Make button click work for once - vb.net

Question

How can I tell the code to not to write the word to textbox for every click on the button?
When both checkboxes are clicked both, text must be written in adding order but when I click the button again text shouldn't be doubled or multiplied.
Public Class Form1
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
If CheckBox1.Checked = True Then
TextBox1.Text += ("hello ")
End If
If CheckBox2.Checked = True Then
TextBox1.Text += ("please help")
End If
End Sub
End Class

Answer 1

Use a Boolean variable for each if statement, i.e. each check box. Set them to false initially and change your code to look something like this
If CheckBox1.Checked = True And CheckBox1Bool = False Then
TextBox1.Text += ("hello ")
CheckBox1Bool = True
End If
If CheckBox2.Checked = True And CheckBox2Bool = False Then
TextBox1.Text += ("please help")
CheckBox2Bool = True
End If
EDIT:
Public Class Form1
Dim Bool1 As Boolean
Dim Bool2 As Boolean
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
If CheckBox1.Checked = True And Not Bool1 Then
TextBox1.Text += ("hello ")
Bool1 = True
End If
If CheckBox2.Checked = True And Not Bool2 Then
TextBox1.Text += ("please help")
Bool2 = True
End If
End Sub
End Class
This works and as you can see I haven't changed the code only added in what I suggested to you.

Answer 2

Just reset your Checkbox.Checked event in your Button Click event. That way it will not send the text again till you reselect it.
Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
If CheckBox1.Checked = True Then
CheckBox1.Checked = False
TextBox1.Text += ("hello ")
End If
If CheckBox2.Checked = True Then
CheckBox2.Checked = False
TextBox1.Text += ("please help")
End If
End Sub

Answer 3

Thank you very much for your concern about my problem. after i checked your solutions i went to bed. i released stg just i was going to sleep and opened pc again and solved my silly problem with this thing.. this works perfect for me :)
Public Class Form1
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Textbox1.Text= ("")
If CheckBox1.Checked = True Then
TextBox1.Text += ("hello ")
End If
If CheckBox2.Checked = True Then
TextBox1.Text += ("please help")
End If
End Sub
End Class