Android tutorials made easy

For sharing simple data types between Activities or services we can make use or sharedPreferences , in android.

SharedPreferences or preferences are useful for simple dataTypes, where they are stored as Key/Values pairs in a xml file.

The below example will have two simple activities. One for input and the other for output display. We will shared data between the two activities using sharedPreferences.

NOTE: Used android 2.3.3 SDK

Project structure :

1. AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.app"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="10" />

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity android:name=".OutputActivity"
            android:label="Output screen"/>
    </application>

</manifest>

The manifest file has only two activities. One for taking user input and another for displaying the output.

2. main.xml (main layout)

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <TextView
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Enter the values" />

    <EditText
        android:id="@+id/valueOne"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10" >
        <requestFocus />
    </EditText>

    <EditText
        android:id="@+id/valueTwo"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10" />

    <EditText
        android:id="@+id/valueThree"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10" />

    <EditText
        android:id="@+id/valueFour"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10" />

    <Button
        android:id="@+id/buttonID"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/submit" />

</LinearLayout>

The main.xml layout has four input fields and a submit button. Each field will be stored using sharedPreferences and then later used in the OutputActivity.

3. output.xml (layout)

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:orientation="vertical" >



    <TextView

        android:id="@+id/textView1"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="Output Private"

        android:textAppearance="?android:attr/textAppearanceMedium" />



    <TextView

        android:id="@+id/privateTxt"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:textAppearance="?android:attr/textAppearanceMedium" />



    <TextView

        android:id="@+id/textView2"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="Output world read"

        android:textAppearance="?android:attr/textAppearanceMedium" />



    <TextView

        android:id="@+id/readTxt"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:textAppearance="?android:attr/textAppearanceMedium" />



    <TextView

        android:id="@+id/textView3"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="Output world write"

        android:textAppearance="?android:attr/textAppearanceMedium" />



    <TextView

        android:id="@+id/writeTxt"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:textAppearance="?android:attr/textAppearanceMedium" />



    <TextView

        android:id="@+id/textView4"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="Output world read/write"

        android:textAppearance="?android:attr/textAppearanceMedium" />



    <TextView

        android:id="@+id/readWriteTxt"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:textAppearance="?android:attr/textAppearanceMedium" />



</LinearLayout>

The output.xml layout has four textView fields. These four fields will display the four values shared by MainActivity using sharedPreferences.

4. MainActivity.java

package com.example.app;



import android.app.Activity;

import android.content.Context;

import android.content.Intent;

import android.content.SharedPreferences;

import android.content.SharedPreferences.Editor;

import android.os.Bundle;

import android.view.View;

import android.widget.Button;

import android.widget.EditText;





/**

 * 

 *  Activity class which demos the use of sharedPreferences for sharing data among different Activities 

 * 

 * @author Akshat

 *

 */

public class MainActivity extends Activity

{

 

 

 public static final String PREFS_PRIVATE = "PREFS_PRIVATE";

 public static final String PREFS_WORLD_READ = "PREFS_WORLD_READABLE";

 public static final String PREFS_WORLD_WRITE = "PREFS_WORLD_WRITABLE";

 public static final String PREFS_WORLD_READ_WRITE = "PREFS_WORLD_READABLE_WRITABLE";

 public static final String KEY_PRIVATE = "KEY_PRIVATE";

 public static final String KEY_WORLD_READ = "KEY_WORLD_READ";

 public static final String KEY_WORLD_WRITE = "KEY_WORLD_WRITE";

 public static final String KEY_WORLD_READ_WRITE = "KEY_WORLD_READ_WRITE";

 

 

 private SharedPreferences prefsPrivate;

 private SharedPreferences prefsWorldRead;

 private SharedPreferences prefsWorldWrite;

 private SharedPreferences prefsWorldReadWrite;

 

 

 

 

    /** Called when the activity is first created. */

    @Override

    public void onCreate(Bundle savedInstanceState)

    {

        super.onCreate(savedInstanceState);

       

        //Set the view for this activity to main.xml

        setContentView(R.layout.main);

       

        //Get hold of the submit button

        Button button = (Button) findViewById(R.id.buttonID);

      

        //Listener added to the submit button

        button.setOnClickListener(new Button.OnClickListener(){



   @Override

   public void onClick(final View v)

   {

    

    //Get the input values

    EditText valueOneTxt = (EditText) findViewById(R.id.valueOne);

    EditText valueTwoTxt = (EditText) findViewById(R.id.valueTwo);

    EditText valueThreeTxt = (EditText) findViewById(R.id.valueThree);

    EditText valueFourTxt = (EditText) findViewById(R.id.valueFour);

    

    

    // Create shared sharedPreferences

    // We created four different sharedPreferences with different modes

    prefsPrivate = getSharedPreferences(MainActivity.PREFS_PRIVATE, Context.MODE_PRIVATE);

    prefsWorldRead = getSharedPreferences(MainActivity.PREFS_WORLD_READ, Context.MODE_WORLD_READABLE);

    prefsWorldWrite = getSharedPreferences(MainActivity.PREFS_WORLD_WRITE, Context.MODE_WORLD_WRITEABLE);

    prefsWorldReadWrite = getSharedPreferences(MainActivity.PREFS_WORLD_READ_WRITE, Context.MODE_WORLD_READABLE+Context.MODE_WORLD_WRITEABLE);

    

    

    // To add values to the sharedPreferences, we get editors from the sharedPreferences

    Editor privateEdit = prefsPrivate.edit();

    Editor worldReadEdit = prefsWorldRead.edit();

    Editor worldWriteEdit = prefsWorldWrite.edit();

    Editor worldReadWriteEdit = prefsWorldReadWrite.edit();

    

    

    

    // With the Editor you can set String, boolean, float, int, and long types as key/value pairs

    // We save the four input values into the four different sharedPreferences

    privateEdit.putString(MainActivity.KEY_PRIVATE, valueOneTxt.getText().toString());

    worldReadEdit.putString(MainActivity.KEY_WORLD_READ, valueTwoTxt.getText().toString());

    worldWriteEdit.putString(MainActivity.KEY_WORLD_WRITE, valueThreeTxt.getText().toString());

    worldReadWriteEdit.putString(MainActivity.KEY_WORLD_READ_WRITE, valueFourTxt.getText().toString());

    

    //Commit the sharedPreferences into a file

    privateEdit.commit();

    worldReadEdit.commit();

    worldWriteEdit.commit();

    worldReadWriteEdit.commit();

    

    //Start another activity by passing an explicit intent

    Intent intent = new Intent(MainActivity.this, OutputActivity.class);    

    startActivity(intent);

   }

         

        });

      

    }

}

5. OutputActivity.java

package com.example.app;


import android.app.Activity;

import android.content.Context;

import android.content.SharedPreferences;

import android.os.Bundle;

import android.widget.TextView;



public class OutputActivity extends Activity

{

 

 private SharedPreferences prefsPrivate;

 private SharedPreferences prefsWorldRead;

 private SharedPreferences prefsWorldWrite;

 private SharedPreferences prefsWorldReadWrite;

 

 

 @Override

 protected void onCreate(Bundle savedInstanceState) 

 {

  super.onCreate(savedInstanceState);

  

  //Set the view for this activity to output.xml

  setContentView(R.layout.output);

  

  // Get hold of sharedPreferences

  prefsPrivate = getSharedPreferences(MainActivity.PREFS_PRIVATE, Context.MODE_PRIVATE);

  prefsWorldRead = getSharedPreferences(MainActivity.PREFS_WORLD_READ, Context.MODE_WORLD_READABLE);

  prefsWorldWrite = getSharedPreferences(MainActivity.PREFS_WORLD_WRITE, Context.MODE_WORLD_WRITEABLE);

  prefsWorldReadWrite = getSharedPreferences(MainActivity.PREFS_WORLD_READ_WRITE, Context.MODE_WORLD_READABLE+Context.MODE_WORLD_WRITEABLE);

  

  //Get hold of output textview - to display values

  TextView privateTxt = (TextView) findViewById(R.id.privateTxt);

  TextView readTxt = (TextView) findViewById(R.id.readTxt);

  TextView writeTxt = (TextView) findViewById(R.id.writeTxt);

  TextView readWriteTxt = (TextView) findViewById(R.id.readWriteTxt);

  

  

  // Set values form sharedPreferences to the textViews

  privateTxt.setText(prefsPrivate.getString(MainActivity.KEY_PRIVATE, "NA"));

  readTxt.setText(prefsWorldRead.getString(MainActivity.KEY_WORLD_READ, "NA"));

  writeTxt.setText(prefsWorldWrite.getString(MainActivity.KEY_WORLD_WRITE, "NA"));

  readWriteTxt.setText(prefsWorldReadWrite.getString(MainActivity.KEY_WORLD_READ_WRITE, "NA"));

  

  

 }

}

When the app is run, sharedPreferences xml files are created under /data/data/PACKAGE_NAME/

-----------------------------------------------------------------------------------------------------------

Screenshots:

MainActivity

OutputActivity

A simple android application which makes a HTTP POST request to a servlet.

The comments in the source are quite self explanatory. Leave a feedback for any clarifications.

SDK version used : 2.3.3

The project structure :

1. AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

    package="com.httpapp"

    android:versionCode="1"

    android:versionName="1.0" >



    <uses-sdk android:minSdkVersion="10" />

    <uses-permission android:name="android.permission.INTERNET"/>



    <application

        android:icon="@drawable/ic_launcher"

        android:label="@string/app_name" >

        <activity

            android:name=".HttpAppActivity"

            android:label="@string/app_name" >

            <intent-filter>

                <action android:name="android.intent.action.MAIN" />



                <category android:name="android.intent.category.LAUNCHER" />

            </intent-filter>

        </activity>

    </application>



</manifest>

We have to add the permission for internet access.

2. main.xml

This is your layout for your main activity

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="fill_parent"

    android:layout_height="fill_parent"

    android:orientation="vertical" >





    <TextView

        android:id="@+id/textView1"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="@string/firstname"

        android:textAppearance="?android:attr/textAppearanceLarge" />







    <EditText

        android:id="@+id/fnameID"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:ems="10" />





    <TextView

        android:id="@+id/textView4"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="@string/lastname"

        android:textAppearance="?android:attr/textAppearanceLarge" />





    <EditText

        android:id="@+id/lnameID"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:ems="10" >



        <requestFocus />

    </EditText>



    <Button

        android:id="@+id/submitID"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="@string/submit" />







    <TextView

        android:id="@+id/resultID"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:layout_weight="0.41" />



</LinearLayout>

3. strings.xml

<?xml version="1.0" encoding="utf-8"?>

<string name="hello">Hello World</string>

<string name="submit">submit</string>

<string name="firstname">First name</string>

</resources>

4. HttpAppActivity.java

package com.httpapp;

import android.app.Activity;

import android.os.Bundle;

import android.view.View;

import android.widget.Button;

import android.widget.EditText;

import android.widget.TextView;

public class HttpAppActivity extends Activity {

@Override

public void onCreate(Bundle savedInstanceState)

{

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

// Get the submit button and attach a listener to its click event

Button submitBtn = (Button)findViewById(R.id.submitID);

submitBtn.setOnClickListener(new Button.OnClickListener(){

public void onClick(View v)

{

EditText fnameText = (EditText)findViewById(R.id.fnameID); // Get a handle to the input box for first name

EditText lnameText = (EditText)findViewById(R.id.lnameID); // Get a handle to the input box for last name

//Make a call to our helper class

String result = ServletInterface.executeHttpRequest(fnameText.getText().toString(), lnameText.getText().toString());

TextView resultView = (TextView) findViewById(R.id.resultID); // Get the textView where we will display the result

resultView.setText(result); //set the returned result to the view

}

});

}

5. ServletInterface.java

package com.httpapp;

import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStream;

import java.io.InputStreamReader;

import java.io.OutputStream;

import java.io.UnsupportedEncodingException;

import java.net.URL;

import java.net.URLConnection;

import java.net.URLEncoder;

import android.util.Log;

/**

* This class is the interface for making calls to a Servlet in a remote server

public class ServletInterface

{

public static final String SERVER_URL = "http://10.0.2.2:8080"; // The server(Servlet) which will process the request. Note 10.0.2.2 is the localhost IP for emulator

public static final String CHAR_SET = "UTF-8"; // Encoding used for the parameters

public static String executeHttpRequest(String fname, String lname)

{

OutputStream output = null;

String response = "";

try

{

Log.i("HTTP :", "Preparing data");

// ------------------------------------------------------START: PREPARE CONNETION AND REQUEST ------------------------------- //

// Prepare the data string [ firstName=JOHN&lastName=SMITH ]

String data = URLEncoder.encode("firstName", CHAR_SET) + "=" + URLEncoder.encode(fname, CHAR_SET);

data += "&" + URLEncoder.encode("lastName", CHAR_SET) + "=" + URLEncoder.encode(lname, CHAR_SET);

URLConnection connection = new URL(SERVER_URL).openConnection(); // Create a connection to server using URL

connection.setDoOutput(true); // This means POST method to be used

connection.setRequestProperty("Accept-Charset", CHAR_SET); //For servers to know what encoding is used for the parameters

connection.setRequestProperty("Content-Type", "application/x-www-form-urlencoded;charset=" + CHAR_SET);

output = null;

output = connection.getOutputStream(); //open a Output stream from the connection for posting data

output.write(data.getBytes(CHAR_SET)); //Post data

//------------------------------------------------------ END: PREPARE CONNETION AND REQUEST --------------------------------- //

Log.i("HTTP :", "sending data");

InputStream responseStream = connection.getInputStream(); //This is when the request is actually fired

//------------------------------------------------------ START: READ RESPONSE ------------------------------------------------ //

Log.i("HTTP :", "Reading response");

BufferedReader rd = new BufferedReader(new InputStreamReader(responseStream,CHAR_SET)); // Connect a BufferReader to the inputStream

String line = null;

while ((line = rd.readLine()) != null) // Read the response line-by-line from the bufferedReader

{

response += line;

}

//------------------------------------------------------ END: READ RESPONSE ------------------------------------------------- //

}

catch (UnsupportedEncodingException e)

{

e.printStackTrace();

}

catch(IOException io)

{

//Log and check exp

}

finally

{

if (output != null) try { output.close(); } catch (IOException ignoreIO) {}

}

return response;

}

= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =

At the servlet end you can read the parameters using :

String fname = (String) request.getParameter("firstName");

String lname = (String) request.getParameter("lastName");

Android tutorials made easy

Passing data in Android using sharedPreferences

1. AndroidManifest.xml

2. main.xml (main layout)

3. output.xml (layout)

HTTP post from an android application using URLConnection

A simple android application which makes a HTTP POST request to a servlet.

The project structure :

1. AndroidManifest.xml

2. main.xml

3. strings.xml

4. HttpAppActivity.java

5. ServletInterface.java