不能从VB类中获得价值

Question

我试图在Visual Basic中创建一个简单的，基于类的计算器，但是当我按下按钮（加）（乘）时，它在文本框中显示为0。

这是我的代码：  表格2：

Public Class Form2
Dim Class2 As part2Class = New part2Class()
Dim Class2b As part2ClassB = New part2ClassB()
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Dim Num1 As Integer = CType(TextBox1.Text, Integer)
    Dim Num2 As Integer = CType(TextBox2.Text, Integer)
    MessageBox.Show(Class2.Calculate().ToString())
End Sub

Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
    Dim Num1 As Integer = CType(TextBox1.Text, Integer)
    Dim Num2 As Integer = CType(TextBox2.Text, Integer)
    MessageBox.Show(Class2b.Calculate())
End Sub

结束班级

---

part2Class CLASS

Public Class part2Class

    Public Property Num1
    Public Property Num2

    Public Overridable Function Calculate() As Integer
        Return Num1 + Num2

    End Function
End Class

---

Part2ClassB

Public Class part2ClassB
    Inherits part2Class
    Public Overrides Function Calculate() As Integer
        Return Num1 * Num2
    End Function
End Class

当我在文本框中输入值并按ADD / MULIPLY时，该值将显示为0。

Answer 1

您没有将值分配给类的属性。试试这个：

Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
    Dim Num1 As Integer = CType(TextBox1.Text, Integer)
    Dim Num2 As Integer = CType(TextBox2.Text, Integer)

    Class2b.Num1=Num1
    Class2b.Num2=Num2
    MessageBox.Show(Class2b.Calculate())
End Sub

Answer 2

如果CType失败，您将使程序崩溃。我将其更改为TryParse，该变量在第二个参数（在本例中为类的属性）中设置变量，并返回True或False。 AndAlso一到达False就停止，并前进到Else

的If部分

您需要在类中使用数据类型声明属性。查看我对Option Strict的评论。

Public Class part2Class

    Public Property Num1 As Integer
    Public Property Num2 As Integer

    Public Overridable Function Calculate() As Integer
        Return Num1 + Num2
    End Function
End Class


Public Class part2ClassB
    Inherits part2Class
    Public Overrides Function Calculate() As Integer
        Return Num1 * Num2
    End Function
End Class

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Dim Class2 As part2Class = New part2Class()
        Dim message As String
        If Integer.TryParse(TextBox1.Text, Class2.Num1) AndAlso Integer.TryParse(TextBox2.Text, Class2.Num2) Then
            message = Class2.Calculate().ToString
        Else
            message = "Please enter a number in both text boxes."
        End If
        MessageBox.Show(message)
End Sub

Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
    Dim Class2b As part2ClassB = New part2ClassB()
    Dim message As String
    If Integer.TryParse(TextBox1.Text, Class2b.Num1) AndAlso Integer.TryParse(TextBox2.Text, Class2b.Num2) Then
        message = Class2b.Calculate().ToString
    Else
        message = "Please enter a number in both text boxes."
    End If
    MessageBox.Show(message)
End Sub