MATLAB: Accessing an actxserver COM object with a GUI

com actxserver

Hello,

I am trying to create a GUI that controls a third party program, which controls a camera.

I create the COM object as an activeX server as follows:

cameraHandle = actxserver('maxim.ccdcamera');

Now this object is in the workspace and I can interact with this object and make it do whatever I wish, no problem.

For example, the command for the camera to take a picture is:

invoke(cameraHandle,'Expose',exposureTime);

Now I would like to make one of the buttons in my GUI, do the same thing.

The code for the button is:

function buttonExpose_Callback(hObject, eventdata, handles)
% hObject     handle to buttonExpose
% handles     structure with handles and user data
% some commands here

How can I make this function act on the object cameraHandle?

Thanks!

Best Answer

Dmitry - if you wish to use the same code in your GUI, then instantiate the cameraHandle in the _OpeningFcn of the GUI, save it to the handles structure, and then reference it in your pushbutton code. Try the following

 function myGui_OpeningFcn(hObject, eventdata, handles, varargin)
 % Choose default command line output for untitled3
 handles.output = hObject;
 % create the COM object
 handles.cameraHandle = actxserver('maxim.ccdcamera');
 % Update handles structure
 guidata(hObject, handles);

And then in your push button callback, just do

 function buttonExpose_Callback(hObject, eventdata, handles)
 exposureTime = 42;
 invoke(handles.cameraHandle,'Expose',exposureTime);

Note that any callback that receives the handles structure as an input parameter, can reference the cameraHandles via

 handles.cameraHandle

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MATLAB: Error using handle.handle/set Invalid or deleted object.

In your callback for edit1 you replace the handle with the value extracted from the handle. That is confusing at the very least.

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Óscar - you have to be careful with the line of code

 set(handlesStacked(:),'ButtonDownFcn', {@axes2_ButtonDownFcn, handles});

The handles structure that is being passed as the third input parameter to axes2_ButtonDownFcn is a copy of the handles structure at the time that this set is called. So whenever the axes2 callback fires, the old copy of handles will be passed in...not the most recent version which is what you want.

You can try to do the following instead

 set(handlesStacked(:),'ButtonDownFcn', @axes2_ButtonDownFcn);

with the callback defined as

 function axes2_ButtonDownFcn(hObject, eventData)
     global position;
      % get the latest copy of *handles*

      handles = guidata(hObject);
      ...
      coordinates=get (gca, 'CurrentPoint'); 
      handles.coordinates=coordinates;
      ...
      % save this version of the handles structure

      guidata(hObject, handles);
 end

In the above code, we assume that hObject is a child of the parent figure (your GUI). See guidata for details.

-------

If the above assumption is not true, and so hObject is not a child of the parent figure (GUI), then using guidata to get and set the handles structure will fail. In that case, you can make a slight change to your original code and pass the parent figure handle as the third input to your callback.

Assuming that your set is called from the OpeningFcn of your GUI, then we can do

 function myGui_OpeningFcn(hObject, eventdata, handles, varargin)
 % do stuff
 ...
 set(handlesStacked(:),'ButtonDownFcn', {@axes2_ButtonDownFcn, hObject});
 % etc.

Now in your callback you change its signature and do

function axes2_ButtonDownFcn(hObject, eventData, hFigure)
   global position;
      % get the latest copy of *handles*
      handles = guidata(hFigure);
      ...
      coordinates=get (gca, 'CurrentPoint'); 
      handles.coordinates=coordinates;
      ...
      % save this version of the handles structure
      guidata(hFigure, handles);
 end

So when getting and setting the handles structure, we use the parent figure handle, hFigure.

You may want to try the second method as it is more similar to your original implementation.

Best Answer

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