Need help using Checkbox - vb.net

Question

i have a couple of questions about my basic project
if i have a check box and when its checked, it is going to a text box which is displaying the price, when i uncheck it my price still says in that text box, how can i make it dissapear as i uncheck the box?
Dim total As Double
If rb_s1.Checked = True Then
total += 650.0
txt_1.Text = total
thats my code.
and i have many combo boxes, how can i make them all add up as i check/uncheck them.

Answer 1

I would add this functionality into the CheckBox_Changed event handler. This way you can tell if it is unchecked or checked and add or subtract the value from price.
Private Sub CheckBox1_CheckedChanged(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles CheckBox1.CheckedChanged
If CheckBox1.Checked Then
total += 650.00
Else
total -= 650.00
End If
TextBox1.Text = total.ToString()
End Sub

Answer 2

You have to use Checked_Changed event of checkbox.
SHARED void CheckBox1_CheckedChanged(object sender, EventArgs e)
IF ChkBx.Checked = true then
textBox1.text = "1500"
else
textBox1.text = ""
END IF
END SUB

Answer 3

To get your displayed text to change when the state of your checkbox changes, you'll need to handle the CheckedChanged event. In Visual Studio while in Desginer mode for your form/control, you can select the check box control, and then in the Properties window, select the Events tab (the one with the little lightingbolt icon), and double click the CheckChanged event to stub in an event handler method AND attach the event to the handler.
ETA: I re-reading this, I'm not sure how clear I was. When I mentioned stubbing in the event handler and attaching the event to the handler, I meant that going the route of double-clicking the event in the designer will do this for you.
As an aside, it sounds like you want the text to be a sum of only the checked items, so from an architechtueral sense, I would recommend creating a single method to determine the sum, and have all check-box check events invoke that method rather than trying to make the event handler method itself do too much directly (maybe that was already clear to you).
So you might do something like this:
Public Class Form1
Private Sub DisplayTotal()
Dim total As Decimal = 0
If (CheckBox1.Checked) Then
total += Decimal.Parse(txtItem1.Text)
End If
'Add other items
txtTotal.Text = total
End If
End Sub
Private Sub CheckBox1_CheckedChanged(sender As System.Object, e As System.EventArgs) Handles CheckBox1.CheckedChanged
DisplayTotal()
End Sub
Private Sub CheckBox2_CheckedChanged(sender As System.Object, e As System.EventArgs) Handles CheckBox1.CheckedChanged
DisplayTotal()
End Sub
End Class