为什么在此代码中多次运行MessageBox？

Question

I'm a newbie in programming and writing codes. I have a very simple form with 6 buttons. When I click on every button only the sender's text got Magenta. But Button3 do a further work and that's opening a "Hello" messageBox. The problem is when I click on Button3, it shows "hello" string 4 times. Why? I think and expect it show it just once no more.

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private void Typhok(object sender, EventArgs e)
    {
        foreach (Control x in this.Controls)
        {
            if (x.Equals(sender))
                x.ForeColor = Color.Magenta;
            else
                x.ForeColor = Color.Black;
        }
        b3.Click += new EventHandler(Popup);
    }

    private void Popup(object sender, EventArgs e)
    {
        MessageBox.Show("hello!");
    }
}

UPDATE: Can anyone explain to me why that original code had that problem?

Answer 1

Register event handler in constructor, not in Typhok method. The final code should look like:

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        b3.Click += new EventHandler(Popup);
    }

    private void Typhok(object sender, EventArgs e)
    {
        foreach (Control x in this.Controls)
        {
            if (x.Equals(sender))
                x.ForeColor = Color.Magenta;
            else
                x.ForeColor = Color.Black;
        }
    }

    private void Popup(object sender, EventArgs e)
    {
       MessageBox.Show("hello!");
    }
}