Function to filter from various fields

Hello,

I would like to build a function which have the parameters filter-field and filter-value.
The need for a page.
This Page has given the SourceTableTemporary property = Yes. The data is parsed when the page is started.
Well I thought I can do it with FieldRef. Unfortunately, I have not worked so far.
I have built the following function AddFilter.

CurrentFieldFilter := FilterField.GETFILTER;
IF STRLEN(CurrentFieldFilter > 0 THEN
  CurrentFieldFilter+= '|';
CurrentFieldFilter+= AddFilterText;
FilterFeld.SETFILTER(CurrentFieldFilter);

MESSAGE('Field-Name: %1 und Filter-Value: %2',FilterField.NAME,CurrentFieldFilter);
MESSAGE('FieldrefFilter : %1',FilterField.GETFILTER);

MESSAGE('%1',GETFILTER(Bodentypgruppe));

CurrPage.UPDATE(FALSE);

and call this function so. However here 'SB' the filter value and should be filtered by the field "Bodentypgruppe".

ABCRecRef.OPEN(DATABASE::"Prod.Planungszeilen");
MyFieldRef := ABCRecRef.FIELD(FIELDNO(Bodentypgruppe));

FilterAdd('SB',MyFieldRef);

The first two message commands provide me with the correct results and the third I get the message that no filter is set to this field.

What´s wrong? Or is this not possible.

thanks
stony