405 lines
8.3 KiB
Markdown
405 lines
8.3 KiB
Markdown
# Service详解
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## 目录
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- [Service生命周期](#service生命周期)
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- [Service类型](#service类型)
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- [IntentService](#intentservice)
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- [Service与Activity通信](#service与activity通信)
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- [Service保活](#service保活)
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- [Service最佳实践](#service最佳实践)
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- [面试常见问题](#面试常见问题)
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---
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## Service生命周期
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### 普通 Service 生命周期
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```java
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public class MyService extends Service {
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@Override
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public void onCreate() {
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super.onCreate();
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// Service 创建时调用
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}
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@Override
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public int onStartCommand(Intent intent, int flags, int startId) {
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// Service 启动时调用（startService）
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return START_STICKY;
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}
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@Override
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public IBinder onBind(Intent intent) {
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// Service 绑定时调用（bindService）
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return binder;
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}
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@Override
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public void onDestroy() {
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super.onDestroy();
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// Service 销毁时调用
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}
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}
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```
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### 绑定 Service 生命周期
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```java
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// 绑定 Service
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bindService(intent, serviceConnection, Context.BIND_AUTO_CREATE);
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// 解绑 Service
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unbindService(serviceConnection);
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// 生命周期
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// onCreate() → onBind() → onUnbind() → onDestroy()
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```
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---
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## Service类型
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### 1. 普通 Service
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```java
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// 普通 Service：后台执行任务
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public class MyService extends Service {
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@Override
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public int onStartCommand(Intent intent, int flags, int startId) {
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// 执行任务
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new Thread(() -> {
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// 耗时操作
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}).start();
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return START_STICKY;
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}
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@Override
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public IBinder onBind(Intent intent) {
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return null;
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}
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}
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```
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### 2. 前台 Service
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```java
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// 前台 Service：显示通知
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public class ForegroundService extends Service {
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@Override
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public void onCreate() {
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super.onCreate();
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Notification notification = new NotificationCompat.Builder(this, CHANNEL_ID)
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.setContentTitle("服务运行中")
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.setContentText("正在执行任务")
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.setSmallIcon(R.drawable.ic_notification)
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.build();
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startForeground(1, notification);
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}
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}
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```
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### 3. 绑定 Service
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```java
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// 绑定 Service：与 Activity 通信
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public class BoundService extends Service {
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private IBinder binder = new LocalBinder();
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public class LocalBinder extends Binder {
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BoundService getService() {
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return BoundService.this;
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}
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}
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@Override
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public IBinder onBind(Intent intent) {
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return binder;
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}
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public void doSomething() {
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// Service 方法
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}
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}
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// Activity 中使用
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private ServiceConnection connection = new ServiceConnection() {
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@Override
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public void onServiceConnected(ComponentName name, IBinder service) {
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BoundService.LocalBinder binder = (BoundService.LocalBinder) service;
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boundService = binder.getService();
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}
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@Override
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public void onServiceDisconnected(ComponentName name) {
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boundService = null;
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}
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};
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```
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---
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## IntentService
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### IntentService 特点
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```java
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// IntentService：自动在后台线程执行任务
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public class MyIntentService extends IntentService {
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public MyIntentService() {
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super("MyIntentService");
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}
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@Override
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protected void onHandleIntent(Intent intent) {
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// 在后台线程执行
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// 任务执行完毕后自动停止
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String action = intent.getAction();
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if ("ACTION_DOWNLOAD".equals(action)) {
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downloadFile();
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}
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}
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}
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// 启动
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Intent intent = new Intent(this, MyIntentService.class);
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intent.setAction("ACTION_DOWNLOAD");
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startService(intent);
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```
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### IntentService vs Service
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| 特性 | Service | IntentService |
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|------|---------|---------------|
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| 线程 | 主线程 | 后台线程 |
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| 自动停止 | 否 | 是 |
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| 多任务 | 需要手动处理 | 自动排队 |
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| 适用场景 | 需要长期运行 | 一次性任务 |
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---
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## Service与Activity通信
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### 方式1：Binder
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```java
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// Service
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public class MyService extends Service {
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private IBinder binder = new LocalBinder();
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public class LocalBinder extends Binder {
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MyService getService() {
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return MyService.this;
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}
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}
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@Override
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public IBinder onBind(Intent intent) {
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return binder;
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}
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public void doWork() {
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// Service 方法
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}
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}
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// Activity
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private ServiceConnection connection = new ServiceConnection() {
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@Override
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public void onServiceConnected(ComponentName name, IBinder service) {
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MyService.LocalBinder binder = (MyService.LocalBinder) service;
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myService = binder.getService();
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myService.doWork();
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}
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@Override
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public void onServiceDisconnected(ComponentName name) {
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myService = null;
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}
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};
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bindService(intent, connection, Context.BIND_AUTO_CREATE);
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```
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### 方式2：BroadcastReceiver
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```java
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// Service 发送广播
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Intent broadcast = new Intent("ACTION_UPDATE");
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broadcast.putExtra("data", "value");
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sendBroadcast(broadcast);
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// Activity 接收广播
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private BroadcastReceiver receiver = new BroadcastReceiver() {
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@Override
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public void onReceive(Context context, Intent intent) {
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String data = intent.getStringExtra("data");
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}
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};
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registerReceiver(receiver, new IntentFilter("ACTION_UPDATE"));
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```
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### 方式3：Messenger
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```java
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// Service
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public class MessengerService extends Service {
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private Messenger messenger = new Messenger(new Handler() {
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@Override
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public void handleMessage(Message msg) {
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// 处理消息
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}
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});
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@Override
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public IBinder onBind(Intent intent) {
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return messenger.getBinder();
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}
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}
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// Activity
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private Messenger serviceMessenger;
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private ServiceConnection connection = new ServiceConnection() {
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@Override
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public void onServiceConnected(ComponentName name, IBinder service) {
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serviceMessenger = new Messenger(service);
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Message msg = Message.obtain();
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msg.what = 1;
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msg.obj = "Data";
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try {
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serviceMessenger.send(msg);
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} catch (RemoteException e) {
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e.printStackTrace();
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}
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}
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@Override
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public void onServiceDisconnected(ComponentName name) {
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serviceMessenger = null;
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}
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};
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```
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---
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## Service保活
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### 保活方式
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#### 1. 前台 Service
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```java
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// 使用前台 Service
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startForeground(1, notification);
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```
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#### 2. 双进程守护
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```java
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// 两个进程互相守护
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// 进程1：主进程
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// 进程2：守护进程
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```
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#### 3. JobScheduler
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```java
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// 使用 JobScheduler 定时启动
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JobInfo jobInfo = new JobInfo.Builder(1, componentName)
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.setPeriodic(15 * 60 * 1000)
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.build();
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jobScheduler.schedule(jobInfo);
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```
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### 注意事项
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```java
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// ❌ 不推荐：过度保活
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// 1. 影响用户体验
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// 2. 消耗电量
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// 3. 可能被系统杀死
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// ✅ 推荐：合理使用
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// 1. 使用前台 Service（重要任务）
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// 2. 使用 JobScheduler（定时任务）
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// 3. 使用 WorkManager（后台任务）
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```
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---
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## Service最佳实践
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### 1. 及时停止 Service
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```java
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// 任务完成后及时停止
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@Override
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protected void onHandleIntent(Intent intent) {
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// 执行任务
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doWork();
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// 任务完成后自动停止
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}
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```
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### 2. 避免内存泄漏
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```java
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@Override
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public void onDestroy() {
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super.onDestroy();
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// 释放资源
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if (handler != null) {
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handler.removeCallbacksAndMessages(null);
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}
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}
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```
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### 3. 合理选择 Service 类型
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```java
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// 长期运行 → 前台 Service
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// 一次性任务 → IntentService
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// 需要通信 → 绑定 Service
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```
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---
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## 面试常见问题
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### Q1: Service 生命周期？
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**答案：**
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- **启动 Service**：onCreate() → onStartCommand() → onDestroy()
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- **绑定 Service**：onCreate() → onBind() → onUnbind() → onDestroy()
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### Q2: Service 和 Thread 的区别？
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**答案：**
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- **Service**：运行在主线程，是 Android 组件
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- **Thread**：后台线程，不是 Android 组件
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- **使用**：Service 中创建 Thread 执行耗时操作
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### Q3: IntentService 的特点？
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**答案：**
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1. 自动在后台线程执行
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2. 任务执行完毕后自动停止
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3. 多个任务自动排队执行
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### Q4: Service 保活方式？
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**答案：**
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1. 前台 Service
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2. 双进程守护
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3. JobScheduler
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4. WorkManager
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---
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*最后更新：2024年*
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