This document provides an introduction to instantiating controls at runtime and exception handling in Delphi. It demonstrates how to dynamically create buttons, labels, and edits during runtime and assign click events to them. It also shows how to use try/except blocks to gracefully handle exceptions, such as preventing runtime errors from invalid pointer references. The document concludes by introducing Delphi console applications as an option for testing code outside of forms.

1. Intro to Event-driven Programming
and Forms with Delphi
L08 - Instantiate Controls at Runtime
Part 2 and other things you need to
know
Mohammad Shaker
mohammadshakergtr.wordpress.com
Intro to Event-driven Programming and Forms with Delphi
@ZGTRShaker
2010, 2011, 2012

3. Instantiate Controls at
Runtime

4. Instantiate Controls at Runtime
• Let’s look at the “OnClickButton”
procedure TForm2.Button1Click(Sender: TObject);
begin
end;

5. Instantiate Controls at Runtime

6. Instantiate Controls at Runtime
• Can we Create Our Own “OnClick” Event?
– YES Sure we can
– But watch out for defining the exact function header as original one
procedure TForm2.ZGTRClick(Sender: TObject);
Begin
End;
Write it yourself

7. Instantiate Controls at Runtime
• Let’s have the following Form

8. Instantiate Controls at Runtime
• And let’s have the following hand-made Event :D
procedure TForm2.ZGTRClick(Sender: TObject);
var i: integer;
Begin
ShowMessage('In My Own Event ');
End;

9. Instantiate Controls at Runtime

10. Instantiate Controls at Runtime
procedure TForm2.Button1Click(Sender: TObject);
Var myButton:TButton;
begin
myButton:= TButton.Create(Self);
myButton.Parent:= Panel1;
myButton.Height:= 35;
myButton.Width:= 100;
myButton.Caption:= 'MyCreatedButton';
myButton.OnClick:= ZGTRClick;
// WOW:D
end;

11. Instantiate Controls at Runtime
Before Clicking the
Dynamic Button

12. Instantiate Controls at Runtime
• Cool, right?
After Clicking the
Dynamic Button

13. Instantiate Controls at Runtime
• Another Ex: Let’s Have The following Form

14. Instantiate Controls at Runtime
Var
i: integer;
// Global Variable
procedure TForm2.FormCreate(Sender: TObject);
begin
i:= 0;
// Initialize Variable
end;
procedure TForm2.ZGTRClick(Sender: TObject);
begin
ShowMessage('Am in my own created EVENT (procedure) '
+ Sender.ClassName);
end;

15. Instantiate Controls at Runtime
procedure TForm2.ZGTRClick(Sender: TObject);
begin
ShowMessage('Am in my own created EVENT (procedure) '
+ Sender.ClassName);
end;

16. Instantiate Controls at Runtime
procedure TForm2.Button1Click(Sender: TObject);
Var myButton:TButton;
myLabel:TLabel;
myEdit:TEdit;
begin
myButton:= TButton.Create(Self);
myButton.Parent:= Panel1;
myButton.Height:= 35;
myButton.Width:= 100;
myButton.Caption:= 'MyCreatedButton';
myButton.Top:= i*20;
myButton.OnClick:= ZGTRClick;
i:=i+2;

17. Instantiate Controls at Runtime
myLabel:= TLabel.Create(Self);
myLabel.Parent:= Panel1;
myLabel.Caption:= 'MyCreatedLabel';
myLabel.Top:= i*20;
myLabel.OnClick:= ZGTRClick;
i:=i+2;
myEdit:= TEdit.Create(Self);
myEdit.Parent:= Panel1;
myEdit.Text:= 'MyCreatedEdit';
myEdit.Top:= i*20;
myEdit.OnClick:= ZGTRClick;
end;

18. Instantiate Controls at Runtime
Cool For Now

19. Instantiate Controls at Runtime
Clicking The
Button

20. Instantiate Controls at Runtime
Clicking The
Label

21. Instantiate Controls at Runtime
Clicking The
Edit

22. Instantiate Controls at Runtime
• Another Ex: Let’s have the previous example with the
following form and modified “ZGTRClick” is like this.

23. Instantiate Controls at Runtime
procedure TForm2.ZGTRClick(Sender: TObject);
var i: integer;
Begin
i:=i+1;
End;
procedure TForm2.Button2Click(Sender: TObject);
begin
ShowMessage('i = ' + IntToStr(i));
end;

24. Instantiate Controls at Runtime
• What will happen now when clicking 4 times on any ones of
the 3 controls, and then clicking (Show”i”).

25. Nice Trick :D
• Another Ex:
– Let’s see the following Example

26. Nice Trick :D
var i: integer;
// Global Variable
procedure TForm2.FormCreate(Sender: TObject);
begin
i:= 0;
// Initialize Variable
end;
procedure TForm2.Button1Click(Sender: TObject);
Var myButton:TButton;
begin
i:= i+1;
myButton:= TButton.Create(Self);
myButton.Parent:= Panel1;
myButton.Top:= i*10;
myButton.Left:= 20;
myButton.OnClick:= Button1Click;
end;

27. Nice Trick :D
Clicking “Create”
button two times
After That
Clicking any ones
of created
buttons

28. Array of Objects

29. Array of Objects
• Declaration
X: Array of String;
M: Array of Array of Integer;

30. Array of Objects

31. Array of Objects
• Let’s have the following from design

32. Array of Objects
procedure TForm2.Button1Click(Sender: TObject);
var ButtonArr: Array of TButton;
begin
try
SetLength(ButtonArr,StrToInt(Edit1.Text));
for I:= 0 to StrToInt(Edit1.Text)-1 do
Begin
ButtonArr[i]:= TButton.Create(Self);
ButtonArr[i].Parent:= Panel1;
ButtonArr[i].Top:= i*30;
ButtonArr[i].Left:= 10;
End;
except
on e: Exception do
ShowMessage('Re-Enter an Integer value.');
end;
end;

33. Array of Objects
• Controls created at Runtime!

35. Exception Handling
• Let’s have the following Example

36. Exception Handling
procedure TForm2.Button1Click(Sender: TObject);
var Ptr: ^Integer;
begin
new(Ptr);
Edit1.Text:= IntToStr(Ptr^);
Ptr^:= 3;
Edit1.Text:= IntToStr(Ptr^);
end;

37. Exception Handling
procedure TForm2.Button1Click(Sender: TObject);
var Ptr: ^Integer;
begin
Edit1.Text:= IntToStr(Ptr^);
Ptr^:= 3;
// Here’s The Error
Edit1.Text:= IntToStr(Ptr^);
end;
Runtime
Error

38. Exception Handling
procedure TForm2.Button1Click(Sender: TObject);
var Ptr: ^Integer;
begin
Edit1.Text:= IntToStr(Ptr^);
end;
No Runtime
Error

39. Exception Handling
the concept

40. Exception Handling
• The structure of exception handling
try
// Code which may raise an exception.
except
on e:Exception do
begin
// Handle exception “e”
end;
finally
// Code which will be executed whether or not an exception is caught
end;

41. Exception Handling
procedure TForm2.Button1Click(Sender: TObject);
var Ptr: ^Integer;
i: integer;
begin
try
// Note that there’s no need for Begin-End In try Statement
Edit1.Text:= IntToStr(Ptr^);
Ptr^:= 3;
Edit1.Text:= IntToStr(Ptr^);
except
on e: Exception do
ShowMessage('Go away , my program is right
, ente el ajdab:D');
end;
end;
No bugs in my code:@

42. Exception Handling

43. Exception Handling
• No Msg
procedure TForm2.Button1Click(Sender: TObject);
var Ptr: ^Integer;
i: integer;
begin
try
Edit1.Text:= IntToStr(Ptr^);
except
on e: Exception do
ShowMessage('Go away , my program is right No bugs in my code:@
, ente el ajdab:D');
end;
end;

44. Exception Handling
• No Msg
procedure TForm2.Button1Click(Sender: TObject);
var Ptr: ^Integer;
i: integer;
begin
try
i:= Ptr^;
except
on e: Exception do
ShowMessage('Go away , my program is right No bugs in my code:@
, ente el ajdab:D');
end;
end;

45. Exception Handling
• Cool!
procedure TForm2.Button1Click(Sender: TObject);
var i: integer;
begin
try
i:= StrToInt(Edit1.Text);
except
on e: Exception do
ShowMessage(‘ Re-Enter Integer value. ‘);
end;
end;

46. Delphi Console Application
Can be used for testing, checking algorithms, tracking
variables before deploying your project into forms.

47. Delphi Console Application

48. Delphi Console Application

49. Delphi Console Application

50. Delphi Console Application
program Project2;
{$APPTYPE CONSOLE}
uses
SysUtils;
begin
try
{ TODO -oUser -cConsole Main: Insert code here }
except
on E:Exception do
Writeln(E.Classname, ': ', E.Message);
end;
end.

51. Delphi Console Application
program Project2;
{$APPTYPE CONSOLE}
uses
SysUtils;
Var
x:integer;
begin
try
{ TODO -oUser -cConsole Main: Insert code here }
except
on E:Exception do
Writeln(E.Classname, ': ', E.Message);
end;
Readln(x);
Writeln('x = ', x);
Readln;
end.

52. Delphi Console Application

54. And.. end of course

55. mohammadshakergtr@gmail.com
http://mohammadshakergtr.wordpress.com/
tweet @ZGTRShaker

57. See you!