使用BroadcastReceiver的Android IntentService

In this tutorial, we’ll be discussing one of the fundamental components of the Android framework, namely IntentService. We’ll be developing an Android IntentService application using BroadcastReceiver.

在本教程中，我们将讨论Android框架的基本组件之一，即IntentService。我们将使用BroadcastReceiver开发一个Android IntentService应用程序。

Android IntentService (Android IntentService)

We’ve discussed Android Service in earlier tutorial. An IntentService extends the Service class.

我们在前面的教程中讨论了Android Service 。 IntentService扩展了Service类。

Both Services and IntentServices are used to run operations that do not need a UI.

Services和IntentServices都用于运行不需要UI的操作。

An IntentService is used to run data sequentially. Each time you call an Intent to the Service, that operation would be added into the queue.

IntentService用于顺序运行数据。每次您对服务调用Intent时，该操作都会添加到队列中。

Android IntentService与服务 (Android IntentService vs Service)

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A Service is invoked using startService()	An IntentService is invoked using Intent.
A Service can be invoked from any thread.	An IntentService can in invoked from the Main thread only.
A Service runs background operations on the Main Thread of the Application by default. Hence it can block your Application’s UI.	An IntentService creates a separate worker thread to run background operations.
A Service invoked multiple times would create multiple instances.	An IntentService invoked multiple times won’t create multiple instances.
A service needs to be stopped using stopSelf() or stopService()	An IntentService automatically stops after the queue is completed. No need to trigger stopService() or stopSelf().
Android service can run parallel operations.	In an IntentService, multiple intent calls are automatically Queued and they would be executed sequentially. An IntentService cannot run parallel operation like a Service.

使用startService（）调用服务	使用Intent调用IntentService。
可以从任何线程调用服务。	IntentService只能从Main线程中调用。
默认情况下，服务在应用程序的主线程上运行后台操作。因此，它可以阻止您的应用程序的UI。	IntentService创建一个单独的工作线程来运行后台操作。
多次调用的服务将创建多个实例。	多次调用的IntentService不会创建多个实例。
需要使用stopSelf（）或stopService（）停止服务	队列完成后，IntentService自动停止。无需触发stopService（）或stopSelf（）。
Android服务可以运行并行操作。	在IntentService中，多个intent调用会自动排队，并且将按顺序执行。 IntentService不能像Service一样运行并行操作。

In a service, the onHandleIntent() method gets invoked when the intent is passed from the activity.

在服务中，当从活动传递意图时，将调用onHandleIntent()方法。

BroadcastReceivers are used to transfer messages across applications or between a service and an activity.
To transfer data between a service and an activity we need to use a LocalBroadcastManager.

BroadcastReceivers用于在应用程序之间或服务与活动之间传输消息。
为了在服务和活动之间传输数据，我们需要使用LocalBroadcastManager 。

LocalBroadcastManager class comes with the support library and is used to transfer data locally only.
You cannot transfer data outside the application.

支持库随附LocalBroadcastManager类，该类仅用于本地传输数据。
您无法在应用程序外部传输数据。

In the following section, we’ll create an application that passes a string to the IntentService which returns it to the Activity after a delay. Thanks to IntentService, this happens sequentially.

在下一节中，我们将创建一个应用程序，该应用程序将字符串传递给IntentService，并在延迟后将其返回给Activity。多亏了IntentService，这是顺序发生的。

Android IntentService示例项目结构 (Android IntentService Example Project Structure)

布局代码 (Layout code)

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="https://schemas.android.com/apk/res/android"xmlns:app="https://schemas.android.com/apk/res-auto"xmlns:tools="https://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"tools:context=".MainActivity"><EditTextandroid:id="@+id/inputText"android:layout_width="match_parent"android:layout_height="wrap_content"android:layout_margin="8dp"android:hint="Enter your message"app:layout_constraintBottom_toBottomOf="parent"app:layout_constraintLeft_toLeftOf="parent"app:layout_constraintRight_toRightOf="parent"app:layout_constraintTop_toTopOf="parent" /><Buttonandroid:id="@+id/button"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_marginTop="8dp"android:text="Send Message"app:layout_constraintEnd_toEndOf="parent"app:layout_constraintStart_toStartOf="parent"app:layout_constraintTop_toBottomOf="@+id/inputText" /><TextViewandroid:id="@+id/textView"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_marginTop="24dp"android:text="Message received from the Service is:\n"app:layout_constraintEnd_toEndOf="parent"app:layout_constraintStart_toStartOf="parent"app:layout_constraintTop_toTopOf="parent" /></android.support.constraint.ConstraintLayout>

The code for the MainActivity.java class is given below:

MainActivity.java类的代码如下：

package com.journaldev.androidintentservices;import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.support.v4.content.LocalBroadcastManager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;public class MainActivity extends AppCompatActivity {TextView textView;Button button;EditText editText;MyReceiver myReceiver;public static final String FILTER_ACTION_KEY = "any_key";@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);textView = findViewById(R.id.textView);button = findViewById(R.id.button);editText = findViewById(R.id.inputText);button.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {String message = editText.getText().toString();Intent intent = new Intent(MainActivity.this, MyService.class);intent.putExtra("message", message);startService(intent);}});}private void setReceiver() {myReceiver = new MyReceiver();IntentFilter intentFilter = new IntentFilter();intentFilter.addAction(FILTER_ACTION_KEY);LocalBroadcastManager.getInstance(this).registerReceiver(myReceiver, intentFilter);}@Overrideprotected void onStart() {setReceiver();super.onStart();}@Overrideprotected void onStop() {unregisterReceiver(myReceiver);super.onStop();}private class MyReceiver extends BroadcastReceiver {@Overridepublic void onReceive(Context context, Intent intent) {String message = intent.getStringExtra("broadcastMessage");textView.setText(textView.getText() + "\n" + message);}}
}

Some important points:

一些要点：

We need to set an IntentFilter to register our BroadcastReceiver.我们需要设置一个IntentFilter来注册我们的BroadcastReceiver。
Inside the IntentFilter Action we specify a string.在IntentFilter Action内部，我们指定一个字符串。
The same string would be used in our IntentService as well.同样的字符串也将在我们的IntentService中使用。
We must unregister our BroadcastReceiver in the onStop() method.我们必须在onStop()方法中取消注册BroadcastReceiver。
LocalBroadcastManager instance is used to set the receiver.LocalBroadcastManager实例用于设置接收方。
Our BroadcastReceiver would append the string returned from the service.我们的BroadcastReceiver将附加从服务返回的字符串。

The code for MyService.java class is given below:

MyService.java类的代码如下：

package com.journaldev.androidintentservices;import android.app.IntentService;
import android.content.Intent;
import android.os.SystemClock;
import android.support.v4.content.LocalBroadcastManager;public class MyService extends IntentService {public MyService() {super("MyService");}@Overrideprotected void onHandleIntent(Intent intent) {String message = intent.getStringExtra("message");intent.setAction(MainActivity.FILTER_ACTION_KEY);SystemClock.sleep(3000);String echoMessage = "IntentService after a pause of 3 seconds echoes " + message;LocalBroadcastManager.getInstance(getApplicationContext()).sendBroadcast(intent.putExtra("broadcastMessage", echoMessage));}
}

To return the data to the activity we use the sendBroadcast method. It passes the data to the BroadcastReceiver. The BroadcastReceiver eventually passes the data to the Activity.

要将数据返回到活动，我们使用sendBroadcast方法。它将数据传递到BroadcastReceiver。广播接收器最终将数据传递给活动。

You must declare the Service inside the Manifest file. Without the LocalBroadcastManager the above data won’t be passed.

您必须在清单文件中声明服务。如果没有LocalBroadcastManager，则不会传递上述数据。

The output of the above application in action is given below:

上面应用程序的输出如下：

This brings an end to this tutorial. You can download the project from the link below.

本教程到此结束。您可以从下面的链接下载项目。

Download Android IntentService Project下载Android IntentService项目

GitHub Repository.GitHub Repository下载项目代码。

翻译自: https://www.journaldev.com/20735/android-intentservice-broadcastreceiver