Android - Services

A service is a component that runs in the background to perform long-running operations without needing to interact with the user and it works even if application is destroyed. A service can essentially take two states −

A service has life cycle callback methods that you can implement to monitor changes in the service's state and you can perform work at the appropriate stage. The following diagram on the left shows the life cycle when the service is created with startService() and the diagram on the right shows the life cycle when the service is created with bindService(): (image courtesy : android.com )

To create an service, you create a Java class that extends the Service base class or one of its existing subclasses. The Servicebase class defines various callback methods and the most important are given below. You don't need to implement all the callbacks methods. However, it's important that you understand each one and implement those that ensure your app behaves the way users expect.

actvity_main.xml

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

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="com.android.anil.services.MainActivity"
    tools:showIn="@layout/activity_main"
    android:orientation="vertical">
   
    <Button
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Start Service"
        android:id="@+id/button"
        android:layout_gravity="center_horizontal"
        android:layout_marginTop="50dp" />

    <Button
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="Stop Service"
        android:id="@+id/button2"
        android:layout_gravity="center_horizontal"
        android:layout_marginTop="50dp" />
</LinearLayout>

MainActvity.Java

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

package com.android.anil.services;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {
    Button startser,stopser;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        startser=(Button)findViewById(R.id.button);
        stopser=(Button)findViewById(R.id.button2);
        startser.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent=new Intent(getApplicationContext(),MyServices.class);
                startService(intent);
            }
        });
        stopser.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent=new Intent(getApplicationContext(),MyServices.class);
                stopService(intent);
            }
        });

    }
}

MyServices.Java

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

package com.android.anil.services;

import android.app.Service;
import android.content.Intent;
import android.os.IBinder;
import android.support.annotation.Nullable;
import android.widget.Toast;

/**
 * Created by Anil  on 11/23/15.
 */
public class MyServices extends Service {
    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }

    @Override
    public void onCreate() {
        Toast.makeText(MyServices.this, "Services is Created()", Toast.LENGTH_SHORT).show();
        super.onCreate();
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        Toast.makeText(MyServices.this, "Services is Running.........", Toast.LENGTH_SHORT).show();
        return super.onStartCommand(intent, flags, startId);
    }

    @Override
    public void onDestroy() {
        Toast.makeText(MyServices.this, "Services is Stopped", Toast.LENGTH_SHORT).show();
        super.onDestroy();
    }
}

AndroidManifest.xml
------------------------------

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.android.anil.services">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name"
            android:theme="@style/AppTheme.NoActionBar">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <service android:name=".MyServices"></service>
    </application>

</manifest>

Output is:

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

Android External Storage

Every Android-compatible device supports a shared "external storage" that you can use to save files. This can be a removable storage media (such as an SD card) or an internal (non-removable) storage. Files saved to the external storage are world-readable and can be modified by the user when they enable USB mass storage to transfer files on a computer

actvity_main.xml
----------------------

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:showIn="@layout/activity_main"
    tools:context=".MainActivity"
    android:orientation="vertical">

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/editText"
        android:hint="enter file name" />

    <EditText
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/editText2"
        android:layout_gravity="center_horizontal"
        android:hint="enter text" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Save"
        android:id="@+id/button"
        android:layout_gravity="center_horizontal" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Show"
        android:id="@+id/button2"
        android:layout_gravity="center_horizontal" />
</LinearLayout>

MainActvity.Java
-----------------------

package com.android.anil.externalstorage;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;

public class MainActivity extends AppCompatActivity {
    Button save,read;
    EditText filename,textname;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        save=(Button)findViewById(R.id.button);
        read=(Button)findViewById(R.id.button2);
        filename=(EditText)findViewById(R.id.editText);
        textname=(EditText)findViewById(R.id.editText2);
        save.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String filename1=filename.getText().toString();
                String data=textname.getText().toString();

                try {
                    File myFile = new File("/sdcard/"+filename1);
                    myFile.createNewFile();
                    FileOutputStream fOut = new

                            FileOutputStream(myFile);
                    OutputStreamWriter myOutWriter = new

                            OutputStreamWriter(fOut);
                    myOutWriter.append(data);
                    myOutWriter.close();
                    fOut.close();
                    Toast.makeText(MainActivity.this, filename1+"Saved", Toast.LENGTH_SHORT).show();



                } catch (FileNotFoundException e) {e.printStackTrace();}
                catch (IOException e) {e.printStackTrace();}


            }
        });
        read.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String s2=filename.getText().toString();
                StringBuffer stringBuffer = new StringBuffer();
                String aDataRow = "";
                String aBuffer = "";
                try {
                    File myFile = new File("/sdcard/"+s2);
                    FileInputStream fIn = new FileInputStream(myFile);
                    BufferedReader myReader = new BufferedReader(
                            new InputStreamReader(fIn));

                    while ((aDataRow = myReader.readLine()) != null) {
                        aBuffer += aDataRow + "\n";
                    }
                    myReader.close();

                } catch (IOException e) {
                    e.printStackTrace();
                }
                Toast.makeText(getApplicationContext

                        (),aBuffer,Toast.LENGTH_LONG).show();

            }
        });
    }
}

Output:
-----------------------