如何在TClientDataSet.CreateDataSet后，代码实现增加一个计算字段？

Question

在如下的代码中，我希望由用户提供的FieldDefs列表动态地生成一个TClientDataSet
，在CreateDataset之前都是成功的，但是在为TClientDataSet增加计算字段时出错，
请问这是为什么，以及如何正确地增加计算字段？
谢谢！！
Type
  TWIField=record
    FldType:TFieldType;
    Size:Integer;
    FldName:String;
    DisplayLabel:String;
    Visible:boolean;
    FldKind:TFieldKind;
  end;
  PWIField=^TWIField;
...............................
...............................procedure CreateDataSet(CDSet:TClientDataSet;FieldDefs:TList);
Var
  i:Integer;
  AFld:TField;
begin
  for i:=0 to FieldDefs.Count-1 do
    if PWIField(FieldDefs.Items[i]).FldKind=fkData then
      With CDSet.FieldDefs.AddFieldDef do
      begin
        DataType:=PWIField(FieldDefs.Items[i]).FldType;
        if DataType=ftString then
          Size:=PWIField(FieldDefs.Items[i]).Size;
        Name:=PWIField(FieldDefs.Items[i]).FldName;
      end;
  if CDSet.FieldDefs.Count>0 then
    CDSet.CreateDataSet;
  ///////////  
 if PWIField(FieldDefs.Items[i]).FldKind=fkCalculated then
    begin
      AFld:=TField.Create(Application);
      AFld.FieldKind:=fkCalculated;
      AFld.FieldName:=PWIField(FieldDefs.Items[i]).FldName;
      if AFld.DataType=ftString then
        AFld.Size:=PWIField(FieldDefs.Items[i]).Size;
      CDSet.Fields.Add(AFld);
    end;
  end;

Answer 1

var
  Field :TIntegerField;
begin
  cds.Close;
  Field := TIntegerField.Create(cds);
  Field.FieldKind := fkCalculated;
  Field.Name := 'cdsc';
  Field.FieldName := 'c';
  Field.DataSet := cds;
  cds.Open;
end;