We will now see a small example on how to perform authentication using Android. The example we are going to see here uses the login and password combination technique. We are going to start with a very simple example and increase the functionalities as well as the complexities in every iteration.

First of all, we will define EditText and Button, shown as follows:

<EditText
   android:id="@+id/etUsername"
   android:layout_width="wrap_content"
   android:layout_height="wrap_content"/>
<EditText
   android:id="@+id/etPassword"
   android:layout_width="wrap_content"
   android:layout_height="wrap_content"
   android:inputType="textPassword"/> 
<Button
   android:id="@+id/bLogin"
   android:layout_width="wrap_content"
   android:layout_height="wrap_content"
   android:onClick="login"
   android:text="Login"/>

Now, we are going to check whether the combination of a username and password is good or not. To start, we will simply check whether both the username...