Delphi RTTI: Get property's class

Question

Using Delphi 2010 and RTTI, I know how to get the class type of an object and how to get/set the value and type of an object's properties, but how do you determine which class in the inheritance chain a property came from? I want to use the properties of a base class differently than the main class.

Consider this code:

TClassBase = class(TObject)
published
  property A: Integer;
end;

TClassDescendant = class(TClassBase)
published
  property B: Integer;
end;

procedure CheckProperties(Obj: TObject);
var
  ctx: TRttiContext;
  objType: TRttiType;
  Prop: TRttiProperty;
begin
  ctx := TRttiContext.Create;
  objType := ctx.GetType(Obj.ClassInfo);
  for Prop in objType.GetProperties do begin
    if Prop.GetClassType is TClassBase then
      // do something special with base class properties
    else
      // standard functionality on all other properties
  end;
end;

The problem is there is no GetClassType for the properties. ClassType just returns TRttiInstancePropertyEx instead of the name of the class to which the property belongs.

Answer 1

You can use the GetDeclaredProperties method to get properties declarated in the current class and then compare against the values returned by the GetProperties method.

Try this sample.

{$APPTYPE CONSOLE}

{$R *.res}

uses
  Rtti,
  SysUtils;

type
  TClassBase = class(TObject)
    private
      FA: Integer;
   published
    property A: Integer read FA;
  end;

  TClassDescendant = class(TClassBase)
    private
      FB: Integer;
    published
    property B: Integer read FB;
  end;

procedure CheckProperties(Obj: TObject);

  function ExistProp(const PropName:string; List:TArray<TRttiProperty>) : Boolean;
  var
   Prop: TRttiProperty;
  begin
   result:=False;
    for Prop in List do
     if SameText(PropName, Prop.Name) then
     begin
       Result:=True;
       break;
     end;
  end;

var
  ctx: TRttiContext;
  objType: TRttiType;
  Prop: TRttiProperty;
  CurrentClassProps : TArray<TRttiProperty>;
begin
  ctx := TRttiContext.Create;
  objType := ctx.GetType(Obj.ClassInfo);
  CurrentClassProps:=objType.GetDeclaredProperties;
   for Prop in objType.GetProperties do
   if ExistProp(Prop.Name, CurrentClassProps) then
     Writeln(Format('The property %s is declarated in the current %s class',[Prop.Name, obj.ClassName]))
   else
     Writeln(Format('The property %s is declarated in the base class',[Prop.Name]))
end;



begin
  try
   //CheckProperties(TClassBase.Create);
   CheckProperties(TClassDescendant.Create);
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
  Readln;
end.

Answer 2

I don't know if it's possible to get the class which a property was introduced, but you can solve your problem with regular RTTI:

begin
  ...

  for Prop in objType.GetProperties do begin
    if Assigned(GetPropInfo(TClassBase, Prop.Name)) then
      // do something special with base class properties
    else
      // standard functionality on all other properties
  end;
end;