gco function not working (as expected)

I have the following (simplified) code I wrote which is supposed to select n points (of type 'line') on a figure and delete them

for i_inc = 1:n
    while(~(strcmpi(get(gco,'type'),'line')))
    end                                         %%Loops until a line is selected
    h_parent = get(gco, 'Parent');              %%Parent is of type 'Axes'
    h_current = get(gco);
    gco(h_parent);                              %%Set handle to parent so gco type is no longer 'line'
    delete(h_current);
end

The problem is when I call the GCO function, the gco handle does not change. I can change the GCO manually by clicking on different items in a figure, but this defeats the purpose of what the 'gco' function is supposed to do.

Any suggestions?

Answer 1

[Walter Roberson]

You are not using pause() or waitfor() or uiwait() or drawnow() in your while loop, so no graphics interrupts will happen in your loop and the callback object will not get updated.

    gco(h_parent);                              %%Set handle to parent so gco type is no longer 'line'

"gco(figure_handle) returns the handle of the current object in the figure specified by figure_handle"

Calling gco and passing in a parameter does not activate the object that you pass in: the parameter just gives you a way to inquire about an object other than the current figure.

http://www.mathworks.com/help/matlab/ref/gco.html

"The current object is the last object clicked or selected via keyboard interaction, excluding uimenus."

There is no documented way of giving that "last clicked or selected via keyboard interaction" away. The closest to that is the use of Java Robot to fake a click or keypress for you.

On the other hand, in practice you can set() the figure CurrentObject property and that affects gco

[Jeff Wood]

As I mentioned it was a simplified listing (which I left out the pause.

The complete listing is at https://raw.githubusercontent.com/WoodMath/thesis_matlab/master/StereoPoints/fnMenuDelete.m

Anyway it doesn't seem to be an issue anymore.