How to Pass Data Across Forms

In this post we will discuss how can we share different variables among Forms.

Level: Beginner

Knowledge Required:
Win Forms

Description:
While creating a Windows Forms Application, we usually face a requirement when we need to pass one or more variables from one Form to another. For example, we have created a Dialog Box which takes Date Range,

When we display this dialog box, we want that a default date range should be given, also this dialog box should return the new Date Range that is selected.

To pass the data to Form we can directly use Form's Control as,

In Form1.Button1.Click Event Handler:

DateRangeDialog.DateTimePicker1.Value = Now

As you can see the above code, I have used the DateRangeDialog's DateTimePicker control in Form1's Button Click event Handler, but it is better to create Public Properties on Form and use them. Also we can utilize the Constructor (New Method).

Public Class dlgDateRange
    Private _DateStart As Date
    Private _DateEnd As Date

    'Public properties that will be used to get the selected dates
    Public ReadOnly Property DateStart() As Date
        Get
            Return Me._DateStart
        End Get
    End Property

    Public ReadOnly Property DateEnd() As Date
        Get
            Return Me._DateEnd
        End Get
    End Property

    ' default constructor
    Public Sub New()
        ' This call is required by the Windows Form Designer.
        InitializeComponent()
        ' Add any initialization after the InitializeComponent() call.
        Me._DateStart = Now
        Me._DateEnd = Now
    End Sub

    ' if dates are supplied on initializing
    Public Sub New(ByVal DateStart As Date, ByVal DateEnd As Date)
        Me.New()
        ' Add any initialization after the InitializeComponent() call.
        Me._DateStart = DateStart
        Me._DateEnd = DateEnd
    End Sub

    ' OK button is clicked
    Private Sub OK_Button_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles OK_Button.Click
        ' set the selected values and close dialog
        Me._DateStart = Me.DateTimePicker1.Value
        Me._DateEnd = Me.DateTimePicker2.Value
        Me.DialogResult = System.Windows.Forms.DialogResult.OK
        Me.Close()
    End Sub
    
    ' cancel button is clicked
    Private Sub Cancel_Button_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Cancel_Button.Click
        Me.DialogResult = System.Windows.Forms.DialogResult.Cancel
        Me.Close()
    End Sub

    ' on form load event we will set the dates which were supplied on initializing
    Private Sub dlgDateRange_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Me.DateTimePicker1.Value = Me._DateStart
        Me.DateTimePicker2.Value = Me._DateEnd
    End Sub
End Class

Usage:

Dim dlgNew As dlgDateRange
dlgNew = New dlgDateRange(New Date(2008, 1, 1), New Date(2008, 6, 30))
If dlgNew.ShowDialog() = Windows.Forms.DialogResult.OK Then
    Debug.Print("Date Start: " & dlgNew.DateStart)
    Debug.Print("Date End: " & dlgNew.DateEnd)
End If