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Display Items
Advantages of Display Items
It is easy to see the advantages of seperating the display items from their
host widgets. First, the display items are easy to learn. Since they are
the same across different types of widgets. Once you learn about a type
of display items, you will know how to use them in all Tix widgets that
support display items (currently these include TixHList, TixTList and the
spreadsheet widget TixGrid, but the number is growing). In contrast, if
you want to create a text item for the Tk widgets, you will find out that
the listbox, text, canvas and entry widget each have a different method
of creating and manipulating text items, and it is quite annoying to
learn each of them individually.
Second, the hosts widgets that use display items are extensible.
Because of the separation of task, the host widgets are not involved
in the implementation details of the display items. Therefore, if
you add a new type of display items, such as a
animation
type
that displays live video, the host widgets will gladly take them in
and display them. You don't need to modify the existing host widgets
at all. In contrast, if you want to display graphical images in the
existing Tk listbox widgets, you'd better set aside 100 hours to
rewrite it completely!
Third, display items are good for writers of host widgets. Because
now they just need to implement the arrangement policy of the host
widgets. They don't need to worry about drawing at all because it is
all handled by the display items. This is a significant saving in
code because a widget that does not use display items has to spend
30%of its C code to do the drawing.
http://tix.sourceforge.net
http://tix.sourceforge.net
