Assigning a value to a number field through a button

Question

11gxe , apex 4.x ,
hi all ,
i am trying to assign value to a number field through a button ,
i created a button , then a dynamic action for this button , when it is clicked ,
the dynamic action is based on Pl\Sql code , and the code is
begin
:p2_assign := 455 ; -- where the page is "p2" and the number field is "assign"
end ;
but it does not work , why ?

Answer 1

I can see the toolbar now from the last link you provided me with ,
but you showed me the way to use the static assigning , and assigning with sql , and i want to do it with "Pl\Sql"
in order to know why my way of writing the code does not work , although it is written properly , and should work .
every input item is a variable , and i am doing so
begin 
:p2_assign := 455 ; -- where the page is "p2" and the number field is "assign" 
end ;
to assign a value to a variable ,
and
doing this
begin 
select 455 into :p2_no from dual ; 
end ;  
to select a value into a variable , then
why does not it work ??
and how to do it with pl\sql ?
thanks