在子表單中發送資料-有解無憂

我有 3 個表單，分別是 MainForm、Form1 和 Form2。MainForm 在Panel. 在單擊buttonMainForm 中的a時，我正在使用ShowDialog()方法打開 Form2 。現在我有一個treeviewin Form2. 現在我想將在 Form2 中選擇的節點傳遞回comboboxForm1 中的 a。如何做到這一點？我Form1.Activate()在 Form2 中嘗試過，但代碼沒有Activate在 Form1 中命中方法。

我也在使用，Form1.ComboBox1.Items.Add(Me.TreeView1.SelectedNode.Text)但一旦 Form2 關閉，我就看不到 ComboBox 中的任何專案。我在這里缺少什么？

下面是代碼以便更好地理解。

MainForm

public Class MainForm

   private Sub OpenChildForm(childForm As Form)
       panelFormContainer.Controls.Add(childForm)
       childForm.Dock = DockStyle.Fill
       childForm.Show()
   End Sub  
   
   private sub MainForm_OnLoad(sender As Object, e as EventArgs) Handles Me.Load
      
      'Adding child form to a Panel in Main Form
      OpenChildForm(new Form1())
   End Sub

   'Open Form 2 on Button Click
   private sub btnOpenForm3_Click(sender As Object, e as EventArgs) Handles btnOpenForm3.Click
       Form2.ShowDialog()
   End Sub 
End Class

Form2 - Child Form Opened by button click in MainForm

Public Class Form2

   'Click back button to go back to Main Form which is already having Form1 as child
   Private Sub btnBack_Click(sender As Object, e As EventArgs)
      Me.Close()
      Form1.Activate()
   End Sub

   'Click a Button to Add Selected Treeview node to Combo in Form1 
   Private Sub btnAdd_Click(sender As Object, e As EventArgs) btnAdd.Click
      Form1.ComboBox1.Items.Add(Me.TreeView1.SelectedNode.Text)
   End Sub

End Class

更新：我已經更新了代碼，但仍然沒有在 Child Form1 的 ComboBox 中得到任何東西

MainForm

Public Class Form1

Private currentChildForm As Form = Nothing
Private ownerForm As Form = Nothing
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    OpenChildForm(New ChildForm1())

End Sub

Private Sub OpenChildForm(childForm As Form)
    If currentChildForm IsNot Nothing Then
        currentChildForm.Close()
    End If

    childForm.TopLevel = False
    childForm.FormBorderStyle = FormBorderStyle.None
    panelFormContainer.Controls.Clear()

    panelFormContainer.Controls.Add(childForm)

    childForm.Dock = DockStyle.Fill

    childForm.BringToFront()
    childForm.Show()

End Sub

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Dim dialogForm As ChildForm2 = New ChildForm2()
    '
    Dim result = dialogForm.ShowDialog()
    If result = DialogResult.OK Then
        AddHandler ChildForm2.Button1.Click, AddressOf ChildForm1.objForm2_Passvalue
    End If
End Sub


End Class

ChildForm1 which is hosted in MainForm

Public Class ChildForm1
    Private Sub ChildForm1_Load(sender As Object, e As EventArgs) Handles MyBase.Load

    If ComboBox1.Items.Count > 0 Then
        ComboBox1.SelectedIndex = 0
    End If
End Sub

Private Sub ChildForm1_Activated(sender As Object, e As EventArgs) Handles Me.Activated

End Sub

Public Sub objForm2_Passvalue(sender As Object, e As EventArgs)
    Me.ComboBox1.Items.Add(PageDetail.PageTitle)
End Sub

End Class

ChildForm2 -- Which is opened as Dialog

Public Class ChildForm2

Private Sub ChildForm2_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    TreeView1.ExpandAll()
    Button1.DialogResult = DialogResult.OK
End Sub

Public Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    PageDetail.PageTitle = TreeView1.SelectedNode.Text
    Me.Close()
End Sub

Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
    Me.Close()
End Sub
End Class

PageDetail: Class used to get and set data

Public NotInheritable Class PageDetail

    Private Shared pageTitleValue As String

    Public Shared Property PageTitle As String
        Get
            Return pageTitleValue
        End Get
        Set(value As String)
            pageTitleValue = value
        End Set
    End Property

End Class

在子表單中發送資料

uj5u.com熱心網友回復：

與其將 aForm放在面板上，不如考慮創建 aUserControl并將其放置在面板上。下面顯示了如何將資料從顯示的 Form (Form2) 傳遞ShowDialog()到存在于不同表單 (MainForm) 上的 UserControl (UserControl1)。

注：MainForm是啟動形式。如果需要，可以將 UserControl 替換為 Form。

創建一個新專案

VS 2019：

在 VS 選單中，單擊檔案
選擇新建
選擇專案
選擇Windows 表單應用程式 (.NET Framework)
單擊下一步
輸入所需的專案名稱
點擊創建

打開解決方案資源管理器

在 VS 選單中，選擇查看
選擇解決方案資源管理器

添加用戶控制元件（名稱：UserControl1.vb）

在解決方案資源管理器中，右鍵單擊 <專案名稱>，選擇添加
選擇用戶控制元件（Windows 表單）...（名稱：UserControl1.vb）
添加一個Label（文本：“選擇一個”）
添加一個ComboBox（名稱：ComboBox1）

用戶控制元件1.vb

Public Class UserControl1

    Private Sub UserControl1_Load(sender As Object, e As EventArgs) Handles MyBase.Load

    End Sub

    Public Sub PopulateComboBox(value As String)
        'remove existing data from ComboBox
        ComboBox1.Items.Clear()
        ComboBox1.Text = String.Empty

        'add 
        ComboBox1.Items.Add(value)

        If ComboBox1.Items.Count = 1 Then
            'if only 1 item exists, select it
            ComboBox1.SelectedIndex = 0
        End If
    End Sub
End Class

注意：如果使用 aForm而不是 a UserControl，請將 for 代碼添加PopulateComboBox到您的表單中。

添加表單（名稱：Form2.vb）

在解決方案資源管理器中，右鍵單擊 <專案名稱>，選擇添加
選擇表單（Windows 表單）...（名稱：Form2.vb）
添加標簽
添加一個TreeView（名稱：TreeView1）
添加按鈕（名稱：btnAdd；文本：添加）
Double-click "btnAdd" to add the Click event handler
Add a Button (Name: btnCancel; Text: Cancel)
Double-click "btnCancel" to add the Click event handler

In Solution Explorer, right click Form2.vb, and select View Code

Form2.vb

Imports System.IO
Public Class Form2

    Private Sub Form2_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        PopulateTreeView()
    End Sub

    'ToDo: Replace this function with one that returns the desired data
    Public Function GetSelectedValue() As String
        Return TreeView1.SelectedNode.Text
    End Function

    Private Sub PopulateTreeView()

        'ToDo: Replace this code with your desired code to populate the TreeView

        'clear
        TreeView1.Nodes.Clear()

        Dim topNode As TreeNode = New TreeNode("Computer")

        TreeView1.Nodes.Add(topNode)

        Dim logicalDrives As String() = Directory.GetLogicalDrives()

        If logicalDrives IsNot Nothing Then
            For Each drive As String In logicalDrives
                Debug.WriteLine("drive: " & drive.ToString())

                Try
                    Dim dirInfo As DirectoryInfo = New DirectoryInfo(drive)

                    TreeView1.Nodes.Add(New TreeNode(drive))

                Catch ex As Exception
                    'do nothing
                End Try
            Next
        End If
    End Sub

    Private Sub btnAdd_Click(sender As Object, e As EventArgs) Handles btnAdd.Click
        'in MainForm we'll subscribe to the Add button Click event and retrieve the data by calling function "GetSelectedValue", so all we have to do here is close the form
        Me.Close()
    End Sub

    Private Sub btnCancel_Click(sender As Object, e As EventArgs) Handles btnCancel.Click
        Me.Close()
    End Sub
End Class

Rename Form1 to MainForm

In Solution Explorer, right-click Form1.vb
Select Rename
Enter MainForm.vb
When prompted "You are renaming a file. Would you also like to perform a rename in this project of all references to the code element 'Form1'? Click Yes
In Properties Window, for "MainForm", set Text = "MainForm"

Build Project

In Solution Explorer, right-click <project name>, select Build

MainForm

Add a panel to MainForm (Name: panel1)
In Toolbox (View => Toolbox), expand: <solution name> Components
Drag UserControl1 onto panel1 on MainForm
Add Button (Name: btnOpenForm2; Text: Open Form2)
Double-click "btnOpenForm2" to add the Click event handler

In Solution Explorer, right click MainForm.vb, and select View Code

MainForm.vb

Public Class MainForm

    Private frm2 As Form2 = Nothing

    Private Sub MainForm_Load(sender As Object, e As EventArgs) Handles MyBase.Load

    End Sub

    Private Sub btnOpenForm2_Click(sender As Object, e As EventArgs) Handles btnOpenForm2.Click
        If frm2 Is Nothing Then
            'create new instance
            frm2 = New Form2()
        End If

        'subscribe to events (add event handlers)
        AddHandler frm2.btnAdd.Click, AddressOf Frm2BtnAdd_Click

        'show dialog 
        frm2.ShowDialog()

        'the code below will execute after frm2 is closed

        'unsubscribe from events (remove event handlers)
        RemoveHandler frm2.btnAdd.Click, AddressOf Frm2BtnAdd_Click

        'dispose
        frm2.Dispose()

        frm2 = Nothing
    End Sub

    Private Sub Frm2BtnAdd_Click(sender As Object, e As System.EventArgs)

        'call method to populate ComboBox
        'UserControl11.PopulateComboBox(frm2.GetSelectedValue())

        'call function to get data
        Dim userSelection As String = frm2.GetSelectedValue()

        'call method to populate ComboBox
        UserControl11.PopulateComboBox(userSelection)

    End Sub
End Class

Here's a demonstration:

在子表單中發送資料

Resources

注：MainForm為啟動表單，是父母雙方ChildForm1和ChildForm2（即：兩個實體ChildForm1，并ChildForm2在創建的MainForm）

創建一個新專案

VS 2019：

在 VS 選單中，單擊檔案
選擇新建
選擇專案
選擇Windows 表單應用程式 (.NET Framework)

在子表單中發送資料

單擊下一步
輸入所需的專案名稱
點擊創建

打開解決方案資源管理器

在 VS 選單中，選擇查看
選擇解決方案資源管理器

添加表單（名稱：ChildForm1.vb）

在解決方案資源管理器中，右鍵單擊 <專案名稱>，選擇添加
選擇表單（Windows 表單）...（名稱：ChildForm1.vb）
添加一個Label（文本：“選擇一個”）
添加一個ComboBox（名稱：ComboBox1）

在子表單中發送資料

在解決方案資源管理器中，右鍵單擊ChildForm1.vb，然后選擇查看代碼

子表單1.vb

Public Class ChildForm1

    Public WriteOnly Property PageTitle As String
        Set(value As String)
            'populate ComboBox
            PopulateComboBox(value)
        End Set
    End Property

    Sub New()

        ' This call is required by the designer.
        InitializeComponent()

        ' Add any initialization after the InitializeComponent() call.

    End Sub

    Sub New(pageTitle As String)

        ' This call is required by the designer.
        InitializeComponent()

        ' Add any initialization after the InitializeComponent() call.
        PopulateComboBox(pageTitle)

    End Sub

    Sub New(pageTitles As List(Of String))

        ' This call is required by the designer.
        InitializeComponent()

        ' Add any initialization after the InitializeComponent() call.
        PopulateComboBox(pageTitles)

    End Sub

    Private Sub ChildForm1_Load(sender As Object, e As EventArgs) Handles MyBase.Load

    End Sub

    Public Sub PopulateComboBox(pageTitle As String)
        'create new instance
        Dim pageTitles As New List(Of String)

        'add
        pageTitles.Add(pageTitle)

        'populate ComboBox
        PopulateComboBox(pageTitles)
    End Sub

    Public Sub PopulateComboBox(pageTitles As List(Of String))
        'remove existing data from ComboBox
        ComboBox1.Items.Clear()
        ComboBox1.Text = String.Empty

        For Each pTitle In pageTitles
            'add 
            ComboBox1.Items.Add(pTitle)
        Next

        If ComboBox1.Items.Count = 1 Then
            'if only 1 item exists, select it
            ComboBox1.SelectedIndex = 0
        End If
    End Sub
End Class

添加表單（名稱：ChildForm2.vb）

在解決方案資源管理器中，右鍵單擊 <專案名稱>，選擇添加
Select Form (Windows Forms)... (Name: ChildForm2.vb)
Add a Label
Add a TreeView (name: TreeView1)
Add a Button (Name: btnAdd; Text: Add)
Double-click "btnAdd" to add the Click event handler
Add a Button (Name: btnCancel; Text: Cancel)
Double-click "btnCancel" to add the Click event handler

在子表單中發送資料

In Solution Explorer, right click ChildForm2.vb, and select View Code

ChildForm2.vb

Public Delegate Sub PassValueHandler(ByVal strValue As String)

Public Class ChildForm2

    Public Event PassValue As PassValueHandler

    Public ReadOnly Property PageTitle
        Get
            Return TreeView1.SelectedNode.Text
        End Get
    End Property

    Private Sub Form2_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        PopulateTreeView()
        TreeView1.ExpandAll()
    End Sub

    Public Function GetPageTitle() As String
        Return PageTitle
    End Function

    Private Sub PopulateTreeView()
        'ToDo: Replace this method with code to populate your TreeView

        TreeView1.Nodes.Clear()

        'Parent 1
        Dim node1 As TreeNode = New TreeNode("Parent 1")
        Dim childNode1 As TreeNode = New TreeNode("Child Node 1")

        'add 
        node1.Nodes.Add(childNode1)

        'add 
        TreeView1.Nodes.Add(node1)

        'Parent 2
        Dim node2 As TreeNode = New TreeNode("Parent 2")
        Dim childNode2 As TreeNode = New TreeNode("Child Node 2")

        'add 
        node2.Nodes.Add(childNode2)

        'add 
        TreeView1.Nodes.Add(node2)

    End Sub

    Private Sub btnAdd_Click(sender As Object, e As EventArgs) Handles btnAdd.Click
        'raise event
        RaiseEvent PassValue(TreeView1.SelectedNode.Text)

        'set value
        Me.DialogResult = DialogResult.OK

        'close
        Me.Close()

    End Sub

    Private Sub btnCancel_Click(sender As Object, e As EventArgs) Handles btnCancel.Click
        'set value
        Me.DialogResult = DialogResult.Cancel

        'close
        Me.Close()
    End Sub
End Class

Rename Form1 to MainForm

In Solution Explorer, right-click Form1.vb
Select Rename
Enter MainForm.vb
When prompted "You are renaming a file. Would you also like to perform a rename in this project of all references to the code element 'Form1'? Click Yes
In Properties Window, for "MainForm", set Text = "MainForm"

MainForm

Add a panel to MainForm (Name: panelFormContainer)
Add Button (Name: btnOpenChildForm2; Text: Open ChildForm2)
Double-click "btnOpenChildForm2" to add the Click event handler

在子表單中發送資料

In Solution Explorer, right click MainForm.vb, and select View Code

In the code below, I've written it in such a way that it allows one to choose different options for both retrieving data from a child form, as well as, multiple options for sending data to a child form.

MainForm.vb

Public Class MainForm

    Private dialogForm As ChildForm2 = Nothing
    Private currentChildForm As Form = Nothing
    Private ownerForm As Form = Nothing

    Private Sub MainForm_Load(sender As Object, e As EventArgs) Handles MyBase.Load

        'open Form
        OpenChildForm(New ChildForm1())
    End Sub

    Private Sub OpenChildForm(ByRef childForm As Form)
        If currentChildForm IsNot Nothing Then
            currentChildForm.Dispose()
            currentChildForm = Nothing
        End If

        'set value
        currentChildForm = childForm

        'set properties
        childForm.Dock = DockStyle.Fill
        childForm.TopLevel = False
        childForm.FormBorderStyle = FormBorderStyle.None

        'remove existing controls
        panelFormContainer.Controls.Clear()

        'add
        panelFormContainer.Controls.Add(childForm)

        'show
        childForm.Show()

    End Sub

    Private Sub PopulateChildForm1ComboBox(pageTitle As String)
        If currentChildForm.GetType() = ChildForm1.GetType() Then
            'currentChildForm is an instance of ChildForm1

            'create reference
            Dim frm = CType(currentChildForm, ChildForm1)

            'option 1 - populate ComboBox by calling method
            frm.PopulateComboBox(pageTitle)

            'option 2 - populate ComboBox by setting property
            'frm.PageTitle = PageDetail.PageTitle
        End If
    End Sub

    Private Sub btnOpenChildForm2_Click(sender As Object, e As EventArgs) Handles btnOpenChildForm2.Click
        'ToDo: Replace this method with code from Option 1, Option 2, or Option 3 below
                           ...

    End Sub

    Private Sub DialogForm_BtnAdd_Click(sender As Object, e As System.EventArgs)

        'option 1 - get page title from property
        PageDetail.PageTitle = dialogForm.PageTitle

        'option 2 - get page title by calling function
        'PageDetail.PageTitle = dialogForm.GetPageTitle()

        'populate ComboBox
        PopulateChildForm1ComboBox(PageDetail.PageTitle)
    End Sub

    Private Sub DialogForm_PassValue(e As String)
        'set value
        PageDetail.PageTitle = e

        'populate ComboBox
        PopulateChildForm1ComboBox(e)
    End Sub
End Class

Choose one of the following options for retrieving data from ChildForm2. Replace the method btnOpenChildForm2_Click (in MainForm.vb) with the code listed below.

Option 1 (DialogResult.OK)

Private Sub btnOpenChildForm2_Click(sender As Object, e As EventArgs) Handles btnOpenChildForm2.Click
    'create new instance
    dialogForm = New ChildForm2()

    'show dialog
    If dialogForm.ShowDialog() = DialogResult.OK Then
        PageDetail.PageTitle = dialogForm.PageTitle

        'populate ComboBox
        PopulateChildForm1ComboBox(PageDetail.PageTitle)
    End If

    'dispose
    dialogForm.Dispose()

    dialogForm = Nothing
End Sub

Note: When using Option 1, the code for DialogForm_BtnAdd_Click and DialogForm_PassValue (in MainForm.vb) isn't used, so both of these methods can be removed.

Option 2 (subscribe to btnAdd 'Click' event)

Private Sub btnOpenChildForm2_Click(sender As Object, e As EventArgs) Handles btnOpenChildForm2.Click
    'create new instance
    dialogForm = New ChildForm2()

    'subscribe to events (add event handlers)
    AddHandler dialogForm.btnAdd.Click, AddressOf DialogForm_BtnAdd_Click

    'show dialog
    dialogForm.ShowDialog()

    'unsubscribe from events (remove event handlers)
    RemoveHandler dialogForm.btnAdd.Click, AddressOf DialogForm_BtnAdd_Click

    'dispose
    dialogForm.Dispose()

    dialogForm = Nothing
End Sub

Note: When using Option 2, the code for DialogForm_PassValue (in MainForm.vb) isn't used, so method DialogForm_PassValue can be removed.

Option 3 (subscribe to event 'PassValue')

Private Sub btnOpenChildForm2_Click(sender As Object, e As EventArgs) Handles btnOpenChildForm2.Click
    'create new instance
    dialogForm = New ChildForm2()

    'subscribe to events (add event handlers)
    AddHandler dialogForm.PassValue, AddressOf DialogForm_PassValue

    'show dialog
    dialogForm.ShowDialog()

    'unsubscribe from events (remove event handlers)
    RemoveHandler dialogForm.PassValue, AddressOf DialogForm_PassValue

    'dispose
    dialogForm.Dispose()

    dialogForm = Nothing
End Sub

Note: When using Option 3, the code for DialogForm_BtnAdd_Click (in MainForm.vb) isn't used, so method DialogForm_BtnAdd_Click can be removed.

Here's a demo:

在子表單中發送資料

Resources:

Form.ShowDialog
Form.Show
How to populate a treeview from a list of objects

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