When the user presses the Enter key in the
self.pageNoEntry field, this
handler is called. If the user has entered a valid integer
that is within the range of external page numbers (counting
from 1), we call the
method to present that page.
Because this handler uses the event binding (
.bind()) rather than the command binding (
command=...), it is called with an
Event object as an argument. However, we don't need
the event to find out what happened. We simply inspect the value
.__pageNoVar control variable and
attempt to use it to change the page number.
If the user enters something other than a number in the
Entry widget, or a number that is
outside the range of page numbers, we could give them an
error popup, but it should be sufficient feedback just to
change the field's value back to the current page number.
# - - - P a g e T u r n e r . _ _ p a g e N o H a n d l e r - - - def __pageNoHandler ( self, event ): """Handle a change to self.pageNoEntry [ event is an Event object -> if self.__pageNoVar contains a valid integer that is in the range [1,len(self.__pageList)] -> self := self displaying int(self.__pageNoVar.get()) else -> self.pageNoEntry := self.__pageNo as a string ] """
First we get the field value, attempt to convert it to an integer, and check that it is a valid external page number. If any of these steps fail, reset the page number and exit.
#-- 1 -- # [ if self.__pageNoVar contains an integer in # [1,len(self.__pageList)] -> # self := self displaying page (pageNo) # return # else -> I ] try: pageNo = int ( self.__pageNoVar.get() ) if ( 1 <= pageNo <= len(self.__pageList) ): self.setPageNo ( pageNo ) return except ValueError: pass #-- 2 -- # [ self.pageNoEntry := self.__pageNo as a string ] self.__pageNoVar.set ( self.__pageNo )