how to solve this problem with calendar alarm?

I am trying to make alarm ring when the time of calendar event is reached. I use to set AlertDialog when the alarm time 开发者_如何学运维is reached. But event when the application is closed, i need to notify the user through Alert Dialog. I have started the intent to the AlarmReceiver which extends BroadCastReceiver.My code is here in this link. AlarmReceiver.java: http://pastebin.com/0ch5hjp9 Alert.java: http://pastebin.com/bJAPAUV2 I am not getting alarm since i use to call alertdialog intent.

I am getting following exception when i reach the AlertDialog intent:

android.content.ActivityNotFoundException: Unable to find explicit activity class {com.android.todoapplication/android.todoapplication.Alert}; have you declared this activity in your AndroidManifest.xml?

make sure that you also set contentView to activity using setContentView() method. atleast an empty linearLayout.