• Understanding how activities are rendered in the application. Also, what do we mean by activities in Android?
• Understanding the concept of Activity Life Cycle.
• Learning about Intents in Android, which will be your best friend in Android application development. It will help you communicate within you activities.

• Add all necessary dependencies for your project in the build.gradle file. Gradle is a build system commonly used in all java applications to automate building, testing and deployment. build.gradle contains scripts to automate several tasks like simply copying some file from one directory to other. It contains compiledSdkVersion, buildTypes and dependencies. The following Dependencies need to be added:
  • appcompat - maven dependency for using various frameworks
  • recyclerview - dependency for using the recycler view in our app
  • cardview - for using cardview class with the viewholder class
  • constraint-layout - for designing in constraint layout

dependencies {
    implementation 'com.android.support:appcompat-v7:28.0.0'
    implementation 'com.android.support:recyclerview-v7:28.0.0'
    implementation 'com.android.support:cardview-v7:28.0.0'
    implementation 'com.android.support.constraint:constraint-layout:2.0.4'
    implementation 'com.android.support:design:28.0.0-rc01'
    implementation 'de.hdodenhof:circleimageview:3.0.0'
}

• Now after setting the proper dependencies, we can see main activity being present by default in our application. This main activity class will be the first function to be executed when our application will be launched. We can create new activities for different pages of your app under com.example.[appname] by creating new classes under this directory.

• Each activity can be designed using xml and the component .xml files can be found in the layout folder of the res directory. In the activity.xml file we can design our activity screen using XML and drag & drop methods.
• Always remember to map the elements in the .xml file to your class activity files.
• The drawable folder under res (resource) directory will contain all your images, designs etc. files needed for the frontend.
• Now go on creating as many activities you will be using in your app. Always make sure that the main activity will regulate the flow of the application i.e., which activity will be followed next. Intents will be come handy here.

• Creating placeholders for the name, username, mobile number, password for the user input in the Registration activity. The Login activity will require only username and password. Intents can be used here to take the values of these placeholders and transfer it across our list of activity classes.
• Create a UserData class which will contain the way in which data will be stored in our database. Idea is to have objects of users in which each object shall contain username and mobile number.
• Once we are done with this, we have to connect our database to our application where user data will be stored. Create a DatabaseHelper class which will be used to connect SQLite3. SQLiteOpenHelper is used to create an object to create tables, open or manage the database. Here also define the schema of the database by executing a create table query in the onCreate() method in DatabaseHelper class.
  • Now we need the Registration activity class to call our DatabaseHelper class using an object of SQLiteHelper to send the data inserted in the placeholders to DatabaseHelper class where these will be fed to the database. This method shall contain the username, mobile number, password as the arguments.
  • Create an insert method in DatabaseHelper class which will receive the arguments from Registration activity and feed it to the database using ContentValues. You can have the return type of this insert method as Boolean to check whether the data has been successfully inserted or not. ContentValues is a map like class that matches string key and inserts the data given into it as arguments into the table
• Now in the Login activity class we have fields for username and password. We need to check that if this user is present in our database or not and then if there is a user present we need to authenticate that the user has entered correct password or not.
  • Create a check_username method in DatabaseHelper class which receives the username as argument to check if it is present in the database or not.
  • Create a match method in our DatabaseHelper class which receives username and password as arguments and checks if the password matches with the password present in the database.
  • Here in the match method we have to use cursor for iterating through the table stored in the database. Cursor basically contains the result of a query made against a database in android. Use the getCount() method of Cursor which returns the number of matches, if it returns zero hence no matches found and user is not present in the database.
• Also check out these commands for creating and updating the tables of your database.
  • Executing create table - onCreate() This will contain the database query executing command for creating a table.
  • Updating table - onUpgrade() This will contain the command for updating data in our database.

• We have to create a custom recycler view class. RecyclerView is a class under ViewGroup which helps in building and displaying large sets of data efficiently. In our case, we will use it to build a list of items which shall display the username, phone number and a delete button for each element in the list. ViewHolder class provides all the functionality for each list items. To implement a custom RecyclerView we would need a Custom Adapter also. Adapter associates the data with the ViewHolder class.
• Before moving ahead we need to create a method getAllContacts() in the DatabaseHelper class which returns all the data present in the database by iterating through it using Cursor. This is first needed to get the data in an ArrayList. Then we move onto creating our recycler view.
• Now create a ContactsView class which is basically the RecyclerView wrapper class. This class calls on the RecyclerViewAdapter class with arguments as the ArrayList of UserData. This also defines the layout of the list i.e. whether you want a vertical list or a horizontal list. It contains two methods -
  • onCreate()- calls the RecyclerViewAdapter class and sends the ArrayList of UserData as argument. It also manages the layout of the list view. This method will call the next method loadContactList().
  • loadContactList() - This method should have an instance of the database which is used to call using the DatabaseHelper object to get the list of data stored in the database. It also calls the getAllContacts()to populate the adapter list in the next step.
• Create a custom RecyclerViewAdapter class which will denote each row of the database. In this class we should have an ArrayList of UserData to receive the same from ContactsView. Each of the views in the list will contain username, phone number and a delete button. Each of the list view item is represented by RecyclerViewAdapter.
• This class has various methods like
  • onCreateViewHolder() - used to populate the list receiving data from UserData.
  • getItemCount() - returns the number of rows in the list.
  • ViewHolder() - contains a database instance and deleting method. The delete button is used with a onClickListener event to delete the current list item when this button is clicked.
  • Create a deleteContact() method in the DatabaseHelper class that receives aUserData to be deleted and deletes that data from the database.

• Create a ContactDetails activity class along with call button, mobile number and profile photo.
• Add the permission for using the camera and calling option in the details activity. The camera and call permissions have to be allowed manually from the settings of the android device.
• Create two different onClickListener methods, one for camera access and clicking the image, while the other is for making a calling method which is implemented by using Intent methods for performing the call function.

  public static final int CAMERA_REQUEST=9999;
  
  // mention these in the onclick listener functions
  Intent callintent = new Intent(Intent.ACTION_CALL); // for call
  Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE); // for camera 
  
  

• Now you also have to store this in the profile image, for which we have to convert our image into bitmap and then store. Before inserting into database, you need to convert your Bitmap image into byte array first then apply it using database query.
• This bitmap image has to be stored in the database using an instance of it. It should call a method InsertImage() in DatabaseHelper class which takes in the bitmap image and converts it into a byte array. The InsertImage() method inserts the image into the database using the two arguments byte array and username. Query commands are executed here. It uses the Cursor again to search for the corresponding username and then with the help of ContentValues inserts into the database.