Passing Data

Last Updated: 9/19/2008

Sections above here:
Home » Development » Form Management

Sections below here:

Topics in this section:
Form Management
User Controls
IntraWeb Frame
Managing Forms
Form List
Showing Forms
Hiding Forms
Destroying Forms
Passing Data

Data can be passed between form just like in any normal application. Since forms are persistent information can be stored in member variables of form classes.

For demonstration purposes we will build a simple demo with two forms. The main form will contain a button and an edit box. The other form contains a memo field and a label. When the user presses the button on the main form the text from the edit box will be added to the memo on the second form and the form will be displayed. The second form will also display how many times it has been displayed and allow the user to return to the main form.

Complete Demo

To see the project in action, please see the FormData.dpr project in the Demos directory of IntraWeb for Delphi, or the FormData.sln in the Demos directory of IntraWeb for Visual Studio .NET. For the Visual Studio .NET version, the demo is available in both C# and VB.NET languages.

Delphi example

This is how the main form looks like at design time:

Main Form – Source Code:

unit Main;
{PUBDIST}

interface

uses
  IWAppForm, IWApplication, IWTypes, IWCompButton, IWCompEdit, Classes,
  Controls, IWControl, IWCompLabel, Dialog, IWHTMLControls;

type
  TformMain = class(TIWAppForm)
    IWLabel1: TIWLabel;
    editText: TIWEdit;
    butnOk: TIWButton;
    IWLink1: TIWLink;
    procedure butnOkClick(Sender: TObject);
    procedure IWAppFormCreate(Sender: TObject);
    procedure IWLink1Click(Sender: TObject);
  public
    FDialogForm: TformDialog;
  end;

implementation
{$R *.dfm}

uses
  SysUtils;

procedure TformMain.butnOkClick(Sender: TObject);
var
  s: string;
begin
  s := Trim(editText.Text);
  editText.Text := '';
  if s = '' then begin
    WebApplication.ShowMessage('Please enter some text.');
  end else begin
    with FDialogForm do begin
      IWMemo1.Lines.Add(s);
      Inc(FCount);
      Show;
    end;
  end;
end;

procedure TformMain.IWAppFormCreate(Sender: TObject);
begin
  FDialogForm := TformDialog.Create(WebApplication);
end;

procedure TformMain.IWLink1Click(Sender: TObject);
begin
  WebApplication.Terminate('Good bye!');
end;

end.

IWLink1 OnClick

This event is hooked to the link with the caption "Quit" and simply terminates the session when the user clicks the link.

OnCreate

The OnCreate event is called when the form is created. In this event another form is created and the reference to it is stored as a member variable of this form so it can be accessed again later.

butnOk.OnClick

If the user did enter data, using FDialogForm (which was created in this form's OnCreate) is used. Data is added to the memo, and a member variable of TFormDialog is updated. It is then displayed using the .Show method. As you can see, data is very easy to pass between forms and is the same as in a normal Delphi application.

Visual Studio .NET example

The forms are called: FormMain and FormDialog

FormMain - Design time

FormMain - C# source code:

using System; 
using System.Collections; 
using System.ComponentModel; 
using System.Drawing; 
using System.Windows.Forms; 
using System.Data; 
using Atozed.IntraWeb.NETMain; 
using Atozed.IntraWeb.AppFormUnit; 

namespace FormData 
{ 

   public class FormMain : AppForm 
   { 
      private Atozed.IntraWeb.CompLabel.TextLabel tiwLabel1; 
      private Atozed.IntraWeb.CompEdit.Edit editText; 
      private Atozed.IntraWeb.CompButton.Button btnOk; 
      private Atozed.IntraWeb.HTMLControls.Link lnkQuit; 
      private System.ComponentModel.Container components = null; 
      private FormDialog formDialog = new FormDialog();  

      public FormMain() 
      { 
         // This call is required by the Windows Form Designer. 
         InitializeComponent(); 

         // TODO: Add any initialization after the InitializeComponent call 
      } 

      /// 
  
    /// Clean up any resources being used. /// 
  

  protected override void Dispose(bool disposing) { if (disposing) { if (components != null) { components.Dispose();
  } } base.Dispose(disposing); } #region Designer generated code /// 
  
    /// Required method for Designer support - do not modify /// the contents of this method with the code
    editor. /// 
  

  private void InitializeComponent() { } #endregion #region Application entry point /// 
  
    /// The main entry point for the application. /// 
  

  [STAThread] static void Main() { IWServerController.SetServerControllerClass(typeof(IWServerController));
  new IWLicenseKey(); FormMain.SetAsMainForm(typeof(FormMain)); Application.Run(new Main()); } #endregion
  private void btnOk_OnClick(object sender, System.EventArgs e) { string s = ""; if (editText.Text != null)
  { s = editText.Text.Trim(); } if ("" == s) { WebApplication.ShowMessage("Please enter some text."); }
  else { formDialog.GetMemoControl().Lines.Add(s); formDialog.Count += 1; formDialog.Show(); } } private
  void lnkQuit_OnClick(object sender, System.EventArgs e) { WebApplication.Terminate("Good bye!"); } } }

FormMain - VB.NET source code

Imports System 
Imports System.Collections 
Imports System.ComponentModel 
Imports System.Drawing 
Imports System.Windows.Forms 
Imports System.Data 
Imports Atozed.IntraWeb.NETMain 
Imports Atozed.IntraWeb.AppFormUnit 

Public Class FormMain 
   Inherits AppForm 
   Private WithEvents TiwLabel1 As Atozed.IntraWeb.CompLabel.TextLabel 
   Private WithEvents editText As Atozed.IntraWeb.CompEdit.Edit 
   Private components As System.ComponentModel.Container = Nothing 
   Private frmDialog As FormDialog = New FormDialog 

   Public Sub New() 
      ' This call is required by the Windows Form Designer. 
      InitializeComponent() 

      ' TODO: Add any initialization after the InitializeComponent call 
   End Sub 

   '  
   ' Clean up any resources being used. 
   ' 
 
   Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean) 
      If disposing Then 
         If Not components Is Nothing Then 
            components.Dispose() 
         End If 
      End If 
      MyBase.Dispose(disposing) 
   End Sub 

   #Region "Designer generated code" 
   '  
   ' Required method for Designer support - do not modify 
   ' the contents of this method with the code editor. 
   ' 
 
   Private WithEvents btnOk As Atozed.IntraWeb.CompButton.Button 
   Private WithEvents lnkQuit As Atozed.IntraWeb.HTMLControls.Link 
   Private Sub InitializeComponent() 

   End Sub 
   #End Region 
   
   #Region "Application entry point" 
   '///  
   '/// The main entry point for the application. 
   '/// 
 
    _ 
   Shared Sub Main()  
      Dim LLicense As IWLicenseKey = new IWLicenseKey() 
      IWServerController.SetServerControllerClass(System.Type.GetType("FormData.IWServerController")) 
      FormMain.SetAsMainForm(System.Type.GetType("FormData.FormMain")) 
      Application.Run(new Main()) 
   End Sub 
   #End Region        

   Private Sub lnkQuit_OnClick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles lnkQuit.OnClick 
      WebApplication.Terminate("Good bye!") 
   End Sub 

   Private Sub btnOk_OnClick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnOk.OnClick 
      Dim s As String = "" 
      If (editText.Text <> Nothing) Then 
         s = editText.Text.Trim() 
      End If 
      If ("" = s) Then 
         WebApplication.ShowMessage("Please enter some text.") 
      Else 
         frmDialog.GetMemoControl().Lines.Add(s) 
         frmDialog.Count = frmDialog.Count + 1 
         frmDialog.Show() 
      End If 
   End Sub 
End Class

Form this example the code generated by the form designer in the InitializeComponent method was removed.

btnOk_OnClick

In the OnClick event the edit box is checked for data. If no data exists WebApplication.ShowMessage is called to display a message to the user. After the message is dismissed the main form is shown again. If the user did enter data, using FDialogForm (which was created in this form's OnCreate) is used. Data is added to the memo, and a member variable of TFormDialog is updated. It is then displayed using the .Show method. As you can see, data is very easy to pass between forms and is the same as in a normal Delphi application.

lnkQuit_OnClick

This event terminates the session.

Note for C++ Builder users

Due to the way forms work in C++ Builder, the best place to initialize all automatic class instances is inside the form constructor rather than within the OnCreate event handler.

This will avoid the problem of instances being created twice, problem that arises because of the creation order of the form elements in C++ Builder. In C++ Builder the OnCreate event handler is called before the form constructor, and the OnDestroy event handler is called after the form destructor.

To avoid such problems, please move all the automatic class instances initialization in the form constructor, and keep in the OnCreate event handler only the dynamically allocated instances.