Android How to - Perform Long-Running Tasks in a Service

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The following code shows how to Perform Long-Running Tasks in a Service. You will simulate the service of downloading a file from the Internet.

Example

Populate the MyService.java file with the following code:

package com.java2s.myapplication3.app;
//from w ww . ja  v a2s  .  com
import java.net.MalformedURLException;
import java.net.URL;

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

public class MyService extends Service {

    @Override
    public IBinder onBind(Intent arg0) {
        return null;
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        try {
            int result = DownloadFile(new URL("http://www.your server.com/somefile.pdf"));
            Toast.makeText (getBaseContext(),
                    "Downloaded " + result + " bytes",
                    Toast.LENGTH_LONG).show();
        } catch (MalformedURLException e) {
            e.printStackTrace();
        }
        return START_STICKY;
    }

    private int DownloadFile(URL url) {
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return 100;
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        Toast.makeText (this, "Service Destroyed", Toast.LENGTH_LONG).show();
    }
}

In the AndroidManifest.xml file, add the following statement:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.java2s.Services"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk android:minSdkVersion="14" />

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

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

</manifest>

Main layout xml file

<?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" >

<Button android:id="@+id/btnStartService"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="Start Service"
    android:onClick="startService"/>

<Button android:id="@+id/btnStopService"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:text="Stop Service"
    android:onClick="stopService" />

</LinearLayout>

Main Activity Java code

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
/*from  w ww.j  a va  2 s . co  m*/
public class MainActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }

    public void startService(View view) {
           startService(new Intent(getBaseContext(), MyService.class));
    }

    public void stopService(View view) {
       stopService(new Intent(getBaseContext(),MyService.class));
    }
}

Note

Clicking the Start Service button will start the service. To stop the service, click the Stop Service button.

The activity is frozen for a few seconds before the Toast class displays the "Downloaded 100 bytes" message.

Note 2

The service runs on the same thread as your activity. In this case, because the service is suspended for five seconds, so is the activity.

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