Creating replacement TApplication for experimentation? - delphi

Question

I got the crazy idea one day to make a completely new replacement of TApplication for experimentation. I got everything to compile and run, and it does show the main form properly, everything responds good, but upon closing the form, the application does not halt. I'm sure I copied all the necessary stuff from the original Forms.pas TApplication (registering close event) but I don't see it working. I have to terminate the debug session the nasty way.
My goal in this little experiment is to build a lightweight application for very simple things instead of all the possible things a TApplication can handle, and also mostly so I have some good experience in such a field.
Here's the unit as I have it now, and below is the implementation of it.
unit JDForms;
interface
uses
Forms, Classes, SysUtils, StrUtils, Windows, Win7, XPMan, Variants,
Messages, Dialogs;
type
TJDForm = class;
TJDApplication = class;
TJDApplicationThread = class;
TJDForm = class(TCustomForm)
private
public
published
end;
TJDApplication = class(TComponent)
private
fRunning: Bool;
fTerminated: Bool;
fThread: TJDApplicationThread;
fMainForm: TJDForm;
fOnMessage: TMessageEvent;
fShowMainForm: Bool;
fHandle: HWND;
procedure ThreadTerminated(Sender: TObject);
procedure HandleMessage;
procedure ProcessMessages;
function ProcessMessage(var Msg: TMsg): Boolean;
procedure ThreadSync(Sender: TObject);
public
constructor Create(AOwner: TComponent); override;
property Thread: TJDApplicationThread read fThread;
procedure Initialize;
procedure Run;
procedure CreateForm(InstanceClass: TComponentClass; var Reference);
procedure Terminate;
property Terminated: Bool read fTerminated;
procedure HandleException(Sender: TObject);
property Handle: HWND read fHandle;
published
property ShowMainForm: Bool read fShowMainForm write fShowMainForm;
property OnMessage: TMessageEvent read fOnMessage write fOnMessage;
end;
TJDApplicationThread = class(TThread)
private
fOwner: TJDApplication;
fStop: Bool;
fOnSync: TNotifyEvent;
procedure DoSync;
protected
procedure Execute; override;
public
constructor Create(AOwner: TJDApplication);
destructor Destroy; override;
procedure Start;
procedure Stop;
published
property OnSync: TNotifyEvent read fOnSync write fOnSync;
end;
var
JDApplication: TJDApplication;
implementation
procedure DoneApplication;
begin
with JDApplication do begin
if Handle <> 0 then ShowOwnedPopups(Handle, False);
//ShowHint := False;
Destroying;
DestroyComponents;
end;
end;
{ TJDApplication }
constructor TJDApplication.Create(AOwner: TComponent);
begin
fRunning:= False;
fTerminated:= False;
fMainForm:= nil;
fThread:= TJDApplicationThread.Create(Self);
fThread.FreeOnTerminate:= True;
fThread.OnTerminate:= ThreadTerminated;
fShowMainForm:= True;
end;
procedure TJDApplication.CreateForm(InstanceClass: TComponentClass; var Reference);
var
Instance: TComponent;
begin
Instance:= TComponent(InstanceClass.NewInstance);
TComponent(Reference) := Instance;
try
Instance.Create(Self);
except
TComponent(Reference):= nil;
raise;
end;
if (fMainForm = nil) and (Instance is TForm) then begin
TForm(Instance).HandleNeeded;
fMainForm:= TJDForm(Instance);
end;
end;
procedure TJDApplication.HandleException(Sender: TObject);
begin
{
if GetCapture <> 0 then SendMessage(GetCapture, WM_CANCELMODE, 0, 0);
if ExceptObject is Exception then
begin
if not (ExceptObject is EAbort) then
if Assigned(FOnException) then
FOnException(Sender, Exception(ExceptObject))
else
ShowException(Exception(ExceptObject));
end else
SysUtils.ShowException(ExceptObject, ExceptAddr);
}
end;
procedure TJDApplication.HandleMessage;
var
Msg: TMsg;
begin
if not ProcessMessage(Msg) then begin
//Idle(Msg);
end;
end;
function TJDApplication.ProcessMessage(var Msg: TMsg): Boolean;
var
Handled: Boolean;
begin
Result := False;
if PeekMessage(Msg, 0, 0, 0, PM_REMOVE) then
begin
Result := True;
if Msg.Message <> WM_QUIT then begin
Handled := False;
if Assigned(FOnMessage) then FOnMessage(Msg, Handled);
//if not IsHintMsg(Msg) and not Handled and not IsMDIMsg(Msg) and
//not IsKeyMsg(Msg) and not IsDlgMsg(Msg) then
begin
TranslateMessage(Msg);
DispatchMessage(Msg);
end;
end else begin
fTerminated:= True;
end;
end;
end;
procedure TJDApplication.ProcessMessages;
var
Msg: TMsg;
begin
while ProcessMessage(Msg) do {loop};
end;
procedure TJDApplication.Initialize;
begin
if InitProc <> nil then TProcedure(InitProc);
end;
procedure TJDApplication.Run;
begin {
fRunning := True;
try
AddExitProc(DoneApplication);
if FMainForm <> nil then
begin
case CmdShow of
SW_SHOWMINNOACTIVE: FMainForm.FWindowState := wsMinimized;
SW_SHOWMAXIMIZED: MainForm.WindowState := wsMaximized;
end;
if FShowMainForm then
if FMainForm.FWindowState = wsMinimized then
Minimize else
FMainForm.Visible := True;
repeat
try
HandleMessage;
except
HandleException(Self);
end;
until Terminated;
end;
finally
FRunning := False;
end;
}
fRunning:= True;
try
AddExitProc(DoneApplication);
if fMainForm <> nil then begin
fHandle:= fMainForm.Handle;
if fShowMainForm then begin
fMainForm.Show;
end;
fThread.Start;
repeat
try
HandleMessage;
//--- THREAD HANDLING MESSAGES ---
except
HandleException(Self);
end;
until fTerminated;
end else begin
//Main form is nil - can not run
end;
finally
fRunning:= False;
fTerminated:= True;
end;
end;
procedure TJDApplication.Terminate;
begin
fTerminated:= True;
try
fThread.Stop;
except
end;
if CallTerminateProcs then PostQuitMessage(0);
end;
procedure TJDApplication.ThreadTerminated(Sender: TObject);
begin
//Free objects
end;
procedure TJDApplication.ThreadSync(Sender: TObject);
var
Msg: TMsg;
begin
if not ProcessMessage(Msg) then begin
//Idle(Msg);
end;
end;
{ TJDApplicationThread }
constructor TJDApplicationThread.Create(AOwner: TJDApplication);
begin
inherited Create(True);
fOwner:= AOwner;
end;
destructor TJDApplicationThread.Destroy;
begin
inherited;
end;
procedure TJDApplicationThread.DoSync;
begin
Self.fOwner.ThreadSync(Self);
// if assigned(fOnSync) then fOnSync(Self);
end;
procedure TJDApplicationThread.Execute;
var
ST: Integer;
begin
ST:= 5;
fStop:= False;
while (not Terminated) and (not fStop) do begin
//----- BEGIN -----
Synchronize(DoSync);
//----- END -----
//Sleep(1000 * ST);
end;
end;
procedure TJDApplicationThread.Start;
begin
fStop:= False;
Resume;
end;
procedure TJDApplicationThread.Stop;
begin
fStop:= True;
Suspend;
end;
initialization
JDApplication:= TJDApplication.Create(nil);
finalization
if assigned(JDApplication) then begin
JDApplication.Free;
JDApplication:= nil;
end;
end.
And here's an application using this:
program Win7FormTestD7;
uses
Forms,
W7Form1 in 'W7Form1.pas' {Win7Form1},
JDForms in 'JDForms.pas';
begin
JDApplication.Initialize;
JDApplication.CreateForm(TWin7Form1, Win7Form1);
JDApplication.Run;
end.
The form 'W7Form1' is just a plain form with a couple random controls on it to test with.
Users here should not ask the question of why I want to do this, I have my reasons. I learn by doing, not by someone showing me or by reading some book or finding a bunch of code which I don't know how it works. This is a way for me to better learn the workings of applications and be able to expand my knowledge in the field to be able to build more complex applications in the future.

Answer 1

Keep in mind that TCustomForm has no concept of your TJDApplication class, it only works with the Forms.TApplication class instead. Make sure your TJDApplication.Run() method is exiting when the Forms.TApplication.Terminated property has been set to True.

Answer 2

If building lightweight application is your motto, I suggest you to play around with :
The KOL Library
The SDA Framework
VCL Light by Paul TOTH
LVCL based on VCL Light code by SO member Arnaud Bouchez.