eclipse default handler IHandler interface “the chosen operation is not enabled”

NOTE: These two methods:

Tip: Subclass AbstractHandler rather than implementing IHandler. but you can use it to the below section you need to set:

IHandler the chosen operation is not enabled

NOT USE popupMenus instead of Menus

isEnabled: should be set to true

isHandled:should be set to true

import org.eclipse.core.commands.AbstractHandler;
import org.eclipse.core.commands.ExecutionEvent;
import org.eclipse.core.commands.ExecutionException;
import org.eclipse.core.commands.IHandler;
import org.eclipse.core.commands.IHandlerListener;
import org.eclipse.jface.dialogs.MessageDialog;
import org.eclipse.swt.widgets.MessageBox;
import org.eclipse.ui.IWorkbenchWindow;
import org.eclipse.ui.handlers.HandlerUtil;

public class MyHandler implements IHandler {

    private FontChanger font=FontChanger.getInstance();
    @Override
    public Object execute(ExecutionEvent event) throws ExecutionException {
        // TODO Auto-generated method stub

        IWorkbenchWindow window = HandlerUtil.getActiveWorkbenchWindowChecked(event);
        MessageDialog.openInformation(
                window.getShell(),
                "Demo",
                "Hello, Eclipse world");
        font.decreaseSize();
        return null;
    }
    @Override
    public void addHandlerListener(IHandlerListener handlerListener) {
        // TODO Auto-generated method stub

    }
    @Override
    public void dispose() {
        // TODO Auto-generated method stub

    }
    @Override
    public boolean isEnabled() {
        // TODO Auto-generated method stub
        return true;
    }
    @Override
    public boolean isHandled() {
        // TODO Auto-generated method stub
        return true;
    }
    @Override
    public void removeHandlerListener(IHandlerListener handlerListener) {
        // TODO Auto-generated method stub

    }

}

menu :

http://stackoverflow.com/questions/1342532/how-to-add-items-in-popup-menu

add it as a menu or menu item

Eclipse base location uri for menus

Since they are impossible to find on the net here is the list of all base location uri's in eclipse that are used in the org.eclipse.ui.menus extension point:
menu:org.eclipse.ui.main.menu // the top-level menu
popup:org.eclipse.ui.popup.any // all pop-up menus
toolbar:org.eclipse.ui.main.toolbar // the top-level tool bar
toolbar:org.eclipse.ui.trim.command1 // the top left trim (main toolbar area)
toolbar:org.eclipse.ui.trim.command2 // the top right trim (perspective switcher area)
toolbar:org.eclipse.ui.trim.vertical1 // the left vertical trim
toolbar:org.eclipse.ui.trim.vertical2 // the right vertical trim
toolbar:org.eclipse.ui.trim.status // the status line trim
to access the menu/toolbar/popup of a part (view or editor):
menu:partid //the part's chevron menu
toolbar:partid //the part's toolbar (cannot contain other toolbars)
popup:partid //the part's popup menu (register the context menu in createPartControl first)

eclipse plugin menu gray out

check the handler class is correct set ,or not implement