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How to know when a TMemo's control has had text selected?

Posted on 2010-08-25
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Last Modified: 2012-05-10

I am trying to enable/disable a button & menu item based on whether or not a TMemo's text has been selected

I dont see an event that triggers when text is selected...so how can i trap for it?
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Question by:Looking_4_Answers
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11 Comments
 
LVL 17

Expert Comment

by:TheRealLoki
Comment Utility
To know, you just need to check the SelLength property, but I don't know of an event/message off hand
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Author Comment

by:Looking_4_Answers
Comment Utility
ya, i know that part, but i need something that kicks it off
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LVL 32

Expert Comment

by:ewangoya
Comment Utility
Try the  mouse up event

procedure TForm1.Memo1MouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  button1.Enabled := (Sender as TMemo).SelLength;
end;
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Accepted Solution

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ewangoya earned 250 total points
Comment Utility
procedure TForm1.Memo1MouseUp(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  button1.Enabled := (Sender as TMemo).SelLength > 0;
end;
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LVL 36

Expert Comment

by:Geert Gruwez
Comment Utility
whenever something happens in a delphi form a procedure UpdateActions gets called
you can make your own event with that:
type
  TForm1 = class(TForm)
  private
    fSelLength: integer;
    procedure MemoSelLengthChanged(aMemo: TMemo; OldSelLength, NewSelLength: integer);
  protected
    procedure UpdateActions; override;
  public
    constructor Create(AOwner: TComponent); override;  
  end;

constructor TForm1.Create(AOwner: TComponent); 
begin
  inherited Create(AOwner);
  fSelLength := 0;
end;

procedure TForm1.UpdateActions; 
var CurSelLength: Integer;
begin
  inherited UpdateActions;
  CurSelLength := Memo1.SelLength;
  if fSelLength <> CurSelLength then 
  begin
    MemoSelLengthChanged(Memo1, fSelLength, CurSelLength);
    fSelLength := CurSelLength;
  end;
end;

procedure TForm1.MemoSelLengthChanged(aMemo: TMemo; OldSelLength, NewSelLength: integer);
begin
  // Do Your code here  
end;

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LVL 25

Expert Comment

by:epasquier
Comment Utility
Geert : That is excellent. I never thought of the use of UpdateActions in this way.
for information, that is a method introduced in TComponent

I would have used a procedure that is called by keyPressed, Key Up & mouse Up events, so like ewangoya but including all events that can change the selection.

I would need to test how often UpdateActions is called, and if there are cases where the 'mouse&key events' method fails (like if the selection is changed programmatically) before choosing which method I'll keep, but considering that there is not much load in a simple test and a button state change, why not being extensive ?

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LVL 36

Expert Comment

by:Geert Gruwez
Comment Utility
>>epasquier ugh ?
you'r last sentence is not very clear (at least to me, and i haven't had a beer yet ...)

The simplicity of using UpdateActions is somewhat frightening.
It doesn't go very well for debugging, because it get's called very often.
If anybody intends to use this procedure then anything in it must be blazing fast
Don't use any queries in this procedure directly ... it will slow down your delphi app
Maybe i should write a article about UpdateActions ... the ins and outs

I have found that setting enable/visible in this procedure is the easiest to do.
You don't have to provide anything to call this procedure, Delphi does it for you

However if you need to check things like enable/visible which are set in UpdateActions
In the same procedure/function in 2 different places then you may have to call it explicitely.
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LVL 14

Expert Comment

by:systan
Comment Utility
The simpliest;
procedure TForm1.Memo1MouseUp(Sender: TObject; Button: TMouseButton;

  Shift: TShiftState; X, Y: Integer);

begin

if memo1.SelText <> '' then showmessage(memo1.SelText + '  was selected');

end;

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LVL 25

Expert Comment

by:epasquier
Comment Utility
@Geert : Well my last sentence was just expressing concerns about precisely what you said after : it is called too often for big code, but in this case that looks one helluva easy way
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LVL 36

Expert Comment

by:Geert Gruwez
Comment Utility
there goes the effort again ... way too much
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LVL 25

Expert Comment

by:epasquier
Comment Utility
> there goes the effort again ... way too much
???
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