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IntentService

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IntentService是什麼?


IntentService是Service的一種，使用上較為方便簡單。其背景執行方式是透過 HandleThread，因此單個IntentService上的任務是循序執行的，可以保證執行緒安全。不同的IntentService在執行上也不會互相干擾。

IntentService適合用於客戶端不須和Service互動的情況下，基本上由客戶端呼叫startService並指定啟動的IntentService。



簡單的IntentService實作


public class SimpleIntentService extends IntentService {  
    
    public SimpleIntentService() {  
      super("SimpleIntentService");  
    }  
    
    @Override  
    protected void onHandleIntent(Intent intent) {  
    }  
    
  }

onHandleIntent方法會執行在新的執行緒上，也是放置耗時操作的位置。其參數intent就是從客戶端傳遞過來的intent。

另外需要在AndroidManifest.xml宣告該IntentService 
<service  
    android:exported="false"  
    android:name=".simpleintentservice.SimpleIntentService">  
  </service>

android:exported="false"代表是否可以由其他的App啟動。



啟動IntentService


客戶端透過呼叫startService方法來啟動IntentService 
public class SimpleIntentServiceActivity extends AppCompatActivitye {  
    
    @Override  
    protected void onCreate(Bundle savedInstanceState) {  
      super.onCreate(savedInstanceState);  
      setContentView(R.layout.activity_simple_intent_service);  
    
      Intent launchSimpleIntentService = new Intent(this, SimpleIntentService.class);  
      startService(launchSimpleIntentService);  
    }  
  }




客戶端傳遞資料到IntentService


從客戶端透過intent放置資料便可傳遞到IntentService 
Intent launchSimpleIntentService = new Intent(this, SimpleIntentService.class);  
  launchSimpleIntentService.putExtra("data", "data from activity");  
  startService(launchSimpleIntentService);

透過IntentService的onHandleIntent的參數取出資料 
@Override  
  protected void onHandleIntent(Intent intent) {  
    String data = intent.getStringExtra("data");  
    Log.d(TAG, "data:" + data);  
  }

output: 
D: data:data from activity




IntentService的生命週期


複寫IntentService的生命週期方法觀察呼叫順序 
public class SimpleIntentService extends IntentService {  
    
    private static final String TAG = SimpleIntentService.class.getSimpleName();  
    
    public SimpleIntentService() {  
      super("SimpleIntentService");  
      Log.d(TAG, "SimpleIntentService: ");  
    }  
    
    @Override  
    public void onCreate() {  
      super.onCreate();  
      Log.d(TAG, "onCreate: ");  
    }  
    
    @Override  
    public void onDestroy() {  
      super.onDestroy();  
      Log.d(TAG, "onDestroy: ");  
    }  
    
    @Override  
    public int onStartCommand(@Nullable Intent intent, int flags, int startId) {  
      Log.d(TAG, "onStartCommand: ");  
      return super.onStartCommand(intent, flags, startId);  
    }  
    
    @Override  
    protected void onHandleIntent(Intent intent) {  
      Log.d(TAG, "onHandleIntent: ");  
      String data = intent.getStringExtra("data");  
      Log.d(TAG, "data:" + data);  
    }  
    
  }

Client call 
Intent launchSimpleIntentService = new Intent(this, SimpleIntentService.class);  
  launchSimpleIntentService.putExtra("data", "data from activity");  
  startService(launchSimpleIntentService);  
  Log.d(TAG, "startService");

Output 
D/SimpleIntentServiceActivity: startService  
  D/SimpleIntentService: SimpleIntentService:   
  D/SimpleIntentService: onCreate:   
  D/SimpleIntentService: onStartCommand:   
  D/SimpleIntentService: onHandleIntent:   
  D/SimpleIntentService: data:data from activity  
  D/SimpleIntentService: onDestroy:

從Output觀察IntentService生命週期的順序為
建構式 -> onCreate -> onStartCommand -> onHandleIntent -> onDestroy



客戶端停止IntentService


透過呼叫stopService()方法來停止IntentService。 
Intent stopSimpleIntentService = new Intent(this, SimpleIntentService.class);  
  stopService(stopSimpleIntentService);  
  Log.d(TAG, "stopService");

傳入的Intent必須指定要停止的IntentService。

呼叫StopService之後，IntentService便會呼叫onDestroy方法銷毀自己。

需要注意的是因為onHandleIntent方法內部是由新的執行緒來執行，因此即使是客戶端呼叫了stopService，但是onHandleIntent方法不會結束。

為了測試這點在onHandleIntent方法加入計時10秒的操作 
@Override  
  protected void onHandleIntent(Intent intent) {  
    Log.d(TAG, "onHandleIntent: ");  
    String data = intent.getStringExtra("data");  
    Log.d(TAG, "data:" + data);  
    sleep(10);  
  }  
    
  private void sleep(int sleepTimeSeconds) {  
    for (int i = 0; i < sleepTimeSeconds; ++i) {  
      try {  
        Thread.sleep(1000);  
      } catch (InterruptedException e) {  
        e.printStackTrace();  
      }  
      Log.d(TAG, "sleep: "+i);  
    }  
  }

客戶端並在第3秒呼叫stopService

Output如下 
D/SimpleIntentServiceActivity: startService  
  D/SimpleIntentService: SimpleIntentService:   
  D/SimpleIntentService: onCreate:   
  D/SimpleIntentService: onStartCommand:   
  D/SimpleIntentService: onHandleIntent:   
  D/SimpleIntentService: data:data from activity  
  D/SimpleIntentService: sleep: 0  
  D/SimpleIntentService: sleep: 1  
  D/SimpleIntentService: sleep: 2  
  D/SimpleIntentService: sleep: 3  
  D/SimpleIntentServiceActivity: stopService  
  D/SimpleIntentService: onDestroy:   
  D/SimpleIntentService: sleep: 4  
  D/SimpleIntentService: sleep: 5  
  D/SimpleIntentService: sleep: 6  
  D/SimpleIntentService: sleep: 7  
  D/SimpleIntentService: sleep: 8  
  D/SimpleIntentService: sleep: 9

可以看到即使IntentService已經銷毀了，但計時仍然繼續。

因此若要呼叫stopService也一併停止onHandleIntent的內容，可以建立成員變數來控制是否要停止計時，如下 
private boolean mIsDestroy;  
    
  @Override  
  public void onDestroy() {  
    mIsDestroy = true;  
    super.onDestroy();  
    Log.d(TAG, "onDestroy: ");  
  }  
    
  private void sleep(int sleepTimeSeconds) {  
    for (int i = 0; i < sleepTimeSeconds && !mIsDestroy; ++i) {  
      try {  
        Thread.sleep(1000);  
      } catch (InterruptedException e) {  
        e.printStackTrace();  
      }  
      Log.d(TAG, "sleep: "+i);  
    }  
  }




IntentService的循序


IntentService在單一執行緒上執行任務，若客戶端呼叫多次startService方法，IntentService也會保持等待當前的任務完成後再執行下一個任務。

修改印出耗時資訊時也印出IntentService toString 
  private void sleep(int sleepTimeSeconds) {  
      for (int i = 0; i < sleepTimeSeconds && !mIsDestroy; ++i) {  
        try {  
          Thread.sleep(1000);  
        } catch (InterruptedException e) {  
          e.printStackTrace();  
        }  
        Log.d(TAG, "sleep: "+i+" name:"+toString());  
      }  
    }

連續啟動3次IntentService，Outout如下 
D/SimpleIntentService: SimpleIntentService:   
  D/SimpleIntentService: onCreate:   
  D/SimpleIntentService: onStartCommand:   
  D/SimpleIntentService: onHandleIntent:   
  D/SimpleIntentService: data:data from activity  
  D/SimpleIntentService: onStartCommand:   
  D/SimpleIntentService: onStartCommand:   
  D/SimpleIntentService: sleep: 0 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 1 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 2 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 3 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 4 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 5 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 6 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 7 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 8 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 9 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: onHandleIntent:   
  D/SimpleIntentService: data:data from activity  
  D/SimpleIntentService: sleep: 0 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 1 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 2 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 3 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 4 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 5 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 6 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 7 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 8 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 9 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: onHandleIntent:   
  D/SimpleIntentService: data:data from activity  
  D/SimpleIntentService: sleep: 0 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 1 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 2 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 3 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 4 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 5 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 6 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 7 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 8 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: sleep: 9 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@369cf9c  
  D/SimpleIntentService: onDestroy:

可以看到每個任務都必須等到上一個任務完成後才執行。



不同IntentService執行


觀察不同的IntentService執行的情況
新增另一個IntentService為AnotherSimpleIntentService如下 
public class AnotherSimpleIntentService extends IntentService {  
    
    private static final String TAG = AnotherSimpleIntentService.class.getSimpleName();  
    
    private boolean mIsDestroy;  
    
    public AnotherSimpleIntentService() {  
      super("AnotherSimpleIntentService");  
      Log.d(TAG, "AnotherSimpleIntentService: ");  
    }  
    
    @Override  
    public void onCreate() {  
      super.onCreate();  
      Log.d(TAG, "onCreate: ");  
    }  
    
    @Override  
    public void onDestroy() {  
      mIsDestroy = true;  
      super.onDestroy();  
      Log.d(TAG, "onDestroy: ");  
    }  
    
    @Override  
    public int onStartCommand(@Nullable Intent intent, int flags, int startId) {  
      Log.d(TAG, "onStartCommand: ");  
      return super.onStartCommand(intent, flags, startId);  
    }  
    
    @Override  
    protected void onHandleIntent(Intent intent) {  
      Log.d(TAG, "onHandleIntent: ");  
      String data = intent.getStringExtra("data");  
      Log.d(TAG, "data:" + data);  
      sleep(10);  
    }  
    
    private void sleep(int sleepTimeSeconds) {  
      for (int i = 0; i < sleepTimeSeconds && !mIsDestroy; ++i) {  
        try {  
          Thread.sleep(1000);  
        } catch (InterruptedException e) {  
          e.printStackTrace();  
        }  
        Log.d(TAG, "sleep: "+i+" name:"+toString());  
      }  
    }  
    
  }

AndroidManifest.xml宣告AnotherSimpleIntentService 
    <service  
        android:exported="false"  
        android:name=".simpleintentservice.AnotherSimpleIntentService">  
      </service>

在客戶端依序啟動SimpleIntentService和AnotherSimpleIntentService 
  public void onClick(View view) {  
      int uiID = view.getId();  
      switch (uiID) {  
        case R.id.start_intent_service:  
          startSimpleIntentService();  
          startAnotherSimpleIntentService();  
          break;  
      }  
    }  
    
    private void startAnotherSimpleIntentService() {  
      Intent launchAnotherSimpleIntentService = new Intent(this, AnotherSimpleIntentService.class);  
      launchAnotherSimpleIntentService.putExtra("data", "data from activity");  
      startService(launchAnotherSimpleIntentService);  
      Log.d(TAG, "startService");  
    }  
    
    private void startSimpleIntentService() {  
      Intent launchSimpleIntentService = new Intent(this, SimpleIntentService.class);  
      launchSimpleIntentService.putExtra("data", "data from activity");  
      startService(launchSimpleIntentService);  
      Log.d(TAG, "startService");  
    }

Output如下 
D/SimpleIntentServiceActivity: startService  
  D/SimpleIntentServiceActivity: startService  
  D/SimpleIntentService: SimpleIntentService:   
  D/SimpleIntentService: onCreate:   
  D/SimpleIntentService: onStartCommand:   
  D/SimpleIntentService: onHandleIntent:   
  D/SimpleIntentService: data:data from activity  
  D/AnotherSimpleIntentService: AnotherSimpleIntentService:   
  D/AnotherSimpleIntentService: onCreate:   
  D/AnotherSimpleIntentService: onStartCommand:   
  D/AnotherSimpleIntentService: onHandleIntent:   
  D/AnotherSimpleIntentService: data:data from activity  
  D/SimpleIntentService: sleep: 0 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@ff71da5  
  D/AnotherSimpleIntentService: sleep: 0 name:com.codefoxx.serviceexample.simpleintentservice.AnotherSimpleIntentService@9de157a  
  D/SimpleIntentService: sleep: 1 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@ff71da5  
  D/AnotherSimpleIntentService: sleep: 1 name:com.codefoxx.serviceexample.simpleintentservice.AnotherSimpleIntentService@9de157a  
  D/SimpleIntentService: sleep: 2 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@ff71da5  
  D/AnotherSimpleIntentService: sleep: 2 name:com.codefoxx.serviceexample.simpleintentservice.AnotherSimpleIntentService@9de157a  
  D/SimpleIntentService: sleep: 3 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@ff71da5  
  D/AnotherSimpleIntentService: sleep: 3 name:com.codefoxx.serviceexample.simpleintentservice.AnotherSimpleIntentService@9de157a  
  D/SimpleIntentService: sleep: 4 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@ff71da5  
  D/AnotherSimpleIntentService: sleep: 4 name:com.codefoxx.serviceexample.simpleintentservice.AnotherSimpleIntentService@9de157a  
  D/SimpleIntentService: sleep: 5 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@ff71da5  
  D/AnotherSimpleIntentService: sleep: 5 name:com.codefoxx.serviceexample.simpleintentservice.AnotherSimpleIntentService@9de157a  
  D/SimpleIntentService: sleep: 6 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@ff71da5  
  D/AnotherSimpleIntentService: sleep: 6 name:com.codefoxx.serviceexample.simpleintentservice.AnotherSimpleIntentService@9de157a  
  D/SimpleIntentService: sleep: 7 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@ff71da5  
  D/AnotherSimpleIntentService: sleep: 7 name:com.codefoxx.serviceexample.simpleintentservice.AnotherSimpleIntentService@9de157a  
  D/SimpleIntentService: sleep: 8 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@ff71da5  
  D/AnotherSimpleIntentService: sleep: 8 name:com.codefoxx.serviceexample.simpleintentservice.AnotherSimpleIntentService@9de157a  
  D/SimpleIntentService: sleep: 9 name:com.codefoxx.serviceexample.simpleintentservice.SimpleIntentService@ff71da5  
  D/SimpleIntentService: onDestroy:   
  D/AnotherSimpleIntentService: sleep: 9 name:com.codefoxx.serviceexample.simpleintentservice.AnotherSimpleIntentService@9de157a  
  D/AnotherSimpleIntentService: onDestroy:

可以看到不同的IntentService彼此不會互相影響，各自執行任務。

 
Orignal From: IntentService

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Error: Default interface methods are only supported starting with Android N (--min-api 24)

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這是在 Android Studio 中套用了 androidx.core 之後出現的問題，build project 出現以下錯誤: 
Error: Default interface methods are only supported starting with Android N (--min-api 24): android.view.MenuItem androidx.core.internal.view.SupportMenuItem.setContentDescription(java.lang.CharSequence)

解決方法有 2 種:
1. 在 /app/build.gradle 修改 minSdkVersion 為 24 
android {  
      ...  
      defaultConfig {  
          ...  
          minSdkVersion 24  
          ...  
      }  
      ...  
  }

 

2.在 /app/build.gradle 加入以下內容 
android {  
     ...  
      compileOptions {  
          sourceCompatibility = '1.8'  
          targetCompatibility = '1.8'  
      }  
     ...  
  }

 
Orignal From: Error: Default interface methods are only supported starting with Android N (--min-api 24)

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