Question

We know how to program Matlab to do something when a button is clicked, which is this:

    button= uicontrol('Style','pushbutton','String','click me',...
   'Position',[260 80 60 20],...
   'Callback','disp ('' The button is clicked'')');

So the piece of code or function placed after ‘callback’ will be called whenever that button is pressed and released.( so the handler will be called only upon release of the button)

However I wanna be able to activate some code whenever the button is held down and not yet released. How can I do that?

Answer 1

You must use a callback function for the “ButtonDownFcn” property. From here:”

ButtonDownFcn

string or function handle (GUIDE sets this property)

Button-press callback routine. A callback routine that can execute
when you press a mouse button while the pointer is on or near a
uicontrol. Specifically:

If the uicontrol’s Enable property is set to on, the ButtonDownFcn
callback executes when you click the right or left mouse button in a
5-pixel border around the uicontrol or when you click the right mouse
button on the control itself.

If the uicontrol’s Enable property is set to inactive or off, the
ButtonDownFcn executes when you click the right or left mouse button
in the 5-pixel border or on the control itself.

This is useful for implementing actions to interactively modify
control object properties, such as size and position, when they are
clicked on (using selectmoveresize, for example).

Define this routine as a string that is a valid MATLAB expression or
the name of a code file. The expression executes in the MATLAB
workspace.

To add a ButtonDownFcn callback in GUIDE, select View Callbacks from
the Layout Editor View menu, then select ButtonDownFcn. GUIDE sets
this property to the appropriate string and adds the callback to the
code file the next time you save the GUI. Alternatively, you can set
this property to the string %automatic. The next time you save the
GUI, GUIDE sets this property to the appropriate string and adds the
callback to the code file.

Use the Callback property to specify the callback routine that
executes when you activate the enabled uicontrol (e.g., click a push
button).