Question

大家好我有这个程序，我想将form1的文本显示到我的form3，其中form2有执行命令的按钮，调试中没有错误但是当我点击我的form2中的按钮时我希望我的form3上的form3上的数据不存在。请提前帮助我们。

Form1代码：

 Public Class Form1
Private frm2 As Form2
Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click

    If frm2 Is Nothing Then
        frm2 = New Form2
        AddHandler frm2.FormClosed, AddressOf Me.Form2HasBeenClosed

        Dim Label21 As Label = New Label
        frm2.Label21.Text = TextBox1.Text
        frm2.Label21.ForeColor = Color.Black
     End If

    If frm2 IsNot Nothing Then
        frm2.Show(Me) 'Show Second Form  
        Me.Hide()
    End If

End Sub

Form2代码：

Public Class Form2
Private frm1 As New Form1
Private frm3 As Form3
Public lbl As New Label
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click


    Dim Label21 As Label = New Label
    Dim Textbox1 As TextBox = New TextBox
    frm3.Label21.Text = frm1.TextBox1.Text

        Form3.Show()


End Sub
End Class

Answer 1

您需要将Form1实例的引用传递给名为frm2的Form2实例当您在Form2类代码中尝试显示Form3时，您应该使用该引用来传递Form1的初始实例中存在的值。而是您的代码构建Form1的新实例（Form1 frm = new Form1）并尝试从此实例获取值。当然，作为Form1的新实例，frm1变量不包含原始实例中存在的任何值。

Public Class Form2
    Private frm1 As Form1   ' remove the new here because it creates a new instance of Form1'
    Private frm3 As Form3
    Public lbl As New Label ' not needed?'

    ' add a constructor that receives the instance of the caller'
    Public Sub New(callerInstance as Form1)

        ' Call required if you add your constructor manually'
        InitializeComponent()

        ' save the instance of the Me variable passed to this constructor'
        frm1 = callerInstance
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

       ' Dim Label21 As Label = New Label          ' this label is not needed'
       ' Dim Textbox1 As TextBox = New TextBox     ' this  textbox is not needed'

       ' Create a new instance of Form3, do not use the automatic Form3 instance
       ' automatically created by VB.NET 
       frm3 = new Form3()

       ' now you are referring to the caller instance of Form1 '
       ' where there is the textbox filled with your text '
       frm3.Label21.Text = frm1.TextBox1.Text
       frm3.Show()

     End Sub
End Class

然后更改以这种方式构建Form2实例的Fomr1类中的代码

Private Sub Button3_Click(...........)

    If frm2 Is Nothing Then
        frm2 = New Form2(Me)
        .....

此更改使用Form1（Me）的当前实例调用Form2的类代码中定义的构造函数，并且此实例包含您稍后需要传递给frm3的文本框值。

我不想在这里光顾，但似乎你对类的类和实例有点混淆。您需要非常好地理解这一点，因为它是面向对象编程的基本支柱之一。（VB自动创建Form对象在这里没有帮助）

这里有一个非常基本的介绍：Classes and Objects

奇怪的VB.net显示其他表单行为的文本

1 个答案: