Mouse Listener in ROI Manager

Hello,
I have created a GUI via a plugin inside Imagej which also contains ROI manager as a button. When pressed, it opens up ROI manager.
Inside my plugin, there will be a lot of versatile wand tool selections added, later to be combined.
ROI Manager as default, does not delete other added versatile wand tool selections after a combination. It creates one data which includes all versatile wand tool selections, but keeps each individual selection also.
So inside my plugin, I need to delete all other data after pressing ‘combine’ button inside ROI, so that only combined data remains inside ROI.
My question is, how can I know when ‘combine’ button of ROI is clicked ? I can do it for buttons I have created inside my plugin, but this button belongs to ROI manager.

Just a suggestion instead of overwriting a listener. Below is a java plugin example to
to combine three ROIManager ROI’s, creates a new combined ROI and deletes the old ROI’s.

So my suggestion would be to call that actions in your GUI.

import ij.IJ;
import ij.ImagePlus;
import ij.plugin.PlugIn;
import ij.plugin.frame.RoiManager;

public class My_Plugin implements PlugIn {

	public void run(String arg) {
		ImagePlus imp = IJ.openImage("http://wsr.imagej.net/images/blobs.gif");
		imp.show();
		//ImagePlus imp = IJ.getImage();
		RoiManager rm = RoiManager.getInstance();
		if (rm==null) rm = new RoiManager();
		imp.setRoi(40,30,64,49);
		rm.addRoi(imp.getRoi());
		imp.setRoi(149,70,72,55);
		imp.setRoi(149,70,72,55);
		rm.addRoi(imp.getRoi());
		imp.setRoi(100,105,79,58);
		imp.setRoi(100,105,79,58);
		rm.addRoi(imp.getRoi());
		rm.select(0);
		rm.setSelectedIndexes(new int[]{0,1,2});
		rm.runCommand(imp,"Combine");
		rm.addRoi(imp.getRoi());
		rm.setSelectedIndexes(new int[]{0,1,2});
		rm.runCommand(imp,"Delete");
		rm.select(0);
		
	}

}