Prevent editing in a TComboBoxEx..

[Ian Branch 127]

Hi Team,

I need to prevent Users from actually editing, including deleting, a TComboBoxEx whilst still allowing the contents to be changed via the drop-down.

The component's OnChange event fires whenever they do something in the field.

The component doesn't have a Read-Only property.  This might get in the road of the drop-down working, so what do I do?

 

Regards & TIA,

Ian

 

[Guest]

try this my sample: THIS WORKS BETTER!

procedure TForm1.ComboBoxEx1KeyPress(Sender: TObject; var Key: Char);
begin
  if not(Key = #0) then // if any char was typed by user!
    Key := #0; // imiting "Read-Only" effect!
end;

procedure TForm1.ComboBoxEx1KeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
begin
  if not(Key = 0) then // to keys like DEL...
    Key := 0;
end;

Another Observations:

• when user use "CLICK Mouse", then, "OnClick" is raised
• for all changes, "OnBeginEdit" and "OnEndEdit" is raised any way
• then, you can use a "var" for to knows raise your changes, for example!
• another keys, like "DEL", "BackSpace" can fail  in test (if not lWhoStartEditWasClick then  or If Key='') - it's necessary more verification!

 

some like this:  (BUT IT FAILS IF THE VAR GOES TO = TRUE ALWAYS)  - RE-EDITED

 

var
  Form1: TForm1;

implementation

{$R *.dfm}

var
  lWhoStartEditWasClick: boolean; // false

procedure TForm1.ComboBoxEx1BeginEdit(Sender: TObject);
begin
  Memo1.Lines.Add('beginedit ' + datetimetostr(now));
  lWhoStartEditWasClick := false;
end;

procedure TForm1.ComboBoxEx1Change(Sender: TObject);
begin
  Memo1.Lines.Add('Change ' + datetimetostr(now));
  lWhoStartEditWasClick := false; // forcing new avaliation!
end;

procedure TForm1.ComboBoxEx1Click(Sender: TObject);
begin
  Memo1.Lines.Add('Click ' + datetimetostr(now));
  lWhoStartEditWasClick := true;
end;

procedure TForm1.ComboBoxEx1EndEdit(Sender: TObject);
begin
  Memo1.Lines.Add('endedit ' + datetimetostr(now));
end;

procedure TForm1.ComboBoxEx1KeyDown(Sender: TObject; var Key: Word; Shift: TShiftState);
begin
  if not(Key = 0) then  // keys as DEL
    Key := 0;
end;

procedure TForm1.ComboBoxEx1KeyPress(Sender: TObject; var Key: Char);
begin
  //if not(Key = #0) then // chars
  if not lWhoStartEditWasClick then
    Key := #0;
  //

end;

end.

 

hut

Edited December 6, 2020 by Guest

[Ian Branch 127]

Hi Emailx45,

Oh, that is excellent!  Thank you.

I do like the added logging functionality.

I am going to save that as a code snippet for the future.

 

Regards,

Ian

[Guest]

look again my observation!

[Ian Branch 127]

I did read them and they were noted.

FYI - This is what I now have in place..

procedure TCustomersForm.IndexOrdKeyPress(Sender: TObject; var Key: Char);
begin
  if not(Key = '') then // if any char was typed by user!
  begin
    MessageBeep(MB_ICONERROR);
    TaskMessageDlg('Editing not permitted!', 'You are not permitted to edit this entry.  Please select from the drop-down options!', mtError, [mbOK], 0);
    IndexOrd.Text := 'Customer #';
    Key := #0; // imiting "Read-Only" effect!
    end;
end;

Regards & Tks again,

Ian

Edited December 6, 2020 by Ian Branch

[Guest]

look again about the use of "key" as DEL, BackSpace ...

try never use Dialogs on Events like this!!! you can have a effect non-desired and crash your apps

Edited December 6, 2020 by Guest

[Ian Branch 127]

I saw the observation about the DEL/Backspace, I am prepared to accept the risk att.

OK.  Noted on not using dialogs in this case.  Unfortunate.  I will revise.

[Guest]

for hints, use "Hint / ShowHits" properties

[Ian Branch 127]

100% agree, but in this case the Customer's Users are not the quickest and unless something is in their face, it doesn't get much attention/credence. 😞

[Lajos Juhász 293]

I would just set the property Style to csExDropDownList.

 

[Guest]

13 hours ago, Lajos Juhász said:

I would just set the property Style to csExDropDownList.

 

who dont read all options, dont see it!!!   

It's a shame by me! Sorry!  

... uhhhhhh, shame on the moon!.... by Bob Seager!

 

[Ian Branch 127]

No shame involved.  I suspect ALL programmers are guilty of this more than once.  ;-)