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Callback functions can be associated with graphics objects and triggered after certain events occur. The basic structure of all callback function is
function mycallback (hsrc, evt) … endfunction
where hsrc
is a handle to the source of the callback, and evt
gives some event specific data.
The function can be provided as a function handle to a plain Octave function, as an anonymous function, or as a string representing an Octave command. The latter syntax is not recommended since syntax errors will only occur when the string is evaluated. See Function Handles section.
This can then be associated with an object either at the object’s creation, or
later with the set
function. For example,
plot (x, "DeleteFcn", @(h, e) disp ("Window Deleted"))
where at the moment that the plot is deleted, the message
"Window Deleted"
will be displayed.
Additional user arguments can be passed to callback functions, and will be passed after the two default arguments. For example:
plot (x, "DeleteFcn", {@mycallback, "1"}) … function mycallback (h, evt, arg1) fprintf ("Closing plot %d\n", arg1); endfunction
Caution: The second argument in callback functions—evt
—is
only partially implemented in the Qt graphics toolkit:
evt
is a class double
value: 1 for left, 2 for middle, and 3 for
right click.
evt
is a structure with fields Key
(string), Character
(string), and Modifier
(cell array of strings).
evt
is a class double
empty matrix.
The basic callback functions that are available for all graphics objects are
CreateFcn
later with the set
function will
never be executed.
By default callback functions are queued (they are executed one after the other
in the event queue) unless the drawnow
, figure
, waitfor
,
getframe
, or pause
functions are used. If an executing callback
invokes one of those functions, it causes Octave to flush the event queue,
which results in the executing callback being interrupted.
It is possible to specify that an object’s callbacks should not be interrupted
by setting the object’s interruptible
property to "off"
. In
this case, Octave decides what to do based on the busyaction
property of
the interrupting callback object:
queue
(the default)The interrupting callback is executed after the executing callback has returned.
cancel
The interrupting callback is discarded.
The interruptible
property has no effect when the interrupting callback
is a deletefcn
, or a figure resizefcn
or closerequestfcn
.
Those callbacks always interrupt the executing callback.
The handle to the object that holds the callback being executed can be
obtained with the gcbo
function. The handle to the ancestor figure
of this object may be obtained using the gcbf
function.
Return a handle to the object whose callback is currently executing.
If no callback is executing, this function returns the empty matrix. This
handle is obtained from the root object property "CallbackObject"
.
When called with a second output argument, return the handle of the figure containing the object whose callback is currently executing. If no callback is executing the second output is also set to the empty matrix.
Return a handle to the figure containing the object whose callback is currently executing.
If no callback is executing, this function returns the empty matrix. The
handle returned by this function is the same as the second output argument
of gcbo
.
Callbacks can equally be added to properties with the addlistener
function described below.
Next: Application-defined Data, Previous: Marker Styles, Up: Advanced Plotting [Contents][Index]