IntentService

[embedyt]https://www.youtube.com/watch?v=Oenqq3ZCo9Q[/embedyt]

In this video, we will learn how to start and use IntentServices in Android.
An IntentService runs in the background independently from an activity and handles all the incoming work on a HandlerThread, so we don’t have to take care of creating our own background thread in order to not block the UI thread.
Since IntentService is a subclass of Service and therefore affected by the Android Oreo background execution limits, the recommended approach is to use the JobIntentService instead, which uses JobScheduler to enqueue a job on API 26 and higher.
In this video we will use a different approach and run our IntentService as a foreground service on Android Oreo and higher, but as a normal background service on API 25 and lower.
For this, we create a class that extends IntentService, where we provide a default constructor and override onCreate, onHandleIntent and onDestroy. We don’t have to implement onBind, since the superclass provides a default implementation that returns null. When the Service is created, onCreate is triggered. Here, we display a persistent notification (after creating a notification channel in the Application class) and call startForeground if the SDK_INT is VERSION_CODES.O or higher to promote the service to a foreground service. In onHandleIntent, all the incoming intents are executed on a worker thread sequentially, one after another. When an intent is processed, the next one is started automatically. Here we can do long-running work synchronously without blocking the main thread. We can send data to the service in form of intent extras and when the last intent is finished, the service stops itself and onDestroy is triggered. This means that we don’t have to call stopSelf or stopService.
In order to keep the CPU running even after the screen is turned off, we can acquire a partial wake lock in onCreate with help of the PowerManager’s newWakeLock method. In onDestroy we release this wake lock. Optionally, we can pass a long value for the timeout in milliseconds, which takes care of releasing the wake lock in case anything went wrong and release is not called. This avoids that our wake lock drains the user’s battery.
With setIntentRedelivery, we can define what should happen if the system kills the service (for example in low memory situations). A boolean value of false is the equivalent of returning START_NON_STICKY from onStartCommand in a normal service, and true equals START_REDELIVER_INTENT.
Lastly, we have to request the WAKE_LOCK and FOREGROUND_SERVICE (Android Pie) permissions in the Manifest, register our service and Application class there and call startService or ContextCompat.startForegroundService in our MainActivity to start the service.

Watch the foreground service tutorial first:
youtube.com/watch?v=FbpD5RZtbCc

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App.javaactivity_main.xmlExampleIntentService.javaMainActivity.javaAndroidManifest.xml
package com.codinginflow.intentserviceexample;

import android.app.Application;
import android.app.NotificationChannel;
import android.app.NotificationManager;
import android.os.Build;

public class App extends Application {
    public static final String CHANNEL_ID = "exampleServiceChannel";

    @Override
    public void onCreate() {
        super.onCreate();

        createNotificationChannel();
    }

    private void createNotificationChannel() {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            NotificationChannel serviceChannel = new NotificationChannel(
                    CHANNEL_ID,
                    "Example Service Channel",
                    NotificationManager.IMPORTANCE_DEFAULT
            );

            NotificationManager manager = getSystemService(NotificationManager.class);
            manager.createNotificationChannel(serviceChannel);
        }
    }
}
<?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"
    android:gravity="center"
    android:orientation="vertical"
    android:padding="16dp"
    tools:context=".MainActivity">

    <EditText
        android:id="@+id/edit_text_input"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="Input" />

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="startService"
        android:text="Start Service" />

</LinearLayout>
package com.codinginflow.intentserviceexample;

import android.app.IntentService;
import android.app.Notification;
import android.content.Intent;
import android.os.Build;
import android.os.PowerManager;
import android.os.SystemClock;
import android.support.annotation.Nullable;
import android.support.v4.app.NotificationCompat;
import android.util.Log;

import static com.codinginflow.intentserviceexample.App.CHANNEL_ID;

public class ExampleIntentService extends IntentService {
    private static final String TAG = "ExampleIntentService";

    private PowerManager.WakeLock wakeLock;

    public ExampleIntentService() {
        super("ExampleIntentService");
        setIntentRedelivery(true);
    }

    @Override
    public void onCreate() {
        super.onCreate();
        Log.d(TAG, "onCreate");

        PowerManager powerManager = (PowerManager) getSystemService(POWER_SERVICE);
        wakeLock = powerManager.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK,
                "ExampleApp:Wakelock");
        wakeLock.acquire();
        Log.d(TAG, "Wakelock acquired");

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            Notification notification = new NotificationCompat.Builder(this, CHANNEL_ID)
                    .setContentTitle("Example IntentService")
                    .setContentText("Running...")
                    .setSmallIcon(R.drawable.ic_android)
                    .build();

            startForeground(1, notification);
        }
    }

    @Override
    protected void onHandleIntent(@Nullable Intent intent) {
        Log.d(TAG, "onHandleIntent");

        String input = intent.getStringExtra("inputExtra");

        for (int i = 0; i < 10; i++) {
            Log.d(TAG, input + " - " + i);
            SystemClock.sleep(1000);
        }
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        Log.d(TAG, "onDestroy");

        wakeLock.release();
        Log.d(TAG, "Wakelock released");
    }
}

package com.codinginflow.intentserviceexample;

import android.content.Intent;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;

public class MainActivity extends AppCompatActivity {
    private EditText editTextInput;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        editTextInput = findViewById(R.id.edit_text_input);
    }

    public void startService(View v) {
        String input = editTextInput.getText().toString();

        Intent serviceIntent = new Intent(this, ExampleIntentService.class);
        serviceIntent.putExtra("inputExtra", input);

        ContextCompat.startForegroundService(this, serviceIntent);
    }
}

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

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

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

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

</manifest>