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Form in DLL: what changed

Revision 0 to 1. Removed lines have a minus sign; added lines have a plus sign.

Title: Form in DLL

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1+The following application and library demonstrate you how to show a modal and a non-modal form and create a custom component on application form from a DLL library. Tested on win32 and Linux/Gtk2 with Lazarus 1.7 trunk.
2+
3+Main application:
4+
5+``` Pascal
6+program MainApp;
7+
8+uses
9+ Interfaces, Classes, LCLType, Controls, StdCtrls, Forms, ExtCtrls;
10+
11+type
12+ TEnableDisableFormsCallBack = procedure(var FormList: Pointer);
13+ TCreateButtonCallBack = procedure(Caption: PChar; OnClick: TProcedure);
14+
15+const
16+{$IFDEF WINDOWS}
17+ DLLDialogLib = 'DLLDialog.dll';
18+{$ELSE}
19+ DLLDialogLib = 'DLLDialog.so';
20+{$ENDIF}
21+
22+procedure DLLDialog_Init(DisableFormsCallBack, EnableFormsCallback: TEnableDisableFormsCallBack); external DLLDialogLib;
23+procedure DLLDialog_Final; external DLLDialogLib;
24+procedure DLLDialog_ShowModal(ParentWindow: HWND); external DLLDialogLib;
25+procedure DLLDialog_Show(ParentWindow: HWND); external DLLDialogLib;
26+procedure DLLDialog_CreateDLLButton(ParentWindow: HWND); external DLLDialogLib;
27+procedure DLLDialog_CreateButton(CreateButtonCallBack: TCreateButtonCallBack); external DLLDialogLib;
28+
29+type
30+ TMainForm = class(TForm)
31+ private
32+ PnlParent: TPanel;
33+
34+ procedure BtnAddDLLButtonClick(Sender: TObject);
35+ procedure BtnAddButtonClick(Sender: TObject);
36+ procedure ShowModalDLLDialog(Sender: TObject);
37+ procedure ShowDLLDialog(Sender: TObject);
38+ public
39+ constructor Create(aOwner: TComponent); override;
40+ end;
41+
42+var
43+ MainForm: TMainForm;
44+
45+{ TMainForm }
46+
47+procedure DisableFormsCallBack(var FormList: Pointer);
48+begin
49+ FormList := Screen.DisableForms(nil, TList(FormList));
50+end;
51+
52+procedure EnableFormsCallback(var FormList: Pointer);
53+begin
54+ Screen.EnableForms(TList(FormList));
55+end;
56+
57+constructor TMainForm.Create(aOwner: TComponent);
58+var
59+ BtnShow, BtnShowModal, BtnAddDLLButton, BtnAddButton: TButton;
60+begin
61+ inherited CreateNew(aOwner);
62+
63+ Position := poWorkAreaCenter;
64+ Width := 600;
65+ Height := 200;
66+
67+ BtnShow := TButton.Create(Self);
68+ BtnShow.Parent := Self;
69+ BtnShow.Caption := 'Show form';
70+ BtnShow.AutoSize := True;
71+ BtnShow.OnClick := @ShowDLLDialog;
72+
73+ BtnShowModal := TButton.Create(Self);
74+ BtnShowModal.Parent := Self;
75+ BtnShowModal.Caption := 'Show modal form';
76+ BtnShowModal.AutoSize := True;
77+ BtnShowModal.OnClick := @ShowModalDLLDialog;
78+ BtnShowModal.AnchorSide[akLeft].Control := BtnShow;
79+ BtnShowModal.AnchorSide[akLeft].Side := asrRight;
80+ BtnShowModal.BorderSpacing.Left := 10;
81+
82+ BtnAddDLLButton := TButton.Create(Self);
83+ BtnAddDLLButton.Parent := Self;
84+ BtnAddDLLButton.Caption := 'Create real DLL button';
85+ BtnAddDLLButton.AutoSize := True;
86+ BtnAddDLLButton.OnClick := @BtnAddDLLButtonClick;
87+ BtnAddDLLButton.AnchorSide[akLeft].Control := BtnShowModal;
88+ BtnAddDLLButton.AnchorSide[akLeft].Side := asrRight;
89+ BtnAddDLLButton.BorderSpacing.Left := 10;
90+
91+ BtnAddButton := TButton.Create(Self);
92+ BtnAddButton.Parent := Self;
93+ BtnAddButton.Caption := 'Create fake DLL button';
94+ BtnAddButton.AutoSize := True;
95+ BtnAddButton.OnClick := @BtnAddButtonClick;
96+ BtnAddButton.AnchorSide[akLeft].Control := BtnAddDLLButton;
97+ BtnAddButton.AnchorSide[akLeft].Side := asrRight;
98+ BtnAddButton.BorderSpacing.Left := 10;
99+
100+ PnlParent := TPanel.Create(Self);
101+ PnlParent.Parent := Self;
102+ PnlParent.AnchorSide[akTop].Control := BtnShow;
103+ PnlParent.AnchorSide[akTop].Side := asrBottom;
104+ PnlParent.BorderSpacing.Top := 10;
105+ PnlParent.Width := 220;
106+end;
107+
108+procedure CreateButtonCallBack(ACaption: PChar; AOnClick: TProcedure);
109+var
110+ Btn: TButton;
111+ MyMethod: TMethod;
112+begin
113+ Btn := TButton.Create(MainForm);
114+ Btn.Caption := ACaption;
115+ Btn.Left := 100;
116+ Btn.Width := 100;
117+ Btn.Height := 20;
118+ MyMethod.Code := AOnClick;
119+ MyMethod.Data := nil;
120+ Btn.OnClick := TNotifyEvent(MyMethod);
121+ Btn.Parent := MainForm.PnlParent;
122+end;
123+
124+procedure TMainForm.BtnAddButtonClick(Sender: TObject);
125+begin
126+ DLLDialog_CreateButton(@CreateButtonCallBack);
127+end;
128+
129+procedure TMainForm.BtnAddDLLButtonClick(Sender: TObject);
130+begin
131+ DLLDialog_CreateDLLButton(PnlParent.Handle);
132+end;
133+
134+procedure TMainForm.ShowDLLDialog(Sender: TObject);
135+begin
136+ DLLDialog_Show(0);
137+end;
138+
139+procedure TMainForm.ShowModalDLLDialog(Sender: TObject);
140+begin
141+ DLLDialog_ShowModal(Self.Handle);
142+end;
143+
144+{$R *.res}
145+
146+begin
147+ Application.Initialize;
148+ Application.CreateForm(TMainForm, MainForm);
149+ DLLDialog_Init(@DisableFormsCallBack, @EnableFormsCallback);
150+ try
151+ Application.Run;
152+ finally
153+ DLLDialog_Final;
154+ end;
155+end.
156+```
157+
158+DLL with a form:
159+
160+``` Pascal
161+library DllDialog;
162+
163+{$mode objfpc}{$H+}
164+
165+uses
166+ Interfaces, Classes, LCLType, StdCtrls, Controls, Forms, Dialogs;
167+
168+type
169+ TDLLDialog = class(TForm)
170+ protected
171+ procedure CreateParams(var Params: TCreateParams); override;
172+ public
173+ procedure BtnShowMessageClick(Sender: TObject);
174+ constructor Create(aOwner: TComponent); override;
175+ public
176+ ParentFormHandle: HWND;
177+ end;
178+
179+ TEnableDisableFormsCallBack = procedure(var FormList: Pointer);
180+ TCreateButtonCallBack = procedure(Caption: PChar; OnClick: TProcedure);
181+
182+ TApplicationCallback = class(TComponent)
183+ private
184+ DisableFormsCallBack: TEnableDisableFormsCallBack;
185+ EnableFormsCallback: TEnableDisableFormsCallBack;
186+ FormList: Pointer;
187+ public
188+ procedure DisableForms(Sender: TObject);
189+ procedure EnableForms(Sender: TObject);
190+ procedure BtnClick(Sender: TObject);
191+
192+ constructor Create(aOwner: TComponent); override;
193+ destructor Destroy; override;
194+ end;
195+
196+var
197+ ApplicationCallback: TApplicationCallback;
198+
199+procedure DLLDialog_Init(DisableFormsCallBack, EnableFormsCallback: TEnableDisableFormsCallBack);
200+begin
201+ ApplicationCallback := TApplicationCallback.Create(nil);
202+ ApplicationCallback.DisableFormsCallBack := DisableFormsCallBack;
203+ ApplicationCallback.EnableFormsCallback := EnableFormsCallback;
204+end;
205+
206+procedure DLLDialog_Final;
207+begin
208+ ApplicationCallback.Free;
209+end;
210+
211+procedure DLLDialog_ShowModal(ParentWindow: HWND);
212+var
213+ DLLDialog: TDLLDialog;
214+begin
215+ DLLDialog := TDLLDialog.Create(ApplicationCallback);
216+ try
217+ DLLDialog.ParentFormHandle := ParentWindow;
218+ DLLDialog.ShowModal;
219+ finally
220+ DLLDialog.Free;
221+ end;
222+end;
223+
224+procedure DLLDialog_Show(ParentWindow: HWND);
225+var
226+ DLLDialog: TDLLDialog;
227+begin
228+ DLLDialog := TDLLDialog.Create(ApplicationCallback);
229+ DLLDialog.ParentFormHandle := ParentWindow;
230+ DLLDialog.Show;
231+end;
232+
233+procedure DLLDialog_CreateDLLButton(ParentWindow: HWND);
234+var
235+ Btn: TButton;
236+ BtnParentForm: TForm;
237+begin
238+ BtnParentForm := TForm.CreateNew(ApplicationCallback);
239+ BtnParentForm.ParentWindow := ParentWindow;
240+ BtnParentForm.Width := 100;
241+ BtnParentForm.Height := 20;
242+ BtnParentForm.BorderStyle := bsNone;
243+ BtnParentForm.Visible := True;
244+
245+ Btn := TButton.Create(ApplicationCallback);
246+ Btn.Caption := 'Real DLL Button';
247+ Btn.Width := BtnParentForm.Width;
248+ Btn.Height := BtnParentForm.Height;
249+ Btn.OnClick := @ApplicationCallback.BtnClick;
250+ Btn.Parent := BtnParentForm;
251+end;
252+
253+procedure FakeBtnClick;
254+begin
255+ ShowMessage('You clicked a fake button from a DLL!');
256+end;
257+
258+procedure DLLDialog_CreateButton(CreateButtonCallBack: TCreateButtonCallBack);
259+begin
260+ CreateButtonCallBack('Fake DLL Button', @FakeBtnClick);
261+end;
262+
263+exports
264+ DLLDialog_Init, DLLDialog_Final, DLLDialog_ShowModal, DLLDialog_Show,
265+ DLLDialog_CreateButton, DLLDialog_CreateDLLButton;
266+
267+{ TApplicationCallback }
268+
269+constructor TApplicationCallback.Create(aOwner: TComponent);
270+begin
271+ inherited Create(aOwner);
272+
273+ Application.AddOnModalBeginHandler(@DisableForms);
274+ Application.AddOnModalEndHandler(@EnableForms);
275+end;
276+
277+procedure TApplicationCallback.BtnClick(Sender: TObject);
278+begin
279+ ShowMessage('You clicked a real button from a DLL!');
280+end;
281+
282+destructor TApplicationCallback.Destroy;
283+begin
284+ Application.RemoveOnModalBeginHandler(@DisableForms);
285+ Application.RemoveOnModalEndHandler(@EnableForms);
286+
287+ inherited Destroy;
288+end;
289+
290+procedure TApplicationCallback.DisableForms(Sender: TObject);
291+begin
292+ DisableFormsCallBack(FormList);
293+end;
294+
295+procedure TApplicationCallback.EnableForms(Sender: TObject);
296+begin
297+ EnableFormsCallback(FormList);
298+end;
299+
300+{ TDLLDialog }
301+
302+constructor TDLLDialog.Create(aOwner: TComponent);
303+var
304+ BtnShowMessage: TButton;
305+begin
306+ inherited CreateNew(aOwner);
307+
308+ Caption := 'This form is in a DLL !!!';
309+ Position := poWorkAreaCenter;
310+ Width := 200;
311+ Height := 100;
312+
313+ BtnShowMessage := TButton.Create(Self);
314+ BtnShowMessage.Parent := Self;
315+ BtnShowMessage.Caption := 'Show message';
316+ BtnShowMessage.AutoSize := True;
317+ BtnShowMessage.OnClick := @BtnShowMessageClick;
318+end;
319+
320+procedure TDLLDialog.BtnShowMessageClick(Sender: TObject);
321+begin
322+ ShowMessage('Hello from DLL!');
323+end;
324+
325+procedure TDLLDialog.CreateParams(var Params: TCreateParams);
326+begin
327+ inherited CreateParams(Params);
328+
329+ {$IFDEF LCLWin32}
330+ Params.WndParent := ParentFormHandle;
331+ {$ENDIF}
332+end;
333+
334+begin
335+ Application.Initialize;
336+end.
337+```
338+
339+---
340+*From the Free Pascal wiki, page "Form in DLL", as it stood on 2020-02-15 after a change by Trev, out of the wiki's dump of 2024-05-26. Copyright stays with the author who wrote it, according to the old wiki's [[Licensing]] page. If you have concerns about this material, [message the admin](/wiki-contact).*

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