How to control through opc data access explorer

I can not use opc data as a button to capture image, my code is:

da = opcda('localhost', 'KEPware.KEPServerEx.V4');
connect(da);
grp = addgroup(da);
itm1 = additem(grp, 'Channel1.Device1.Group1.capture');
data = read(itm1,'device');
opcdata= data.Value;
if (opcdata==1)
    opcdata=0;
vid=handles.vid;
pause(3);
data=getsnapshot(vid);
imshow(data);
savename = strcat('Desktop' ,'hinh', '.jpg'); 
imwrite(data,savename);

[Image Analyst]

http://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup

[Samuel Vergara]

You got some error that can share? The only thing that I do is use the connect after the item adition, but I'm not sure if it's the solution.

da = opcda('localhost', 'KEPware.KEPServerEx.V4');
grp = addgroup(da);
itm1 = additem(grp, 'Channel1.Device1.Group1.capture');
connect(da);