Delegates, Why? [duplicate]

Answer 1

One example where a delegate is needed is when you have to modify a control in the UI thread and you are operating in a different thread. For example,

public delegate void UpdateTextBox(string data);

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
    ...
    Invoke(new UpdateTextBox(textBoxData), data);
    ...

}

private void textBoxData(string data)
{
            textBox1.Text += data;
}