[Tcl-bugs] [ tktoolkit-Bugs-2844964 ] (also tcl 2844962) Tcl_UpdateLinkedVar doesn't trigger widge

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Bugs item #2844964, was opened at 2009-08-26 10:33
Message generated for change (Tracker Item Submitted) made by kchansen
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Category: 03. [*button] and [label]
Group: current: 8.6b1
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Karl C. Hansen (kchansen)
Assigned to: Jeffrey Hobbs (hobbs)
Summary: (also tcl 2844962) Tcl_UpdateLinkedVar doesn't trigger widge

Initial Comment:
Also tested in 8.5.7, same behavior.
Also tried ENTRY widgets

OS Platform & Version WinXP with SP3

Problem Behavior
Updates to linked C variables do not trigger widget updates.

If I update a Tcl variable that is tied to a widget, the widget is
automatically updated, presumably via hooks similar to the trace mechanism.
Unfortunately, this does not seem to occur if the variables are tied to C
variables. Calling Tcl_UpdateLinkedVar() *does* update the Tcl-side, since
the following proc demonstrates the updates are occurring by displaying the
Tcl-side values every two seconds when called via "Update 2000":

proc Update {interval} {
if {$::Thresh} {
puts "***************************************************************"
puts "Red: $::RMax"
puts "Green: $::GMax"
puts "Blue: $::BMax"
puts "Interval $interval"
update
}
after $interval "Update $interval"
}

Even though the Tcl variables reflect the updates, the widget values DO NOT
refresh until I manipulate the widget window (e.g. resize).

Below are the pertinent code snippets. I originally tried defining
R/G/BMax as longs, and using them directly, but it occurred to me that
perhaps the update needed to have string variables since the widgets use
"-textvariable" options. Changing the code to the below code had the same
behavior. I also tried calling Tcl_InvalidateStringRep() in the same C
routine which calls Tcl_UpdateLinkedVar() with no changes to behavior.

***tcl***
label .v2.lrmax.rMax -textvariable ::RMax
label .v2.lgmax.gMax -textvariable ::GMax
label .v2.lbmax.bMax -textvariable ::BMax

***init***
sRMax = Tcl_Alloc(256);
sGMax = Tcl_Alloc(256);
sBMax = Tcl_Alloc(256);
Tcl_LinkVar(theInterp, "::RMax", (char *) &sRMax,
TCL_LINK_STRING | TCL_LINK_READ_ONLY);
Tcl_LinkVar(theInterp, "::GMax", (char *) &sGMax,
TCL_LINK_STRING | TCL_LINK_READ_ONLY);
Tcl_LinkVar(theInterp, "::BMax", (char *) &sBMax,
TCL_LINK_STRING | TCL_LINK_READ_ONLY);

***update***
sprintf(sRMax, "%lu", RMax);
Tcl_UpdateLinkedVar(mainInterp, "::RMax");
sprintf(sGMax, "%lu", GMax);
Tcl_UpdateLinkedVar(mainInterp, "::GMax");
sprintf(sBMax, "%lu", BMax);
Tcl_UpdateLinkedVar(mainInterp, "::BMax");


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