Question

It appears that VB in VS8 doesn’t support/convert lambda expressions with a statement body. I’m using them in my C# application, but now must convert it to VB.

I’m creating a whole bunch of controls dynamically, and I want to be able to give them event handlers on the fly. This is so I can build a dynamic user interface from a database. In the following code I’ll create a form and a checkbox, make the checkbox control the form’s visibility, add a few method handlers to the form, and then add the newly created checkbox to a pre-existing form/panel/etc. Handlers for the form, for instance, affect the checkbox:

  // Inside some loop creating a lot of these forms and matching checkboxes
      Form frmTemp = frmTestPanels[i];  // New form in array
      CheckBox chkSelectPanel;          // New checkbox that selects this panel
      chkSelectPanel = new CheckBox();
      chkSelectPanel.Text = SomeName;   // Give checkbox a label
      chkSelectPanel.Click += (ss, ee) =>  // When clicked
      {
          label1.Text = SomeName;       // Update a label
          if (chkSelectPanel.Checked)   // Show or hide the form
          {
              frmTemp.Show();
          }
          else
          {
              frmTemp.Hide();
          }
      };

      frmTemp.VisibleChanged += (ss, ee) =>  // When form visibility changes
      {
          chkSelectPanel.Checked = frmTemp.Visible;  // Reflect change to checkbox
          ConfigurationFileChanged = true;   // Update config file later
      };

      frmTemp.FormClosing += (ss, ee) =>     // When the form closes
      {   // We're only pretending to close the form - it'll sit around until needed
          chkSelectPanel.Checked = false;    // Update the checkbox
          frmTemp.Hide();                    // Hide the form
          ee.Cancel = true;                  // Cancel the close
      };

      flpSelectGroup.Controls.Add(chkSelectPanel); // Add checkbox to flow layout panel
  // End of loop creating a bunch of these matching forms/checkboxes

Of course, I’m getting the conversion error:

VB does not support anonymous methods/lambda expressions with a statement body

I really liked the ability to create everything on the fly, and then let the objects handle themselves – I don’t need to add any special functions that figure out which form is giving the close event so it can search for the right checkbox and update the checkbox – It Just Works (TM).

Unfortunately it needs to be converted to VB.

What is the best way to convert lambda/anonymous statement bodies into something that will work in VB, especially when one needs to create many of them?

Answer 1

Wait for the nearest release of .NET 4, it will support things like this in VB. Don’t see other alternative.

Ugly alternatives are:

1. This work, but you can use a single statement in a function.

   AddHandler Me.Click, Function(o, e) MessageBox.Show("text")
   

2. Create some regular Sub Foo

   Public Sub Foo(ByVal o As Object, ByVal e As EventArgs)
        MessageBox.Show("text")
   End Sub
   

   and use AddHandler to bind it to an event

   AddHandler Me.Click, AddressOf Foo