Datawindow field : accept only positive numbers

Question

I want to make a datawindow field accept only positive numbers. How can I do that?

Edit

I know I can validate the column using column specification's validation expression system. But is there any format available which I can put into the Format property and be done with it?

Answer 1

No, the simple solution is a validation rule but a more complicated solution to really filter the key pressed is possible.

First you map a userevent (ue_nonnegative) to the datawindow control event pbm_dwnkey.

double ld_value
long  ll_row

if this.getcolumnname() = "value" then
    if key = KeySubtract! or key = KeyDash! then
         ll_row = this.GetRow()
         ld_value = this.getitemnumber(ll_row, "value")
        yield() 
         post event ue_filtervalue(ll_row, ld_value)
    else
        yield() 
        accepttext()
    end if
end if

Here the datawindow has a column named value. I check if the "-" is pressed, if yes I keep the current value and a new event ue_filtervalue is posted. A yield() is necessary to make sure that the ue_filtervalue event will happen after the remaining datawindow event.

The ue_filtervalue event will restore the previous value without the "-".

this.setitem(ad_row, "value", ad_value)
this.SelectText( Len( String(ad_value)) + 1, Len( String(ad_value)) )

Answer 2

If you use an editmask that begins with + it will only accept positive values. The plus sign displays, which you may find undesirable.