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

    }

}