All set. Back to the project
Now, add a ListBox and two Button components from the "Web Controls" group on the "Tool Palette" window. Name the two buttons "AddItemButton" and "RemoveItemButton" (read this as "change the ID property in the Misc group to..."). The ListBox could carry the default ListBox1 name.

The idea is to let the user enter new items in the ListBox, remove the selected item or delete all the items from the ListBox. We'll use the InputBox function from the Mono Dialogs package which displays a web based input dialog box that lets the user enter a string - in our case the item text. To enable item deletion from the list, we'll put MessageDlg in action. The MessageDlg function creates, displays, and operates a web based message box - the same way as you are used to in classic desktop applications.

First, make sure you add "MonoSoftware.Web.Dialogs" to the uses list in the interface part of the web form page-behind class.

Note: it would be wise to open the Documentation that comes with the MonoSoftware.Web.Dialogs component to get familiar with the dialogs and the call parameters.

Next, add the following code to the Page_Load procedure:

procedure TMonoDialogs.Page_Load
  (sender: System.Object; e: System.EventArgs);
begin
  if not Page.IsPostBack then
  // only first time
  begin
    ListBox1.Items.Add('http://delphi.about.com');
    ListBox1.Items.Add('http://aspxDelphi.net');
    ListBox1.Items.Add('http://www.mono-software.com');
  end;

  NewItem := Dialogs.InputBox(AddItemButton,
                              'Add an item to ListBox',
                              'New item name',
                              'A new item');

  DoRemoveItem := Dialogs.MessageDlg(RemoveItemButton,
      'Are you sure you want to remove the 
       selected item from the list?' + #13#10 +
      'Select [All] to remove all Items!',
      'Removing an item',
      TDlgType.mtConfirmation,
      TMsgDlgBtn.mbAll or 
      TMsgDlgBtn.mbYes or 
      TMsgDlgBtn.mbCancel,
      False);
end;

Let's see what's happening in the Page_Load event handler:
First, we fill in some initial items in the List Box making sure that the code executes only *once* - or better to say only the first time we access the page. On every postback this code (the "if Not Page.IsPostback..." block) will not execute.

Note: you need to add two unit level variables that hold the resulting values from the call to the InputBox and MessageDlg.

...
implementation

var
  NewItem: string;
  DoRemoveItem : TMsgDlgResult;
  
...

Next, we attach an InputBox to a call to the AddItemButton. Every time a user presses a button - an InputBox will popup asking for a new item entry. If the user presses "Cancel" nothing will happen (postback "canceled"). However, if the "Ok" button is picked a postback will occur and the code in the AddItemButton's Click event handler will execute. The NewItem string variable holds the string value the user typed into the InputBox.

procedure TMonoDialogs.AddItemButton_Click
  (sender: System.Object; e: System.EventArgs);
begin
  ListBox1.Items.Add(NewItem);
end;

To enable a user to remove the selected item from the ListBox we'll use the MessageDlg function. Again, the DoRemoveItem variable (of the Dialogs.TMsgDlgResult type) is used to hold the return value from a call to the MessageDlg function. Note that we indicated that three buttons should appear on the dialog. The Cancel button (by default) cancels the postback; the Yes button tells us that the user whishes to delete only the selected item; and the All button provides a user with an option to clear the list box.

If any of the All or Yes buttons we selected the code inside the RemoveItemButton's Click event handler will execute. This is what will happen ...

procedure TMonoDialogs.RemoveItemButton_Click
  (sender: System.Object; e: System.EventArgs);
begin
  if DoRemoveItem = TmsgDlgResult.mrAll then
  begin
    ListBox1.Items.Clear;
  end
  else
  begin
    if ListBox1.SelectedIndex > 0 then
      ListBox1.Items.RemoveAt(ListBox1.SelectedIndex)
    else
      Dialogs.ShowMessage(Page,
                          'Nothing was selected',
                          'Operation failed',
                          TDlgType.mtWarning);
  end
end;

The code above uses the third dialog function from the Mono.Web.Dialogs assembly. The ShowMessage simply displays a warning to the user that nothing was selected.

And that does it! As simple as in any desktop application. Well, more or less... there are some rules you have to follow when building web applications. For example, you CANNOT attach an InputBox to a button in a Button Click handling procedure - simply because the dialog must be attached to the Button in an earlier event - like Page_Init or Page_Load. If you try to attach an InputBox to a Button inside its own Click handling procedure ... the InputBox will appear one postback too late.
Hm, this sounds to much complicated for this chapter .. we'll deal with page processing and postback some other time.

Hey, this is the .Net world!
Final note: have I mentioned the language the Mono Dialogs are built with? I haven't! Why? It's simple: this is .Net - who cares abut the actual language (even though you have to admit that "TDlgType.mtWarning" looks quite familiar)!

To the next chapter: A Beginner's Guide to Asp.Net Programming for Delphi developers

If you need any kind of help at this point, please post to the Delphi Programming Forum where all the questions are answered and beginners are treated as experts.