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delayed evaluation for tk callbacks?

Posted by that_guy (that_guy), 8 August 2003
Hello.  I remember seeing a really useful post by Graham describing common mistakes made when dealing with delayed evaluation for Tk callbacks/ widget variables. I can't seem to find this post, so if anyone has  a link to it, I'd greatly appreciate it.  The question behind all this: is it possible to have the -textvariable of a widget be set to a delayed evaluation of a command? In this case that command would be a database query. In other words something like :
label .lbl -textvariable "{mysqlsel db "select ip_addr from hosts where host='$::host'}"    I'm not entirely sure how Tk's tracing works- but I'm guessing that  my question makes no sense because it
would cause the label to make countless database queries... and that instead I need to make sure that all methods modifying the database reflect their actions in a variable exposed to the widget.

Posted by admin (Graham Ellis), 10 August 2003
Graham answering briefly - I'm away from my office for a few days so I'll struggle to find it just like you.

Couple of tips:

1. You *can* do a -command as well as a -textvariable, so you can change a variable and run a proc when an interactive widget is changed.

2.  Note update idletasks if you want you display updated even if you haven't finished handling all events.

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