title: How to prevent duplicate entry in registration activity
body: <p>I would like it that when a user registers a username in my app if that username is already taken that he/she will get a toast saying "Username is already taken".</p>
  
  <p>I already included the UNIQUE constraint in my Database and it works fine but in the activity itself I would like to let the user know that the Username they are trying to register already exist.</p>
  
  <pre><code>    package com.fullfrontalgames.numberfighter;
  
  import android.app.Activity;
  import android.content.Intent;
  import android.os.Bundle;
  import android.view.View;
  import android.widget.Button;
  import android.widget.EditText;
  import android.widget.Toast;
  
  public class Register extends Activity {
      EditText UsernameReg, PasswordReg, PasswordConfirm, EmailReg;
  
      Button Register;
  
      DBAdapter db;
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          // TODO Auto-generated method stub
          super.onCreate(savedInstanceState);
          setContentView(R.layout.register);
  
          // get Instance of Database Adapter
          final DBAdapter db = new DBAdapter(this);
          db.open();
  
          // Get reference of views.
          UsernameReg = (EditText)findViewById(R.id.UsernameReg);
          PasswordReg = (EditText)findViewById(R.id.PasswordReg);
          EmailReg = (EditText)findViewById(R.id.EmailReg);
          PasswordConfirm = (EditText)findViewById(R.id.PasswordConfirm);
  
          Register = (Button)findViewById(R.id.Register);
          Register.setOnClickListener(new View.OnClickListener() {
  
              @Override
              public void onClick(View v) {
                  // TODO Auto-generated method stub
                  String Username = UsernameReg.getText().toString();
                  String Password = PasswordReg.getText().toString();
                  String PassConfirm = PasswordConfirm.getText().toString();
                  String Email = EmailReg.getText().toString();
                  String TakenUsername = db.getData();
  
                  // Check if any of the field are vacant.
                  if (Username.equals("") || Password.equals("") || PassConfirm.equals("")) {
                      Toast.makeText(getApplicationContext(), "Field Vacant", Toast.LENGTH_LONG)
                              .show();
                      return;
                  }
                  // Check if both passwords matches
                  if (!Password.equals(PassConfirm)) {
                      Toast.makeText(getApplicationContext(), "Password does not match",
                              Toast.LENGTH_LONG).show();
                      return;
                  }
                  if (Username.equals(TakenUsername))
  
                  {
                      Toast.makeText(getApplicationContext(), "Username Already Taken",
                              Toast.LENGTH_LONG).show();
                      return;
                  } else {
                      // Save data in database
                      db.insertPlayer(Username, Password, Email);
                      Toast.makeText(getApplicationContext(), "Account Successfully Created ",
                              Toast.LENGTH_LONG).show();
                      startActivity(new Intent("com.fullfrontalgames.numberfighter.Login"));
                  }
              }
  
          });
  
      }
  
  }
  </code></pre>