iif - RDLC - Show/hide textbox corresponding value -

i want show textbox field, if value > 0. if field 0 (empty) textbox should hidden (or not visible).

i tried following: -in textbox field (postageandpacking) selected show or hide based on epxression. , entered following expression =iif(string.isnullorempty(fields!postageandpacking.value), true, false)

but received error message: der hidden-ausdruck für das textfeld-objekt 'postageandpacking' verweist auf das feld 'postageandpacking'. ein ausdruck für ein berichtselement kann nur auf felder verweisen, die sich im aktuellen datasetbereich oder, wenn der ausdruck zu einer aggregatfunktion gehört, im angegebenen datasetbereich befinden.

what wrong expression? or have show/hide field corresponding value?

thanks!

the problem fields!postageandpacking.value belongs data set in report , there might many values data set might have many records. question field rows of data set want check expression against.

semantically, data set might have 1 row, still need explicitly request first element this:

=not(string.isnullorempty(first(fields!postageandpacking.value, "dataset1"))) 

assuming here name of data set dataset1, expression show textbox if first postageandpacking of data has value , hide if postageandpacking empty.

note not need use iif since string.isnullorempty() returns boolean.