Send data within Child Forms

Question

I have 3 Forms namely MainForm, Form1 and Form2. MainForm hosts Form1 in a Panel. On Clicking a button in MainForm, I am opening Form2 using ShowDialog() method. Now I have a treeview in Form2. Now I want to pass the nodes selected in Form2 back to a combobox in Form1. How can this be achieved? I have tried Form1.Activate() in Form2 but the code is not hitting Activate method in Form1.

Also I am using Form1.ComboBox1.Items.Add(Me.TreeView1.SelectedNode.Text) but I cannot see any items in ComboBox once Form2 is closed. What am I missing here?

Below is the code for better understanding.

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

Updated: I have updated the code but still not getting anything in ComboBox of Child Form1

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

It all makes cents · Accepted Answer

The following shows multiple ways to pass data between forms. In the code below, I show how to retrieve data from a child form (ChildForm2) using a function, a property, or an event. This data is passed back to the parent form (MainForm). Once the parent form (MainForm) receives the data, it sends the data to a different child form (ChildForm1). Data can be sent from the parent form (MainForm) to the child form (ChildForm1) using one of the constructors, a method, or a property.

Note: MainForm is the startup form and is the parent to both ChildForm1 and ChildForm2 (ie: instances of both ChildForm1 and ChildForm2 are created in MainForm)

Create a new project

VS 2019:

In VS menu, click File
Select New
Select Project
Select Windows Forms App (.NET Framework)

Click Next
Enter desired project name
Click Create

Open Solution Explorer

In VS menu, select View
Select Solution Explorer

Add Form (Name: ChildForm1.vb)

In Solution Explorer, right-click , select Add
Select Form (Windows Forms)... (name: ChildForm1.vb)
Add a Label (Text: "Select One")
Add a ComboBox (Name: ComboBox1)

In Solution Explorer, right click ChildForm1.vb, and select View Code

ChildForm1.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

Add a Form (name: ChildForm2.vb)

In Solution Explorer, right-click , select Add
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

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

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:

Resources:

Send data within Child Forms

Answers (2)

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