Delphi and dynamic properties

[lang_it]

Linguaggio : Borland Delphi 7

Sistema Operativo : Win Xp Pro

Come premessa a volte è necessario rendere l’applicazione che si stà  sviluppando il più flessibile possibile. Per evitare di avere migliaia di personalizzazioni per migliaia di clienti. Una cosa che può aiutare in questo è la modifica banale di alcune proprietà  dei componenti dell’applicaiozne stessa a runtime in funzione di particolari parametri.

In Delphi è possibile fare questo in modo molto semplice senza dover scrivere granchè di codice, per rendere ancora più semplice la cosa ho preparato una banale applicazione d’esempio scaricabile da :  [download id=”2″]

In particolare tale applicazione :

• mostra come sia possibile maneggiare un Componente (Oggetto) partendo dal nome dello stesso :

Var

Comp : TComponent;

Begin

Comp := FindComponent(cbComponenti.Text);

blablabla .......

• come ottenere l’elenco delle proprietà  e, dei relativi nomi, da un definito componente

procedure TForm1.cbPropertyNameDropDown(Sender: TObject);
var
 Comp : TComponent;
 PropInfo : PPropInfo;
 PropList : PPropList;
 I, PropCount,ListSize : Integer;
begin
 Try
  cbPropertyName.Clear;
  Comp := FindComponent(cbComponenti.Text);
  If Comp = nil then Exit;

  (* ALLOCATING MEMORY FOR THE PROPERTY LIST *)
  PropCount := GetPropList(Comp.ClassInfo,tkAny,nil);
  ListSize  := PropCount * SizeOf(Pointer);
  Getmem(PropList,ListSize);

  PropCount := GetPropList(Comp.ClassInfo,tkAny,PropList,true);
  If not assigned(PropList) then Exit;

  For I:=0 to PropCount -1 do
   begin
    PropInfo := PropList^[I];
    If Assigned(PropInfo) then
     Begin
      if PropInfo^.PropType^.Kind in tkMethods then
       Begin
        // If is an avent handler do something
       end
      Else // if is a property
       Begin
        cbPropertyName.Items.Add(PropInfo^.Name);
       end;
     end;
   end;
  cbPropertyName.Update;
 Finally
  FreeMem(PropList);
 End;

end;

• impostare il valore di una proprietà  partendo dal componente a cui appartiene e dal suo nome

procedure TForm1.btnDoItClick(Sender: TObject);
var
 Comp : TComponent;
 PropInfo : PPropInfo;
begin
  Comp := FindComponent(cbComponenti.Text);
  If Comp <> nil then
   Begin
    PropInfo := GetPropInfo(Comp.ClassInfo,cbPropertyName.Text);
    //SetVariantProp();
    SetPropValue(Comp,cbPropertyName.Text,edPropValue.Text);

    (*
    exit;
    if Assigned(PropInfo) then
     Begin
      case PropInfo^.PropType^.Kind of
         tkInteger       : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkChar          : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkEnumeration   : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkFloat         : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkString        : Begin SetStrProp(Comp,PropInfo,edPropValue.Text) end;
         tkSet           : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkClass         : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkMethod        : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkWChar         : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkLString       : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkWString       : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkVariant       : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkArray         : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkRecord        : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkInterface     : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkInt64         : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkDynArray      : Begin ShowMessage(PropInfo^.PropType^.Name) end;
      end;
     end;
     *)
   End;
end;

[/lang_it]

[lang_en]

Linguaggio : Borland Delphi 7

Sistema Operativo : Win Xp Pro

Sometimes, you need to extend the flexibility of your application, to prevent managinig thousands release of an application for thousands customore.One of the most important feature is the posibility of modify a component property value at runtime.

With Delphi is possible and simple to do like in this demo application: [download id=”2″]

The core features of this demo application are : :

• get an object from his name ,using a string, that can be filled in a ini file or xml or db table :

Var

Comp : TComponent;

Begin

Comp := FindComponent(cbComponenti.Text);

blablabla .......

• obtain the list of properties and published methods/event of the selected object

procedure TForm1.cbPropertyNameDropDown(Sender: TObject);
var
 Comp : TComponent;
 PropInfo : PPropInfo;
 PropList : PPropList;
 I, PropCount,ListSize : Integer;
begin
 Try
  cbPropertyName.Clear;
  Comp := FindComponent(cbComponenti.Text);
  If Comp = nil then Exit;

  (* ALLOCATING MEMORY FOR THE PROPERTY LIST *)
  PropCount := GetPropList(Comp.ClassInfo,tkAny,nil);
  ListSize  := PropCount * SizeOf(Pointer);
  Getmem(PropList,ListSize);

  PropCount := GetPropList(Comp.ClassInfo,tkAny,PropList,true);
  If not assigned(PropList) then Exit;

  For I:=0 to PropCount -1 do
   begin
    PropInfo := PropList^[I];
    If Assigned(PropInfo) then
     Begin
      if PropInfo^.PropType^.Kind in tkMethods then
       Begin
        // If is an avent handler do something
       end
      Else // if is a property
       Begin
        cbPropertyName.Items.Add(PropInfo^.Name);
       end;
     end;
   end;
  cbPropertyName.Update;
 Finally
  FreeMem(PropList);
 End;

end;

• setting the value of a property, for simple we have used SetPropValue , an untyped method that use a variant as parameter to send to selected property of the object

procedure TForm1.btnDoItClick(Sender: TObject);
var
 Comp : TComponent;
 PropInfo : PPropInfo;
begin
  Comp := FindComponent(cbComponenti.Text);
  If Comp <> nil then
   Begin
    PropInfo := GetPropInfo(Comp.ClassInfo,cbPropertyName.Text);
    //SetVariantProp();
    SetPropValue(Comp,cbPropertyName.Text,edPropValue.Text);

    (*
    exit;
    if Assigned(PropInfo) then
     Begin
      case PropInfo^.PropType^.Kind of
         tkInteger       : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkChar          : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkEnumeration   : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkFloat         : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkString        : Begin SetStrProp(Comp,PropInfo,edPropValue.Text) end;
         tkSet           : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkClass         : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkMethod        : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkWChar         : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkLString       : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkWString       : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkVariant       : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkArray         : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkRecord        : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkInterface     : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkInt64         : Begin ShowMessage(PropInfo^.PropType^.Name) end;
         tkDynArray      : Begin ShowMessage(PropInfo^.PropType^.Name) end;
      end;
     end;
     *)
   End;
end;

[/lang_en]