Using C++Builder to access columns of TIWDBGrid

[Ibouka]

Hi!
I followed this Delphi sample for accessing columns of a TIWDBGrid using C++Builder, but it does not work. 
Below is my code:

Code:

__fastcall TForm1::TForm1(TComponent* Owner) : TFrame(Owner)
{//
 TRESTClient *REST1Client = new TRESTClient(this);
 TRESTRequest *REST1Request = new TRESTRequest(this);
 TRESTResponse *REST1Response = new TRESTResponse(this);
 TClientDataSet *ClientDataSet1 = new TClientDataSet(this);
 TRESTResponseDataSetAdapter *REST1ResponseDataSetAdapter = new TRESTResponseDataSetAdapter(this);

 ClientDataSet1->AfterOpen = &ClientDataSet1AfterOpen;

 REST1Client->BaseURL = "my.URL.php";
 REST1Request->Client = REST1Client;
 REST1Request->Response = REST1Response;
 REST1Response->ContentType = "application/json";
 REST1ResponseDataSetAdapter->Dataset = ClientDataSet1;
 REST1ResponseDataSetAdapter->Response = REST1Response;
 REST1ResponseDataSetAdapter->Active = true;
 REST1Request->Execute();

 TDataSource *DataSource1 = new TDataSource(this);
 DataSource1->DataSet = ClientDataSet1;
 IWDBGrid1->DataSource = DataSource1;

// dynamic_cast<TIWDBGridColumn*>(IWDBGrid1->Columns->Items[0])->Width = (IWDBGrid1->Width/20) * 02; // => Argument out of range
}
//---------------------------------------------------------------------------
void __fastcall TForm1::ClientDataSet1AfterOpen(TDataSet *DataSet)
{//
 dynamic_cast<TIWDBGridColumn*>(IWDBGrid1->Columns->Items[0])->Width = (IWDBGrid1->Width/10) * 2; // => Argument out of range
 dynamic_cast<TIWDBGridColumn*>(IWDBGrid1->Columns->Items[1])->Width = (IWDBGrid1->Width/10) * 1;
 dynamic_cast<TIWDBGridColumn*>(IWDBGrid1->Columns->Items[2])->Width = (IWDBGrid1->Width/10) * 4;
 dynamic_cast<TIWDBGridColumn*>(IWDBGrid1->Columns->Items[3])->Width = (IWDBGrid1->Width/10) * 3;

 dynamic_cast<TIWDBGridColumn*>(IWDBGrid1->Columns->Items[0])->Title->Text = "AFirstTitle";
 dynamic_cast<TIWDBGridColumn*>(IWDBGrid1->Columns->Items[1])->Title->Text = "ASecondTitle";
 dynamic_cast<TIWDBGridColumn*>(IWDBGrid1->Columns->Items[2])->Title->Text = "AThirdTitle";
 dynamic_cast<TIWDBGridColumn*>(IWDBGrid1->Columns->Items[3])->Title->Text = "AFourthTitle";
}
//---------------------------------------------------------------------------
void __fastcall TForm1::IWDBGrid1Render(TObject *Sender)
{//
 // dynamic_cast<TIWDBGridColumn*>(IWDBGrid1->Columns->Items[0])->Width = (IWDBGrid1->Width/10) * 2; // => Argument out of range
}
//---------------------------------------------------------------------------

I am having the error message "Argument out of range" beginning from the first line and for each line.
Any idea of how to get rid of this error?