Introduction

Most of the Android applications use an API to send and receive data from server to client. API is very useful when applications need to send or receive data.
In this tutorial, I will show you how to create a Restful JSON based API for Android application using ASP.NET and Microsoft SQL Server database.

Overview of the tutorial

This tutorial shows you the basic implementation of the RESTful API and will let you know how to create a Restful API in Visual Studio with ASP.NET using C#.
How to connect the android application with SQL Server Database
In this tutorial, I am using Visual Studio 2015 (you can use any version) and Android 1.5.1 version with minimum SDK API 18: Android 2.2 (Froyo).
First, we create an API
Step I
Download the required resources:
Download three JSON service DLL files from the link...
Step II
Open Visual Studio and create an ASP.NET Empty Web Application project.
For this
Go to File, then New. Click Project. From the new project window select web category. Then select ASP.NET Empty Web Application and give it a name. Select the project location from Browse. Make sure Create Directory for Solution is checked. Click Ok.
Now add DLL files in the .Net web application.
  1. Right-click on the project in Solution Explorer
  2. Form the menu, click on Add Reference to open the Reference Manager
  3. Click on Browse from left panel
  4. Then click browse button at bottom of Reference Manager
  5. Go to the location where save the download files
  6. Select three .dll files(which you have is download) and click on the add button
  7. Click ok
Now you need to add a handler class. For this,
  1. Go to the Project menu then click Add New Item.
  2. From Add New Item, select the web category from the left panel.
  3. From center select Generic Handler.
  4. Give it a name or left it default and click on the Add button.
Now create three new classes. To add class,
  1. Go to the Project menu and click on Add New Item.
  2. From the code category select class.
  3. Give the class name as SAPI.cs.
  4. Click the Add button.
In the same way, add two more classes named ISAPI and DBConnect.
Step III
SQL Server Database Creation
Open SQL Server Management Studio and connect with the server.
Create a database
  1. Right-click on the Database folder in Object Explorer and select a new database.
  2. Give the database a name (I have given serverdb) and click OK.
Now create tables. To create a table
  1. Click on the created database and click on New Query.
  2. SQLQuery window will open.
  3. Now execute the following SQL Query to create a table,
    SQL query to create a table
    1. CREATE TABLE UserData (
    2. Name VARCHAR(50),
    3. userName VARCHAR(50),
    4. password VARCHAR(50),
    5. PhoneNumber VARCHAR(50),
    6. CNIC VARCHAR(50),
Step IV
Make API and Connect Database with this and go back to the visual studio.
Now we programmatically save information in the database. To configure a connection open web.config file in Solution Explorer. Add the following line between <configuratio> and </configuration> tag
  1. <connectionStrings>
  2. <add name="ConString" connectionString="Data Source=DESKTOP-AU9BNOB;Initial Catalog=serverProjectdb;Integrated Security=True" providerName="System.Data.SqlCliesnt" />
  3. </connectionStrings>
In these lines change data source value to your Server Name. In the initial catalog change the database name with yours.
Now open DBConnect.cs class. Copy the following code into it and change the namespace with your project name.
  1. using System.Configuration;
  2. using System.Data.SqlClient;
  4. namespace TestProjectAPI
  5. {
  6. /// This class is used to connect to sql server database
  7. public class DBConnect
  8. {
  9. private static SqlConnection NewCon;
  10. private static stringconStr = ConfigurationManager.ConnectionStrings["ConString"].ConnectionString;
  11. public static SqlConnection getConnection()
  12. {
  13. NewCon = new SqlConnection(conStr);
  14. return NewCon;
  15. }
  16. public DBConnect()
  17. {
  19. }
  20. }
  21. }
    Step V
    Configuring the API
    To configure the API interface open Handler.ashx file and copy the following code into it. Use the correct namespace in your code.
    1. using JsonServices;
    2. using JsonServices.Web;
    4. namespace TestProjectAPI
    5. {
    6. public classHandler1: JsonHandler
    7. {
    8. public Handler1()
    9. {
    10. this.service.Name = " TestProjectAPI ";
    11. this.service.Description = "JSON API for android appliation";
    12. InterfaceConfiguration IConfig = new InterfaceConfiguration("RestAPI", typeof(ISAPI), typeof(SAPI));
    13. this.service.Interfaces.Add(IConfig);
    14. }
    15. }
    16. }
      Now we need to change ISAPI.cs class to an interface class. To do this open ISAPI.cs and the class keyword to interface. And extend the SAPI.cs class with this Interface ISAPI.cs.
      Here's the code to modify both classes.
      ISAPI.cs
      1. namespace TestProjectAPI
      2. {
      3. public interface ISAPI
      4. {
      6. }
      7. }
      SAPI.cs
      1. namespace TestProjectAPI
      2. {
      3. public interface SAPI: ISAPI
      4. {
      6. }
      7. }
      Now open ISAPI.cs and copy the following code. You can change methods according to your requirements.
      1. using System. Data;
      3. namespace TestProjectAPI
      4. {
      5. /// This interface declare the methods need to be implement.
      6. public interface ISAPI
      7. {
      8. void CreateNewAccount(string Name, string userName, string password, string PhoneNumber, string CNIC);
      9. }
      10. }
        Now open SAPI.cs and add the following code.
        1. using System;
        2. using System.Data;
        3. using System.Data.SqlClient;
        5. namespace TestProjectAPI
        6. {
        7. public classSAPI: ISAPI
        9. {
        10. SqlConnection dbConnection;
        11. public ServiceAPI()
        12. {
        13. dbConnection = DBConnect.getConnection();
        14. }
        15. public void CreateNewAccount(string Name, string userName, string password, string PhoneNumber, string CNIC) {
        16. if (dbConnection.State.ToString() == "Closed") {
        17. dbConnection.Open();
        18. }
        20. string query = "INSERT INTO UserDetails VALUES ('" + Name + "','" + userName + "','" + password + "','" + PhoneNumber + "','" + CNIC + "');";
        22. SqlCommand command = new SqlCommand(query, dbConnection);
        23. command.ExecuteNonQuery();
        25. dbConnection.Close();
        26. }
        27. }
          Now we have a successful code API.
          Step VI
          Now run the API in your browser. At first, the page gives you the error.
          error
          To solve this problem, simply add “/Handler1.ashx” to the end of the URL. In my case, the complete URL is “localhost:49702/Handler.ashx”. If you use another name of Handler class then add that name instead of Handler1.ashx.
          After adding this, if you see below type of screen it means your API is working.
          error
          Now at the end of URL add “?ANDROID” and complete URL becomes “localhost:49702/Handler.ashx?ANDROID”.
          Press enter and it will prompt you to save a zipped file.
          Now extract that zip file and start coding with Android Studio.
          Step 1
          Creating an Android project.
          Name the project Navigation
          Only one activity which is the Main Activity.
          Step 2
          Open the extracted file, then copy and paste the RestAPI.java file into your project. Change the package value with your package name.
          Step 3
          Add the following permission into AndroidMenifest.xml
          <uses-permissionandroid:name="android.permission.INTERNET"/>
          Step 4
          Open the activity_main.xml file and add the following code into it.
          1. <?xml version="1.0" encoding="utf-8"?>
          2. <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:paddingBottom="@dimen/activity_vertical_margin" android:paddingLeft="@dimen/activity_horizontal_margin" android:paddingRight="@dimen/activity_horizontal_margin" android:paddingTop="@dimen/activity_vertical_margin" tools:context="com.example.zubariaashraf.navigation.CreateUserActivity" android:background="@drawable/imag">
          4. <TextView android:id="@+id/textView1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/create_user_account" android:textAppearance="?android:attr/textAppearanceLarge" android:layout_alignParentTop="true" android:layout_centerHorizontal="true" />
          6. <EditText android:layout_width="wrap_content" android:layout_height="wrap_content" android:inputType="textPersonName" android:ems="10" android:id="@+id/name" android:layout_below="@+id/textView1" android:layout_alignParentRight="true" android:layout_alignParentEnd="true" />
          8. <EditText android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/uname" android:layout_below="@+id/name" android:layout_alignRight="@+id/name" android:layout_alignEnd="@+id/name" android:layout_alignLeft="@+id/name" android:layout_alignStart="@+id/name" />
          10. <EditText android:layout_width="wrap_content" android:layout_height="wrap_content" android:inputType="textPassword" android:ems="10" android:id="@+id/upassword" android:layout_below="@+id/uname" android:layout_alignRight="@+id/uname" android:layout_alignEnd="@+id/uname" />
          12. <EditText android:layout_width="wrap_content" android:layout_height="wrap_content" android:inputType="textPassword" android:ems="10" android:id="@+id/uRepassword" android:layout_below="@+id/upassword" android:layout_alignRight="@+id/upassword" android:layout_alignEnd="@+id/upassword" />
          14. <EditText android:layout_width="wrap_content" android:layout_height="wrap_content" android:inputType="phone" android:ems="10" android:id="@+id/phonenum" android:layout_below="@+id/uRepassword" android:layout_alignRight="@+id/uRepassword" android:layout_alignEnd="@+id/uRepassword" />
          16. <EditText android:layout_width="wrap_content" android:layout_height="wrap_content" android:inputType="number" android:ems="10" android:id="@+id/cnic" android:layout_below="@+id/phonenum" android:layout_alignParentRight="true" android:layout_alignParentEnd="true" />
          18. <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Name:" android:id="@+id/textView" android:layout_alignParentLeft="true" android:layout_above="@+id/uname" />
          20. <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="User Name:" android:id="@+id/textView5" android:layout_above="@+id/upassword" android:layout_alignParentLeft="true" android:layout_alignParentStart="true" />
          22. <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Password:" android:id="@+id/textView6" android:layout_alignBottom="@+id/upassword" android:layout_alignParentLeft="true" android:layout_alignParentStart="true" />
          24. <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Re-Password:" android:id="@+id/textView7" android:layout_above="@+id/phonenum" android:layout_alignParentLeft="true" android:layout_alignParentStart="true" />
          26. <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Phone #:" android:id="@+id/textView8" android:layout_alignBottom="@+id/phonenum" android:layout_alignParentLeft="true" android:layout_alignParentStart="true" />
          28. <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="CNIC:" android:id="@+id/textView9" android:layout_alignBottom="@+id/cnic" android:layout_alignParentLeft="true" android:layout_alignParentStart="true" />
          30. <Button android:id="@+id/btn_createuser" android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="@string/create_user_account" android:layout_alignParentBottom="true" android:layout_toRightOf="@+id/textView8" android:layout_toEndOf="@+id/textView8" android:layout_marginBottom="42dp" />
          32. <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:id="@+id/viewid" android:layout_above="@+id/btn_createuser" android:layout_alignRight="@+id/cnic" android:layout_alignEnd="@+id/cnic" />
          34. <!-- <TextView
          35. android:id="@+id/textView3"
          36. android:layout_width="wrap_content"
          37. android:layout_height="wrap_content"
          38. android:layout_alignLeft="@+id/textView2"
          39. android:layout_below="@+id/textView2"
          40. android:layout_marginTop="22dp"
          41. android:text="@string/lastname"
          42. android:textAppearance="?android:attr/textAppearanceMedium" />
          44. <TextView
          45. android:id="@+id/textView4"
          46. android:layout_width="wrap_content"
          47. android:layout_height="wrap_content"
          48. android:layout_alignRight="@+id/textView3"
          49. android:layout_below="@+id/textView3"
          50. android:layout_marginTop="20dp"
          51. android:text="@string/username"
          52. android:textAppearance="?android:attr/textAppearanceMedium" />
          54. <TextView
          55. android:id="@+id/textView5"
          56. android:layout_width="wrap_content"
          57. android:layout_height="wrap_content"
          58. android:layout_alignRight="@+id/textView4"
          59. android:layout_below="@+id/textView4"
          60. android:layout_marginTop="20dp"
          61. android:text="@string/password"
          62. android:textAppearance="?android:attr/textAppearanceMedium" />
          64. <TextView
          65. android:id="@+id/textView2"
          66. android:layout_width="wrap_content"
          67. android:layout_height="wrap_content"
          68. android:text="@string/firstname"
          69. android:textAppearance="?android:attr/textAppearanceMedium"
          70. android:layout_below="@+id/textView1"
          71. android:layout_alignParentLeft="true"
          72. android:layout_alignParentStart="true" />
          74. <EditText
          75. android:id="@+id/et_fisrtname"
          76. android:layout_width="wrap_content"
          77. android:layout_height="wrap_content"
          78. android:layout_alignBaseline="@+id/textView2"
          79. android:layout_alignBottom="@+id/textView2"
          80. android:layout_alignParentRight="true"
          81. android:ems="10"
          82. android:layout_toRightOf="@+id/textView6"
          83. android:layout_toEndOf="@+id/textView6">
          85. <requestFocus />
          86. </EditText>
          88. <EditText
          89. android:id="@+id/et_lastname"
          90. android:layout_width="wrap_content"
          91. android:layout_height="wrap_content"
          92. android:layout_alignBaseline="@+id/textView3"
          93. android:layout_alignBottom="@+id/textView3"
          94. android:layout_alignLeft="@+id/et_fisrtname"
          95. android:layout_alignRight="@+id/et_fisrtname"
          96. android:ems="10" />
          98. <EditText
          99. android:id="@+id/et_cu_username"
          100. android:layout_width="wrap_content"
          101. android:layout_height="wrap_content"
          102. android:layout_alignBaseline="@+id/textView4"
          103. android:layout_alignBottom="@+id/textView4"
          104. android:layout_alignLeft="@+id/et_lastname"
          105. android:layout_alignRight="@+id/et_lastname"
          106. android:ems="10" />
          108. <EditText
          109. android:id="@+id/et_cu_password"
          110. android:layout_width="wrap_content"
          111. android:layout_height="wrap_content"
          112. android:layout_alignBaseline="@+id/textView5"
          113. android:layout_alignBottom="@+id/textView5"
          114. android:layout_alignLeft="@+id/et_cu_username"
          115. android:layout_alignRight="@+id/et_cu_username"
          116. android:ems="10" />
          118. <Button
          119. android:id="@+id/btn_createuser"
          120. android:layout_width="wrap_content"
          121. android:layout_height="wrap_content"
          122. android:text="@string/create_user_account"
          123. android:layout_alignParentBottom="true"
          124. android:layout_centerHorizontal="true" />
          126. <EditText
          127. android:layout_width="wrap_content"
          128. android:layout_height="wrap_content"
          129. android:inputType="textPassword"
          130. android:ems="10"
          131. android:id="@+id/editText"
          132. android:layout_below="@+id/et_cu_password"
          133. android:layout_alignParentRight="true"
          134. android:layout_alignParentEnd="true"
          135. android:layout_alignLeft="@+id/et_cu_password"
          136. android:layout_alignStart="@+id/et_cu_password" />
          138. <TextView
          139. android:layout_width="wrap_content"
          140. android:layout_height="wrap_content"
          141. android:text="Re-password:"
          142. android:id="@+id/textView"
          143. android:layout_alignBottom="@+id/editText"
          144. android:layout_alignLeft="@+id/textView5"
          145. android:layout_alignStart="@+id/textView5" />
          147. <EditText
          148. android:layout_width="wrap_content"
          149. android:layout_height="wrap_content"
          150. android:inputType="phone"
          151. android:ems="10"
          152. android:id="@+id/editText2"
          153. android:layout_below="@+id/editText"
          154. android:layout_alignParentRight="true"
          155. android:layout_alignParentEnd="true"
          156. android:layout_alignLeft="@+id/editText"
          157. android:layout_alignStart="@+id/editText" />
          159. <TextView
          160. android:layout_width="wrap_content"
          161. android:layout_height="wrap_content"
          162. android:textAppearance="?android:attr/textAppearanceMedium"
          163. android:text="Phone #:"
          164. android:id="@+id/textView6"
          165. android:layout_alignBottom="@+id/editText2"
          166. android:layout_alignLeft="@+id/textView"
          167. android:layout_alignStart="@+id/textView" />
          169. <TextView
          170. android:layout_width="wrap_content"
          171. android:layout_height="wrap_content"
          172. android:textAppearance="?android:attr/textAppearanceMedium"
          173. android:text="CNIC:"
          174. android:id="@+id/textView7"
          175. android:layout_below="@+id/editText2"
          176. android:layout_alignLeft="@+id/textView4"
          177. android:layout_alignStart="@+id/textView4"
          178. android:layout_alignParentStart="false" />-->
          179. </RelativeLayout>
            Step 5
            Add two more classes named
            UserDetailsTable.java and JSONParser.java.
            UserDetailsTable.java class-map database objects to java objects.
            JSONParser.java class used to parse JSONObjects
            Step 6
            Now open UserDetailsTable.java and add the following code into it.
            1. package com.example.zubariaashraf.navigation;
            3. import android.content.Intent;
            5. /**
            6. * Created by Zubaria Ashraf on 8/2/2016.
            7. */
            8. public class UserDetailsTable
            9. {
            10. String Name, userName, password, PhoneNumber, CNIC;
            11. int id;
            13. public UserDetailsTable(String Name, String userName,
            14. String password, String PhoneNumber, String CNIC)
            15. {
            16. super();
            17. this.id = id;
            18. this.Name = Name;
            19. this.userName = userName;
            20. this.password = password;
            21. this.PhoneNumber = PhoneNumber;
            22. this.CNIC = CNIC;
            23. }
            25. public UserDetailsTable()
            26. {
            27. super();
            28. this.id = 0;
            29. this.Name = null;
            30. this.userName = null;
            31. this.password = null;
            32. this.PhoneNumber = null;
            33. this.CNIC = null;
            36. }
            38. public int getId()
            39. {
            40. return id;
            41. }
            42. public void setId(int id)
            43. {
            44. this.id = id;
            45. }
            47. public String getName()
            48. {
            49. return Name;
            50. }
            52. public void setName(String Name)
            53. {
            54. this.Name = Name;
            55. }
            57. public String getUserName()
            58. {
            59. return userName;
            60. }
            62. public void setUserName(String userName)
            63. {
            64. this.userName = userName;
            65. }
            67. public String getPassword()
            68. {
            69. return password;
            70. }
            72. public void setPassword(String password)
            73. {
            74. this.password = password;
            75. }
            77. public String getPhoneNumber()
            78. {
            79. return PhoneNumber;
            80. }
            82. public void setPhoneNumber(String PhoneNumber)
            83. {
            84. this.PhoneNumber = PhoneNumber;
            85. }
            87. public String getCNIC()
            88. {
            89. return CNIC;
            90. }
            92. public void setCNIC(String CNIC)
            93. {
            94. this.CNIC = CNIC;
            95. }
            97. }
              Now open JSONParser.java and add the following code into it. You can modify this class according to your requirements.
              1. package com.example.zubariaashraf.navigation;
              3. import org.json.JSONArray;
              4. import org.json.JSONException;
              5. import org.json.JSONObject;
              7. import android.annotation.SuppressLint;
              8. import android.util.Log;
              10. /**
              11. * Created by Zubaria Ashraf on 8/2/2016.
              12. */
              13. public class JSONParser
              14. {
              16. public JSONParser()
              17. {
              18. super();
              19. }
              20. }
                Now open Main Activity.java and add the following code into it.
                1. package com.example.zubariaashraf.navigation;
                3. import android.content.Context;
                4. import android.os.AsyncTask;
                5. import android.os.Bundle;
                6. import android.app.Activity;
                7. import android.util.Log;
                8. import android.view.Menu;
                9. import android.view.MenuItem;
                10. import android.view.View;
                11. import android.widget.Button;
                12. import android.widget.EditText;
                13. import android.support.v4.app.NavUtils;
                14. import android.annotation.TargetApi;
                15. import android.content.Intent;
                16. import android.os.Build;
                17. import android.widget.TextView;
                18. import android.widget.Toast;
                20. import org.json.JSONObject;
                22. import java.sql.SQLException;
                24. public class CreateUserActivity extends Activity
                25. {
                27. EditText etName, etUsername, etPassword, rPassword, pNumber, uCnic;
                28. Button btnCreateUser;
                29. Context context;
                30. boolean value;
                31. String username;
                33. @Override
                34. protected void onCreate(Bundle savedInstanceState)
                35. {
                36. super.onCreate(savedInstanceState);
                37. setContentView(R.layout.activity_create_user);
                38. context = this;
                39. Show the Up button in the action bar.
                40. setupActionBar();
                42. etName = (EditText) findViewById(R.id.name);
                43. etUsername = (EditText) findViewById(R.id.uname);
                44. etPassword = (EditText) findViewById(R.id.upassword);
                45. rPassword = (EditText) findViewById(R.id.uRepassword);
                46. pNumber = (EditText) findViewById(R.id.phonenum);
                47. uCnic = (EditText) findViewById(R.id.cnic);
                49. btnCreateUser = (Button) findViewById(R.id.btn_createuser);
                51. btnCreateUser.setOnClickListener(
                52. new View.OnClickListener()
                53. {
                55. @Override
                56. public void onClick(View v)
                57. {
                58. // TODO Auto-generated method stub
                59. String firstname, password, rePassword, Pnumber, ucnic;
                60. firstname = etName.getText().toString();
                61. username = etUsername.getText().toString();
                62. password = etPassword.getText().toString();
                63. rePassword = rPassword.getText().toString();
                64. Pnumber = pNumber.getText().toString();
                65. ucnic = uCnic.getText().toString();
                67. UserDetailsTable userDetail = new UserDetailsTable(firstname, username, password, Pnumber, ucnic);
                68. new AsyncCreateUser().execute(userDetail);
                70. }
                71. });
                72. }
                74. ////create user account
                76. protected class AsyncCreateUser extends
                77. AsyncTask < UserDetailsTable, Void, Void >
                78. {
                80. @Override
                81. protected Void doInBackground(UserDetailsTable...params)
                82. {
                84. RestAPI api = new RestAPI();
                85. try
                86. {
                88. api.CreateNewAccount(params[0].getName(),
                89. params[0].getUserName(),
                90. params[0].getPassword(),
                91. params[0].getPhoneNumber(),
                92. params[0].getCNIC());
                94. } catch (Exception e)
                95. {
                96. // TODO Auto-generated catch block
                97. Log.d("AsyncCreateUser", e.getMessage());
                99. }
                100. return null;
                101. }
                103. @Override
                104. protected void onPostExecute(Void result)
                105. {
                106. store(username);
                107. Intent i = new Intent(CreateUserActivity.this, LoginActivity.class);
                108. startActivity(i);
                109. }
                111. }
                113. @Override
                114. public boolean onOptionsItemSelected(MenuItem item)
                115. {
                116. switch (item.getItemId())
                117. {
                118. case android.R.id.home:
                120. NavUtils.navigateUpFromSameTask(this);
                121. return true;
                122. }
                123. return super.onOptionsItemSelected(item);
                124. }
                126. }
                  Step 7
                  Now run the application
                  To run this, the application should know the correct URL of the API. So to add this open the RestAPI class and here you will see an attribute called urlString with "http://DESKTOP-AU9BNOB/Handler1.ashx" URL as in my RestAPI.
                  So to run this application on the emulator you need to host your API on a local server. But if you want to run an application on a real android device then you have to host API in the public hosting site.
                  Run the application and enjoy it.
                  After hosting API on local or public hosting server change the URL from the RestAPI.
                  Read more articles on Android: