Focusing on Forms and Menus in Visual Basic - 4.18 Changing Menus at Runtime
(Page 4 of 5 )

Problem

You want to customize the menu structure in your main form at runtime. The structure should be based on settings made available by some user-configurable method.

Solution

Sample code folder: Chapter 04\RuntimeMenus

The menu-specific classes included in the Windows Forms library can be created at either design time or runtime. This recipe’s code adds a basic menu to a form at design time and enhances it at runtime by adding the user’s Internet Explorer “Favorites” to one of the menus.

Create a new Windows Forms application, and add aMenuStripcontrol namedMainMenuto the form. Perform the following actions on this menu:

1. Add a top-level menu namedMenuFile, using&Filefor itsTextproperty.
   
2. Add a top-level menu namedMenuFavorites, usingFa&voritesfor itsTextproperty.
   
3. Add a menu item namedMenuExitProgramthat is subordinate toMenuFile, usingE&xitfor itsTextproperty. Set itsShortcutKeysproperty toAlt+F4.
   
4. Add a menu item namedMenuNoFavoritesthat is subordinate toMenuFavorites, using(empty)for itsTextproperty. Set itsEnabledproperty toFalse.

Figure 4-19 shows a partial look at this form’s menu structure in design mode.

Figure 4-19.  The initial menus for the runtime menu sample

Next, replace the form’s code template with the following code. I’ve highlighted the lines that do the actual adding of menu items:

  Imports MVB = Microsoft.VisualBasic

  Public Class Form1
     Private Declare Auto Function GetPrivateProfileString_
        Lib "kernel32" _
        (ByVal AppName As String, _
        ByVal KeyName As String, _
        ByVal DefaultValue As String, _
        ByVal ReturnedString As System.Text.StringBuilder, _
        ByVal BufferSize As Integer, _
        ByVal FileName As String) As Integer

     Private Sub MenuExitProgram_Click( _
           ByVal sender As System.Object, _
           ByVal e As System.EventArgs) _
           Handles MenuExitProgram.Click
        ' ----- Exit the program.
        Me.Close()
     End Sub

     Private Sub Form1_Load(ByVal sender As Object, _
           ByVal e As System.EventArgs) Handles Me.Load
        ' ----- Scan through the user's "Favorites" and
        '       add them as menu items.
        Dim favoritesPath As String

        ' ----- Determine the location of the "Favorites"
        '       folder.
        favoritesPath = Environment.GetFolderPath( _ 
        Environment.SpecialFolder.Favorites)
        If (favoritesPath = "") Then Return
        If (My.Computer.FileSystem.DirectoryExists( _
           favoritesPath) = False) Then Return

        ' ----- Call the recursive routine that builds the menu.
        BuildFavorites(MenuFavorites, favoritesPath)

        ' ----- If favorites were added, hide the
        '       "no favorites" item.
        If (MenuFavorites.DropDownItems.Count > 1) Then _ 
         MenuNoFavorites.Visible = False  
     End Sub

     Private Sub BuildFavorites(ByVal whichMenu As _
           ToolStripMenuItem, ByVal fromPath As String)
        ' ----- Given a starting directory, add all files
        '       and directories in it to the specified menu.
        '       Recurse for suborindate directories.
        Dim oneEntry As String
        Dim menuEntry As ToolStripMenuItem
        Dim linkPath As String
        Dim displayName As String

        ' ----- Start with any directories.
        For Each oneEntry In My.Computer.FileSystem. _
              GetDirectories(fromPath)
           ' ----- Create the parent menu, but don't
           '       attach it yet.
           menuEntry = New ToolStripMenuItem( _ 
         My.Computer.FileSystem.GetName(oneEntry))

           ' ----- Recurse to build the sub-directory branch.
           BuildFavorites(menuEntry, oneEntry) 

           ' ----- If that folder contained items,
           '       then attach it.
          If (menuEntry.DropDownItems.Count > 0) Then _
           whichMenu.DropDownItems.Add(menuEntry) 
       Next oneEntry 

       ' ---- Next, build the actual file links. Only
       '      look at ".url" files.
       For Each oneEntry In My.Computer.FileSystem. _
             GetFiles(fromPath, FileIO.SearchOption. _
             SearchTopLevelOnly, "*.url")
          ' ----- Build a link based on this file. These
          '       files are old-style INI files.
          linkPath = GetINIEntry("InternetShortcut", _
             "URL", oneEntry)
          If (linkPath <> "") Then
             ' ----- Found the link. Add it to the menu.
             displayName = My.Computer.FileSystem. _
                GetName(oneEntry)
             displayName = MVB.Left(displayName, _
                displayName.Length - 4)
           menuEntry = New ToolStripMenuItem(displayName)
            menuEntry.Tag = linkPath
            whichMenu.DropDownItems.Add(menuEntry)

            ' ----- Connect this entry to the event handler.
            AddHandler menuEntry.Click, _
               AddressOf RunFavoritesLink
         End If
      Next oneEntry
   End Sub

   Private Sub RunFavoritesLink( _
         ByVal sender As System.Object, _
         ByVal e As System.EventArgs)
      ' ----- Run the link.
      Dim whichMenu As ToolStripMenuItem

      whichMenu = CType(sender, ToolStripMenuItem)
      Process.Start(whichMenu.Tag)
   End Sub

   Private Function GetINIEntry(ByVal sectionName As String, _
         ByVal keyName As String, _
         ByVal whichFile As String) As String
      ' ----- Extract a value from an INI-style file.
      Dim resultLength As Integer
      Dim targetBuffer As New System.Text.StringBuilder(500)

      resultLength = GetPrivateProfileString(sectionName, _
         keyName, "", targetBuffer, targetBuffer.Capacity, _

         whichFile)
      Return targetBuffer.ToString()
    End Function
  End Class

Run the program, and access its Favorites menu to browse and open the current user’s Internet Explorer favorites.

Discussion

The bulk of this recipe’s code deals with scanning through a directory structure and examining each file and subdirectory. Most of the files in the “Favorites” folder have a .url extension and contain data in an “INI file” format.

Here’s a sample link to a popular search engine:

  [DEFAULT]
  BASEURL=http://www.google.com/
  [InternetShortcut]
  URL=http://www.google.com/

The last “URL=” line provides the link we need to enable favorites support in our program.

The important part of the program is the building of the menu structure. Each menu item attached to the form’s main menuMenuStrip control is a relatedToolStripMenuItemclass instance. These can be attached to the menu at any time through itsDropDownItemscollection. Each menu item in turn has its ownDropDownItemscollection that manages subordinate menu items.

To make each new menu item do something, as you add them, connect them to the previously writtenRunFavoritesLinkmethod:

  AddHandler menuEntry.Click, AddressOf RunFavoritesLink

Next: 4.19 Creating Shortcut Menus >>
 

More Visual Basic.NET Articles
More By O'Reilly Media

Comments On: Focusing on Forms and Menus in Visual Basic

· This article is an excerpt from the book "Visual Basic 2005 Cookbook," published by...   >>> Post your comment now!

Buy this book...

This article is excerpted from chapter four of the Visual Basic 2005 Cookbook, written by Tim Patrick and John Clark Craig (O'Reilly; ISBN: 0596101775). Check it out today at your favorite bookstore. Buy this book now.