Default number in a text box - vb.net

Question

Foreword: This is code for a game.
On one of the forms on my VB program I have a large number of text boxes, the issue is regarding the following code:
Total_Gold.Text = (WoodPrice * TxtBoxWoodUnits.Text) + (MagicWoodPrice * TxtBoxMagicWoodUnits.Text) + (Pheonix_EggsPrice * TxtBoxPheonixEggsUnits.Text) + (MetalPrice * TxtBoxMetalUnits.Text) + (Dwarven_GemsPrice * TxtBoxDwarvenGemsUnits.Text) + (LeatherPrice * TxtBoxLeatherUnits.Text) + (Dragon_ScalesPrice * TxtBoxDragonScalesUnits.Text) + (Raw_SilverPrice * TxtBoxRawSilverUnits.Text) + (Raw_GoldPrice * TxtBoxRawGoldUnits.Text) + (DownPrice * TxtBoxDownUnits.Text) + (CottonPrice * TxtBoxCottonUnits.Text) + (QuicksilverPrice * TxtBoxQuicksilverUnits.Text) + (StonePrice * TxtBoxStoneUnits.Text) + (CoalPrice * TxtBoxCoalUnits.Text) + (ThreadPrice * TxtBoxThreadUnits.Text) + (FurPrice * TxtBoxFurUnits.Text)
This is contained in a timer event that shows how much it would cost the player to purchase all of the items. This works as intended, until the text box is blank. Each "section" draws information from one of 16 text boxes.
My question is this: Is it possible to have each text box to have a "default" number that gets put into a text box when it is empty.
This is needed to be done for all of the text boxes, so either a loop or a non specific code slice would be preferred.

Answer 1

The short answer is no.
The long answer is yes, you can.
Create your own textbox that inherits from the TextBox class, adding a property called "DefaultValue" Override the appropriate property/method adding logic for the default value.
Then simply replace the standard textbox with your textbox.
I hope you are validating the input as well because if TxtBoxWoodUnits.Text = "Foo" and you multiply it by 4.5, it's not gonna be pretty. You should turn on Error notifications for Implicit conversions as well, so you get compiler warnings when you try to multiply strings by numbers.
Public Class MyTextBox
Inherits TextBox
Public Property DefaultValue As String
Public Overrides Property Text As String
Get
If String.IsNullOrWhiteSpace(MyBase.Text) Then
Return DefaultValue
Else
Return MyBase.Text
End If
End Get
Set(ByVal value As String)
MyBase.Text = value
End Set
End Property
End Class

Answer 2

Well in the designer you could put the text value as "0", then in the textchanged event handler do this:
If TxtBoxWoodUnits.Text = "" Then
TxtBoxWoodUnits.Text = "0"
EndIf
Basically everytime the text of your textbox is changed, it checks if it is null, if it is, then make the value of textbox "0".
Hope this helps.

Answer 3

Private Sub btn_generate_text_array_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click ' will generate a group of 10 text boxes
Dim j As Integer
For j = 0 To 10
ReDim Preserve c(j)
c(j) = New TextBox
c(j).Name = "txt" & j
c(j).Parent = Me
c(j).Top = j * c(j).PreferredHeight + 2
c(j).Tag = j
c(j).Visible = True
Next
End Sub
Private Sub c_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
For j = 0 To 10 'loop will load 0 to all the text boxes having ""(null) values
If c(j).Text = "" Then
c(j).Text = "0"
End If
Next
End Sub