TextBox TextChanged错误

Question

我的代码需要做一些工作

Public Class Form1
Dim Bread, TotalPrice As Double
Private Sub txtBread_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles txtBread.TextChanged

    If txtBread.Text = "" Then
        TotalPrice = TotalPrice - Bread
        lblBread.Text = Bread.ToString
        lblPrice.Text = TotalPrice.ToString
    Else
        Bread = Val(txtBread.Text) * 3.25
        lblBread.Text = Bread.ToString
        TotalPrice = TotalPrice + Bread
        lblPrice.Text = TotalPrice.ToString
    End If


End Sub
End Class

我的文本框只适用于一位数字。所以我这里的错误是，当我在文本框中输入两位数字时，它实际上更新了我的标签，但当我按backspace时，它不再更新。

Answer 1

变量TotalPrice的值随着每个新输入(不管它是大于还是小于前一个)以及lblPrice.Text的值而增长。例如：

txtBread.Text    TotalPrice     
   1                  1
   15                 16
   1                  17

如果你确切地解释你想要完成什么，我可以更新你的代码。

Dim Bread As Double
Dim TotalPrice as Double = 5 'Any constant value you want
Private Sub txtBread_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles txtBread.TextChanged

    If txtBread.Text = "" Then
        lblBread.Text = Bread.ToString
        lblPrice.Text = Convert.ToString(TotalPrice - Bread)
    Else
        Bread = Val(txtBread.Text) * 3.25
        lblBread.Text = Bread.ToString
        lblPrice.Text = Convert.ToString(TotalPrice + Bread)
    End If
End Sub

Answer 2

试着用我的样本..

Public Class Form1
    Dim Bread As Double
    Dim TotalPrice As Double = 100 '---> maybe this is a result from a function

    Private Sub txtBread_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles txtBread.TextChanged

        If txtBread.Text = "" Then
            Bread = 0
        Else
            Bread = Val(txtBread.Text) * 3.25
        End If
        lblBread.Text = Bread.ToString
        lblPrice.Text = (TotalPrice + Bread).ToString
    End Sub
End Class