.AppendText(text + "\r\n");
        });
    }
}

public class Test {
    public void HelloWorld(MainForm form) {
        form.UpdateTextBox("Hello World"); 
    }
}

When you get comfortable with that you could read up on lambda expressions and do it like:

Thread testThread = new Thread(() => t.HelloWorld(this));