Delphi RTTI SetValue for Enumerations

Question

How do I use RTTI to set an enumerated field's value ?

I.e.

type
  TCPIFileStatus= (fsUnknown, fsProcessed);
  TTest = class
    FStatus: TCPIFileStatus; 
  end;
      ...
  var
    Data: TTest;
    Ctx: TRttiContext;
    Status : TCPIFileStatus;
  begin
    Data := TTest.Create;
    Status := fsProcessed;
    Ctx.GetType(Data.ClassType).GetField('FStatus').SetValue(Data, Status);
  end;

I get "Invalid class typecast."
NB:I need to use RTTI because I will not always know the object type or field name at design time.

Answer 1

you must pass a TValue to the SetValue method try using this code :

{$APPTYPE CONSOLE}
uses
  Rtti,
  SysUtils;


type
  TCPIFileStatus= (fsUnknown, fsProcessed);
  TTest = class
    FStatus: TCPIFileStatus;
  end;

  var
    Data   : TTest;
    Ctx    : TRttiContext;
    Status : TCPIFileStatus;
    v      : TValue;
begin
  try
    Data := TTest.Create;
    try
      Status := fsProcessed;
      v:= v.From(status); 
      Ctx.GetType(Data.ClassType).GetField('FStatus').SetValue(Data, v);

      // do your stuff
    finally
       Data.Free;
    end;
  except
    on E: Exception do
      Writeln(E.ClassName, ': ', E.Message);
  end;
end.

Answer 2

Another solution to this problem, in the case you don't know the exact enum type on your function but instead it's TypeInfo, is to use TValue's Make procedure.

procedure Make(AValue: NativeInt; ATypeInfo: PTypeInfo; out Result: TValue); overload; static;

Here is an example (From an XML config parser): This is later used for a TRTTIField/TRTTIProperty.SetValue()

function EnumNameToTValue(Name: string; EnumType: PTypeInfo): TValue;
var
  V: integer;

begin
  V:= GetEnumValue(EnumType, Name);
  TValue.Make(V, EnumType, Result);
end;

Hope this helps you.