Android : Need some advice regarding my system:

I am making a system (Android) for my software engineering class and this is a brief description of the system: It is an app for a gym that shows the list of the workouts that can be done. This is the step-by-step processes that I made for the system:

1. 
   

   Admin log in (in order to access the app- only the admin can open the app because the app serves as a kioks) THIS PART IS DONE

   
   


2. 
   

   Current Users page (this is a page that shows who are currently using the app in the gym) this part is not done yet but I am doing this part by database: DESCRIPTION: a. users are required to register to the app (done by database: involves username and password columns) b. if the user is registered and ready to add into current users they will login their username and password

   
   


3. 
   

   User Workout page (after logging in from current users page this page will show) this part is not done yet DESCRIPTION: a. This page shows the user's history workout (I need a suggestion on how will I record the workout history, is it from database?) b. If the user wants a NEW WORKOUT it will display a ListView of workouts (please read this, this is where I have a hard time) i. Each Workout has: (name, muscletype, rating, machineOrNot, videopath) ii. I am having a hard time putting many workouts in a database, I tried parsing it from XML file and somewhat I know the entries get inserted successfully but i cant make it into the listview for nullpointerexception error

   
   

I really need some advices in order to successfully program the system. Also, each workouts has a video in what way I can link it to each workouts?

Thank you all!