Create MDI Windows

unit CreateMDIWindowU;

interface

uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls, Menus;

type
  TForm1 = class(TForm)
    MainMenu1: TMainMenu;
    CreateChild1: TMenuItem;
    procedure CreateChild1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.DFM}

{ Register the MDI Child Window Class }
function RegisterClass: Boolean;
var
  WindowClass: TWndClass;
begin
  {setup our new window class}
  WindowClass.Style := CS_HREDRAW or CS_VREDRAW;           {set the class styles}
  WindowClass.lpfnWndProc := @DefMDIChildProc;             {point to the default MDI child window procedure}
  WindowClass.cbClsExtra := 0;                             {no extra class memory}
  WindowClass.cbWndExtra := 0;                             {no extra window memory}
  WindowClass.hInstance := hInstance;                      {the application instance}
  WindowClass.hIcon := LoadIcon(0, IDI_WINLOGO);           {load a predefined logo}
  WindowClass.hCursor := LoadCursor(0, IDC_APPSTARTING);   {load a predefined cursor}
  WindowClass.hbrBackground := COLOR_WINDOW;               {use a predefined color}
  WindowClass.lpszMenuName := nil;                         {no menu}
  WindowClass.lpszClassName := 'TestClass';                {the registered class name}

  {now that we have our class set up, register it with the system}
  Result := Windows.RegisterClass(WindowClass) <> 0;
end;

procedure TForm1.CreateChild1Click(Sender: TObject);
var
  hWindow: HWND;
begin
  {register our new class first}
  if not RegisterClass then
  begin
    ShowMessage('RegisterClass failed');
    Exit;
  end;

  {now, create a window based on our new class}
  hWindow := CreateMDIWindow('TestClass',           {the registered class name}
                             'API Window',          {the title bar text}
                             WS_VISIBLE OR          {the MDI child window is visible,}
                             WS_CAPTION OR          {has a caption bar,}
                             WS_SYSMENU OR          {a system menu,}
                             WS_MINIMIZEBOX OR      {and minimize and}
                             WS_MAXIMIZEBOX,        {maximize boxes}
                             CW_USEDEFAULT,         {default horizontal position}
                             CW_USEDEFAULT,         {default vertical position}
                             CW_USEDEFAULT,         {default width}
                             CW_USEDEFAULT,         {default height}
                             Form1.ClientHandle,    {handle of the MDI client window}
                             hInstance,             {the application instance}
                             0                      {no additional information}
                             );

  {if our window was created successfully, show it}
  if hWindow <> 0 then
  begin
    ShowWindow(hWindow, SW_SHOWNORMAL);
    UpdateWindow(hWindow);
  end
  else
  begin
    ShowMessage('CreateWindow failed');
    Exit;
  end;

end;
end.