VB.NET MDI Form

MDI stands for Multiple Document Interface applications that allow users to work with multiple documents by opening more than one document at a time. Whereas, a Single Document Interface (SDI) application can manipulate only one document at a time.

The MDI applications act as the parent and child relationship in a form. A parent form is a container that contains child forms, while child forms can be multiple to display different modules in a parent form.

VB.NET has folowing rules for creating a form as an MDI form.

MidParent: The MidParent property is used to set a parent form to a child form.
ActiveMdiChild: The ActiveMdiChild property is used to get the reference of the current child form.
IsMdiContainer: The IsMdiContainer property set a Boolean value to True that represents the creation of a form as an MDI form.
LayoutMdi(): The LayoutMdi() method is used to arrange the child forms in the parent or main form.
Controls: It is used to get the reference of control from the child form.

Let's create a program to display the multiple windows in the VB.NET Windows Forms.

Step 1: First, we have to open the Windows form and create the Menu bar with the use of MenuStrip control, as shown below.

Step 2: After creating the Menu, add the Subitems into the Menu bar, as shown below.

In the above image, we have defined two Subitems, First is the Feedback Form, and the Second is VB.NET.

Step 3: In the third step, we will create two Forms: The Child Form of the Main Form or Parent Form.

Here, we have created the first Child Form with the name Form2.

Form2.vb

Public Class Form2
    Private Sub Form2_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Me.Text = "Feedback form" ' Set the title of the form
        Label1.Text = " Fill the Feedback form"
        Button1.Text = "Submit"
        Button1.BackColor = Color.SkyBlue
        Button2.Text = "Cancel"
        Button2.BackColor = Color.Red
    End Sub
    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        MsgBox(" Successfully submit the feedback form")
    End Sub
    Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
        Me.Dispose() ' end the form2
    End Sub
End Class

Another Child Form with the name Form3.

Form3.vb

Public Class Form3
    Private Sub Form3_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Label1.Text = "Welcome to JavaTpoint Tutorial Site"
        Label.BackColor = Color.Green
        Label2.Text = "This is the VB.NET Tutorial and we are learning the VB.NET MDI Form"
        Label2.BackColor = Color.SkyBlue
    End Sub
End Class

Step 4: Now we write the programming code for the Main or Parent Form, and here is the code for our Main Form.

MDI_form.vb

Public Class MDI_Form
    Private Sub MDI_Form_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        IsMdiContainer = True 'Set the Boolean value to true to create the form as an MDI form.
        Me.Text = "javatpoint.com" 'set the title of the form
        PictureBox1.Image = Image.FromFile("C:\Users\AMIT YADAV\Desktop\jtp2.png")
        PictureBox1.Height = 550
        PictureBox1.Width = 750
    End Sub
    Private Sub FeedbackFormToolStripMenuItem_Click(sender As Object, e As EventArgs) Handles FeedbackFormToolStripMenuItem.Click
        PictureBox1.Visible = False
        Dim fm2 As New Form2
        fm2.MdiParent = Me 'define the parent of form3, where Me represents the same form
        fm2.Show() 'Display the form3
    End Sub
    Private Sub VBNETToolStripMenuItem_Click(sender As Object, e As EventArgs) Handles VBNETToolStripMenuItem.Click
        PictureBox1.Visible = False
        Dim fm3 As New Form3
        fm3.MdiParent = Me 'define the parent of form3, where Me represent the same form
        fm3.Show() 'Display the form3
    End Sub
End Class

Output:

After that, click on the Menu button, it shows two sub-items of the Menu as Feedback Form and VB.NET. We have clicked on the Feedback Form that displays the following form on the window.