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The remainder of this article walks you through a demonstration program that shows just how easy it is to implement a useful MDI program by using the .NET Framework’s tools. The application is a text editor that permits you to have multiple documents open. It’s rather basic, implementing a bare minimum of commands including cut, copy, and paste. Here are the steps to follow:

  1. Create a new Visual Basic Windows application.
  2. With the initial form, change the IsMdiContainer property to True and the Text property to MDI Parent.
  3. Add a new Windows form to the project, specifying Document as the form name.
  4. Add a RichTextBox to the document form, and set its Dock property to Fill.
  5. Add a MenuStrip control to the parent form, and add File, Edit, and Window menu items to the MenuStrip.
  6. Set the MenuStrip’s MdiWindowListItem property to the Window menu item.
  7. Add New, Open, Save, Close, and Exit subitems to the File menu.
  8. Add Cut, Copy, and Paste subitems to the Edit menu.
  9. Add Tile Horizontally, Tile Vertically, and Cascade subitems to the Window menu.
  10. Add an OpenFileDialog control and a SaveFileDialog control to the parent form.

The next step is to add the code. Most of the code goes in the parent form; Listing 1 shows this code. Listing 2 shows the small amount of code for the document form. (The source.zip file contains all of the code to make it easier to use.)

Listing 1 Code in the text editor’s parent form.

Imports System.IO
Public Class Form1

’ Keep count of new documents created.
Private NewChildCount As Integer = 0

’ These event procedures deal with opening, saving, creating,
’ and closing documents.

Private Sub SaveToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles SaveToolStripMenuItem.Click
  Dim currentDoc As Document = Me.ActiveMdiChild
  If Not currentDoc Is Nothing Then
    If currentDoc.isNamed Then
      SaveDocument(currentDoc, currentDoc.Text)
      ’ No name assigned yet.
      SaveFileDialog1.Filter = "Text files *.txt | *.txt"
        SaveFileDialog1.FileName = currentDoc.Text & ".txt"
        If SaveFileDialog1.ShowDialog() = Windows.Forms.DialogResult.OK Then
          SaveDocument(currentDoc, SaveFileDialog1.FileName)
        End If
      End If
    End If
  End Sub

  Private Sub OpenToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles OpenToolStripMenuItem.Click
    ’ File, Open menu command.
    Dim sr As StreamReader
    OpenFileDialog1.FileName = ""
    OpenFileDialog1.Filter = "Text Files *.txt | *.txt"
    If OpenFileDialog1.ShowDialog = Windows.Forms.DialogResult.OK Then
        sr = File.OpenText(OpenFileDialog1.FileName)
        Dim newDoc As New Document()
        newDoc.RichTextBox1.Text = sr.ReadToEnd
        newDoc.Text = OpenFileDialog1.FileName
        newDoc.MdiParent = Me
        newDoc.isNamed = True
        ’ Move cursor to the start of the document.
        With newDoc.RichTextBox1
          .SelectionStart = 0
          .SelectionLength = 0
        End With
      Catch ex As Exception
        MsgBox("There was an error opening the file.")
      End Try
    End If

  End Sub

  Private Sub NewToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles NewToolStripMenuItem.Click
    ’ File, New command
    NewChildCount += 1
    Dim NewChild As New Document()
    NewChild.MdiParent = Me
    NewChild.Text = "Document " & NewChildCount.ToString
  End Sub

  Private Sub CloseToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CloseToolStripMenuItem.Click
    Dim ad As Document = Me.ActiveMdiChild
    If Not ad Is Nothing Then
    End If

  End Sub

  Private Sub ExitToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ExitToolStripMenuItem.Click
  End Sub

  ’These event procedures deal with arranging child windows.

  Private Sub TileHorizontallyToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TileHorizontallyToolStripMenuItem.Click
  End Sub

  Private Sub TileVerticallyTileToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TileVerticallyTileToolStripMenuItem.Click
  End Sub

  Private Sub CascadeToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CascadeToolStripMenuItem.Click
  End Sub

  ’ These event procedures are for cut, copy, and paste.

  Private Sub CutToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CutToolStripMenuItem.Click
    Dim ad As Document = Me.ActiveMdiChild
    If Not ad Is Nothing Then
      If ad.RichTextBox1.SelectionLength > 0 Then
        ad.RichTextBox1.SelectedText = ""
      End If
    End If
  End Sub

  Private Sub CopyToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CopyToolStripMenuItem.Click
    Dim ad As Document = Me.ActiveMdiChild
    If Not ad Is Nothing Then
      If ad.RichTextBox1.SelectionLength > 0 Then
      End If
    End If
  End Sub

  Private Sub PasteToolStripMenuItem_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles PasteToolStripMenuItem.Click
    Dim ad As Document = Me.ActiveMdiChild
    If Not ad Is Nothing Then
      Dim data As IDataObject = Clipboard.GetDataObject()
      If (data.GetDataPresent(DataFormats.Text)) Then
        ad.RichTextBox1.SelectedText = data.GetData(DataFormats.Text).ToString()
      End If
    End If
  End Sub

  ’ This sub is called to save a document.

  Private Sub SaveDocument(ByVal doc As Document, ByVal FileName As String)
      Dim sw As New StreamWriter(FileName)
      doc.isNamed = True
      doc.isDirty = False
    Catch ex As Exception
      MsgBox("There was an error saving the file.")
    End Try
  End Sub

End Class

Listing 2 Code in the text editor’s child form.

Public Class Document

  ’ True if the document has a name other than the default one.
  Public isNamed As Boolean = False
  ’ True if the document content has changed since opening/saving.
  Public isDirty As Boolean = False

  Private Sub RichTextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles RichTextBox1.TextChanged
    ’ Mark the document as dirty.
    isDirty = True
  End Sub

End Class

Figure 1 shows the application in action.

Figure 1

Figure 1 The text editor in action.

If you want to take this application further, you will probably want to add a few more basics:

  • Define the standard shortcut keys, such as Ctrl+C for Edit > Copy and Ctrl+N for File > New.
  • Add a File > Save As command.
  • Add code to prevent the accidental closing of unsaved documents.
  • Permit the user to specify the font used for document display.
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