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{alias:qtrace}
h2. Name
*qtrace* — connect widget and Tcl variable
h2. Syntax
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*qtrace* \[_widget_] _variable_
{panel}
h2. Description
The *qtrace* command assigns a trace variable to a widget. A trace variable will at all times reflect the state or contents of the widget to which it is assigned. Writing to the variable will update the widget accordingly.
{note}
Assigning a value to a trace-variable may result in the corresponding widgets callback function being called. Use [qblockedtrace] to create a trace variable without this effect.
{note}
h2. Arguments
_widget_
{indent}The widget to which the variable will be connected. If this argument is omitted the current widget will be used. This must be an instance of [QLineEdit], [QLabel], [QTextEdit], [QTextEdit, [QCheckBox], [QRadioButton], [QSpinBox], [QDoubleSpinBox], [QHSlider], and [QVSlider].
{indent}]
_variable_
{indent}The name of the variable. The variable should be global or exist in a namespace. When referring to a namespace variable the namespace name should be part of the argument, like "MyNamespace::my_variable".
{indent}
h2. Examples
h3. Ex.1: QTrace
{anchor:QTrace}
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Name
qtrace — connect widget and Tcl variable
Syntax
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qtrace [widget] variable |
Description
The qtrace command assigns a trace variable to a widget. A trace variable will at all times reflect the state or contents of the widget to which it is assigned. Writing to the variable will update the widget accordingly.
| Note |
|---|
Assigning a value to a trace-variable may result in the corresponding widgets callback function being called. Use qblockedtrace to create a trace variable without this effect. |
Arguments
widget
]
variable
Examples
Ex.1: QTrace
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set w [qwidget ]
qsetwindowtitle "Variable tracing"
# Create text editor and "Show Text" button.
set layout [qhboxlayout $w]
set label [qlabel "First Name :"]
qaddwidget $layout $label
set lineedit [qlineedit]
qaddwidget $layout $lineedit
# Connect contents of line edit to variable 'name'
qtrace $lineedit name
# Set Tcl variable - this will automatically set the
# text in the line edit to 'Jon'
set name Jon
qshow $w
{noformat}
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The
...
above
...
example
...
attaches
...
the
...
variable
...
'name'
...
to
...
the
...
lineedit
...
for
...
entering
...
a
...
persons
...
name.
...
Throughout
...
the
...
execution
...
of
...
the
...
program
...
these
...
entities
...
will
...
keep
...
one
...
another
...
automatically
...
updated.
...
When
...
the
...
variable
...
'name'
...
is
...
assigned
...
the
...
name
...
"Jon",
...
the
...
lineedit
...
is
...
updated
...
accordingly.
...
This
...
can
...
be
...
seen
...
in
...
the
...
screenshot.
...
Also,
...
if
...
the
...
user
...
were
...
to
...
edit
...
the
...
lineedit
...
directly,
...
the
...
'name'
...
variable
...
would
...
be
...
updated
...
accordingly.
...