从ComponentName对象获取上下文对象

Question

我需要获取当前运行的Activity并在Service中检测它。我是这样做的：

ActivityManager am = (ActivityManager) ServiceMessages.this.getSystemService(ACTIVITY_SERVICE);
List< ActivityManager.RunningTaskInfo >   taskInfo = am.getRunningTasks(1);
ComponentName componentInfo = taskInfo.get(0).topActivity;
componentInfo.getPackageName();
Log.d("topActivity", "CURRENT Activity ::" + componentInfo.getClassName());

并获取成功运行Activity的名称。但我需要将Toast消息传递给该Activity。所以，我需要将当前Activity的Context对象传递给Toast.makeText(context,text, length)。如果我有ComponentName，我该如何获取上下文对象？