Lazarus Hacks

Add here your hacks/modifications to the Lazarus IDE or LCL widgets. If a good idea arises and is good enough it may become part of the official distribution; if not it can be used by other people that need more handy functionality than standards.

  Note: Please post a patch to the bugtracker to get improvements into the Lazarus code. Just posting them here will not work.

Exposing/Extending TCustomEdit

In some applications we need to constantly convert the Text property of TCustomEdit descendants from or to numeric values:

  TCustomEditFilters = (cefNone, cefInteger, cefUnsigned, cefCurrency, cefFloat);

  { TCustomEdit }

  TCustomEdit = class(TWinControl)
  private
    ...
    FTmpModified : Boolean;
    FceFilter : TCustomEditFilters;
    procedure SetceFilter(aCeFilter: TCustomEditFilters);
    function GetAsInteger:Integer;
    procedure SetAsInteger(aVal: Integer);
    function GetAsFloat:Extended;
    procedure SetAsFloat(aVal: Extended);
    function GetAsCurrency:Currency;
    procedure SetAsCurrency(aVal: Currency);

  public
    ...
    property TmpModified: Boolean read FTmpModified write FTmpModified;
    property AsInteger: Integer read getAsInteger write setAsInteger;
    property AsFloat: Extended read getAsFloat write setAsFloat;
    property AsCurrency: Currency read getAsCurrency write setAsCurrency;
  published
    property Alignment: TAlignment read FAlignment write SetAlignment default taLeftJustify;
    property ceFilter : TCustomEditFilters read FceFilter write SetceFilter default cefNone;
  end;

//On the implementation part tcustomedit.inc:

  resourcestring
    rsInvalidNumbe = 'Invalid number !';

  procedure TCustomEdit.Change;
  begin
    FTmpModified := True;
    if Assigned(FOnChange) then FOnChange(Self);
  end;

  procedure TCustomEdit.DoExit;
  begin
    if FCeFilter <> cefNone then
    begin
      case FCeFilter of
        cefInteger, cefUnsigned: AsInteger;
        cefFloat: AsFloat;
        cefCurrency: AsCurrency;
      end;
    end;
    FAutoSelected := False;
    inherited DoExit;
  end;

  procedure TCustomEdit.SetceFilter(aCeFilter: TCustomEditFilters);
  begin
    FCeFilter := aCeFilter;
    if FCeFilter = cefNone then Alignment := taLeftJustify
    else Alignment := taRightJustify;
  end;

  function TCustomEdit.GetAsInteger:Integer;
  begin
    TryStrToInt(Text, result);
  end;

  procedure TCustomEdit.SetAsInteger(aVal: Integer);
  begin
     Text := IntToStr(aVal);
  end;

  function TCustomEdit.GetAsFloat:Extended;
  begin
    if Text = '' then result := 0
    else if not TryStrToFloat(Text, result) then
      Raise Exception.Create(rsInvalidNumbe);
  end;

  procedure TCustomEdit.SetAsFloat(aVal: Extended);
  begin
     Text := FloatToStr(aVal);
  end;

  function TCustomEdit.GetAsCurrency:Currency;
  begin
    if Text = '' then result := 0
    else if not TryStrToCurr(Text, result) then
      raise Exception.Create(rsInvalidNumbe);
  end;

  procedure TCustomEdit.SetAsCurrency(aVal: Currency);
  begin
     Text := CurrToStr(aVal);
  end;

Replacing VK_DECIMAL keypad dot by comma

When writing Lazarus applications to non-US locales there is a problem with the keypad "." (dot) when the locale uses "," (comma) as decimal separator. I've been looking for a solution and ended up with this:

Form.KeyPreview := True; Form.OnKeyDown := @FormKeyDown; Form.OnKeyPress := @FormKeyPress;

  { TFormBase }

  TFormBase = class(TForm)
    ...
  protected
    { protected declarations }
    fVK_Decimal : Boolean;
    ...
  end;

procedure TFormBase.FormKeyPress(Sender: TObject; var Key: char);
begin
   if fVK_Decimal and (key = '.') then key := DecimalSeparator;
end;

procedure TFormBase.FormKeyDown(Sender: TObject; var Key: word; Shift: TShiftState);
begin
  if (Shift = []) and (key = VK_DECIMAL) then
    fVK_Decimal := True; 
end;

See also

• Creating A Patch - How to get your modifications into the Lazarus codebase