OnChange Event For TLabel ??

[Weitentaaal]

Hey Guys,

is there Any Way to Reproduce the On Change Event like the 1 TEdit has ?

Should Be like this :

Function WhenLabelXXChanged
do begin
   Code
end;

There is only OnChangeBounds But that is not what i was Looking For. :/

[Handoko]

TLabel is not supposed to change. Why don't just use a TEdit? Any reason?

[wp]

Since the user cannot enter text in a label any change of the label caption occurs under control of your code where you can react.

If you - for whatever reason - nevertheless absolutely need an OnChange event you must write a specialized Label component. Every TLabel has a protected TextChanged method which you can override to fire an OnChange event handler:

Code: Pascal  [Select][+][-]

1. type
2.   TNewLabel = class(TLabel)
3.     private
4.       FOnChange: TNotifyEvent;
5.     protected
6.       procedure TextChanged; override;
7.     public
8.       property OnChange: TNotifyEvent read FOnChange write FOnChange;
9.     end;  
10.  
11. procedure TNewLabel.TextChanged;
12. begin
13.   inherited;
14.   if Assigned(FOnChange) then FOnChange(self);
15. end;

Since this feature probably is needed only for a few labels I'd replace these labels on the fly by the new label.

Code: Pascal  [Select][+][-]

1. procedure TForm1.FormCreate(Sender: TObject);
2. var
3.   Lbl: TNewLabel;
4. begin
5.   Lbl := TNewLabel.Create(Self);
6.   Lbl.Parent := Label1.Parent;
7.   Lbl.CloneLabel(Label1);
8.   Lbl.OnChange := @<your event handler for the OnChange event of the new label>
9.   Label1.Free;    // Destroy the old label
10.   Label1 := Lbl;  // and replace by the new one
11. end;

The method CloneLabel saves some typing if there are several labels to be replaced:

Code: Pascal  [Select][+][-]

1. procedure TNewLabel.CloneLabel(ALabel: TLabel);
2. begin
3.   Parent := ALabel.Parent;
4.   SetBounds(ALabel.Left, ALabel.Top, ALabel.Width, ALabel.Height);
5.   Caption := ALabel.Caption;
6.   AutoSize := ALabel.AutoSize;
7.   Font := ALabel.Font;
8.   // plus any more properties that you change from default...
9. end;  

See the attached project.

[Weitentaaal]

Thanks A Lot

I need it because as u said "User can't write into it"

I Have A ComboBox with produkts and if u Change Produkts then the Value of the displayed Labael changes

[lucamar]

I need it because as u said "User can't write into it"

I Have A ComboBox with produkts and if u Change Produkts then the Value of the displayed Labael changes

Even so, it must be your own code who changes the label, maybe something like:

Code: Pascal  [Select][+][-]

1. SomeLabel.Caption := ComboBox.Items[ComboBox.ItemIndex]

You can, then, add a proc/function which you can call for example as:

Code: Pascal  [Select][+][-]

1. ...
2. SomeLabel.Caption := ComboBox.Items[ComboBox.ItemIndex]
3. ALabelChanged(SomeLabel);
4. ...

There is no need to sub-class TLabel. Unless you're doing something else, of course ...