How to write property in the pascal language?
lazarus / 13-General

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tpglemur · 2008-10-02 12:51

At the code below, when I set MyText.Text:='Hello World' at the
Button1Click, nothing happens. I expected SetMyText to fire.

I know if I had a GetMyText procedure, Setting the Text parameter in
MyText will call it, but how do I tell the difference between when
it's being called. eg MyText.Text:='Hello World' or
Edit1.Text:=MyText.Text

Code: [Select]
  TForm1 = class(TForm)
    Button1: TButton;
    Edit1: TEdit;
    procedure Button1Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    FMyText: TStringList;
  protected
    procedure SetMyText(Value: TStringList);
  public
    property MyText: TStringList read FMyText write SetMyText;
  end;

var
  Form1: TForm1;

implementation

{ TForm1 }

procedure TForm1.FormCreate(Sender: TObject);
begin
  FMyText := TStringList.Create;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  FMyText.Free;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  MyText.Text:='Hello World';
end;

procedure TForm1.SetMyText(Value: TStringList);
begin
  If (Value <> nil) then FMyText.Assign(Value);
  Edit1.Text:=FMyText.Text;
end;   


Hope someone can help.

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theo · 2008-10-02 23:07

Why do you expect SetMyText to fire?
MyText.Text:='Hello World' is _reading_  FMyText and then setting the
property "Text" of this object (TStringList).
SetMyText would "fire" if you did this:
MyText:=MyOtherStringList;

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tpglemur · 2008-10-03 05:09

Thanks for your reply, but, how then do I detect a text change? I
can't expect the user to create a stringlist everytime he wants to
change the text.

I notice TStringList has an OnChange property, can this somehow be
used?

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theo · 2008-10-03 09:25

I have no idea what you are trying to achieve.
Why do you need a Stringlist at all?

http://www.catb.org/~esr/faqs/smart-questions.html#goal

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Leledumbo · 2008-10-04 08:46

I agree with theo. Seeing your code, String should be enough.