动态改变actionbutton。

modifyActionButton.java

	/* Called whenever we call invalidateOptionsMenu() */
	@Override
	public boolean onPrepareOptionsMenu(Menu menu) {
		Logger.d("======== onPrepareOptionsMenu =========="+mSubscribed);
		MenuItem item = menu.findItem(R.id.action_subscribe);
		if (mSubscribed) {
			item.setTitle(R.string.menu_unsubscribe);
			item.setIcon(R.drawable.btn_actionbar_unsubscriptions);
		} else {
			item.setTitle(R.string.menu_subscribe);
			item.setIcon(R.drawable.btn_actionbar_subscriptions);
		}

		return super.onPrepareOptionsMenu(menu);
	}
	
	supportInvalidateOptionsMenu();