Application

public class UpdateApplication extends Application{    private static UpdateApplication instance = null;        public static Context mContext;        public synchronized static UpdateApplication getInstance() {        return instance;    }    @Override    public void onCreate() {        // TODO Auto-generated method stub        super.onCreate();        instance = this;    }}

得到系统级别的Context

Toast.makeText(UpdateApplication.getInstance().getApplicationContext(), "检测到新版本，后台正在默认更新", Toast.LENGTH_LONG);