4个文本框中的值分配

Question

我的表单上有4个文本框和一个标签，4个文本框代表4种付款方式（现金，卡，银行转帐和其他付款方式）。 在我的标签中，我有汇总值，当我向收据中添加新项目时，该值会增加。

文本框名称为：cashTbox cardTbox bankTbox otherTbox 标签名称为：summaryLbl

默认情况下，cashTextbox.text等于summ.content，并且每次我向数据库添加项目时，我都会递增summaryLbl + itemPrice（数据库中的商品价格）。 我尝试过创建一个函数，该函数将允许我从cashTbox减去其他付款类型，而又不允许cashTbox变为负值。

我的代码如下：

 Private Sub cashTbox_LostKeyboardFocus(sender As Object, e As KeyboardFocusChangedEventArgs) Handles cashTbox.LostKeyboardFocus
    If sender.IsFocused = True And sender.text.length > 0 Then
        If calculateP(sender) = True Then

        End If
    End If
End Sub

Dim sumP as decimal = summaryLbl.content
Dim cashP as decimal = cashTbox.text
Dim cardP as decimal = cardTbox.text
Dim bankP as decimal = bankTbox.text
Dim otherP as decimal = otherTbox.text

Public Function calculateP(ByVal s As Object)
    Try
        If String.IsNullOrEmpty(s.text) Then
            s.text = "0,00"
        Else
            s.text = Decimal.Parse(s.text)
        End If
        If s Is cashTbox Then

        ElseIf s Is cardTbox Then
            cardP = s.text
            cashTbox.Text = sumP - (cardP + bankP + otherP )
        ElseIf s Is bankTbox Then
            bankP = s.text
            cashTbox.Text = sumP - (cardP + bankP + otherP )
        ElseIf s Is otherTbox Then
            otherP  = s.text
            cashTbox.Text = sumP - (cardP + bankP + otherP )
        End If
        cashTbox.Text = sumP - (cardP + bankP + otherP )
    Catch ex As Exception
    End Try
 setValues()
    Return True
End Function

Public Function setValues()
    summaryLbl.content = sumP
    cashTbox.text = cashP
    cardTbox.text = cardP
    bankTbox.text = bankP
    otherTbox.text = otherP
End Function