Android四大天王之Service

     本節我們學習Android四大天王的Service，如果把Activity比作是前台程序，那麼Service就是後台程序，Service的整個生命周期只會在後台執行。它一般沒有用戶操作界面，運行於系統中不容易被用戶發覺，可以用來開發如監控之類的程序。與Activity一樣，Service也是通過Intent來調用。
一、創建Service
1.繼承API的Service類[java] 
public class CustomService extends Service {...} 

public class CustomService extends Service {...}2.在AndroidManifest.xml的<application>標簽中對創建的Service進行注冊

[html]
<service android:name=".MyService" /> 

<service android:name=".MyService" />二、啟動Service

        服務不能自己運行，需要通過調用Context.startService()或Context.bindService()方法啟動服務。這兩個方法使用場合有所不同。
1.采用Context.startService()方法啟動服務
        當服務未被創建時，系統會先調用服務的onCreate()方法，接著調用onStartCommand(...)方法。如果調用startService()方法前服務已經被創建，多次調用startService()方法並不會導致多次創建服務，但會導致多次調用onStartCommand(...)方法。采用startService()方法啟動的服務，只能調用stopService()方法結束服務，服務結束時會調用onDestroy()方法。采用這種方式啟用服務，調用者與服務之間沒有關聯，即使調用者退出了，服務仍然運行。
2.采用Context.bindService()方法啟動服務
        當服務未被創建時，系統會先調用服務的onCreate()方法，接著調用onBind()方法。這個時候調用者和服務綁定在一起，調用者退出了，系統就會先調用服務的onUnbind()方法，接著調用onDestroy()方法。如果調用bindService()方法前服務已經被綁定，多次調用bindService()方法並不會導致多次創建服務及綁定(也就是說onCreate()和onBind()方法並不會被多次調用)。如果調用者希望與正在綁定的服務解除綁定，可以調用unbindService()方法，調用該方法也會導致系統調用服務的onUnbind()方法，接著調用onDestroy()方法。采用這種方式啟用服務，調用者與服務綁定在了一起，調用者一旦退出，服務也就終止。

三、Service生命周期

        既然官方沒有為Service生命周期提供示意圖，那麼我們就模仿Activity生命周期示意圖繪制一張，然後再進行總結。

 

        從上圖可以看出，其實Service的生命周期可以分為如下兩個場景：
1.由Context.startService()啟動生命周期：startService() ☞ onCreate() ☞ onStartCommand() ☞ stopService() ☞ onDestroy()
        多次調用startService()方法盡管不會多次創建服務，但onStartCommand()方法會被多次調用。
2.由Context.bindService()啟動生命周期：bindService() ☞ onCreate() ☞ onBind() ☞ unbindService() ☞ onUnbind() ☞ onDestroy()
        當調用者與服務已經綁定時，多次調用bindService()方法並不會導致onBind()方法被多次調用。
四、Service案例

1.案例代碼陳列

AndroidManifest.xml

[html]
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
    package="cn.lynn.service" 
    android:versionCode="1" 
    android:versionName="1.0" > 
 
    <uses-sdk 
        android:minSdkVersion="8" 
        android:targetSdkVersion="15" /> 
 
    <application 
        android:icon="@drawable/ic_launcher" 
        android:label="@string/app_name" > 
        <activity 
            android:name=".MainActivity" 
            android:label="@string/app_name" > 
            <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> 

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="cn.lynn.service"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="15" />

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name" >
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name" >
            <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>strings.xml

[html] 
<resources> 
    <string name="app_name">Android四大天王之Service</string> 
</resources> 

<resources>
    <string name="app_name">Android四大天王之Service</string>
</resources>main.xml[html] view plaincopyprint?
<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:orientation="vertical" > 
 
    <Button 
        android:id="@+id/btnStartMyService" 
        android:layout_width="wrap_content" 
        android:layout_height="wrap_content" 
        android:text="StartMyService" /> 
 
    <Button 
        android:id="@+id/btnStopMyService" 
        android:layout_width="wrap_content" 
        android:layout_height="wrap_content" 
        android:text="StopMyService" /> 
 
    <Button 
        android:id="@+id/btnBindMyService" 
        android:layout_width="wrap_content" 
        android:layout_height="wrap_content" 
        android:text="BindMyService" /> 
 
    <Button 
        android:id="@+id/btnUnbindMyService" 
        android:layout_width="wrap_content" 
        android:layout_height="wrap_content" 
        android:text="UnbindMyService" /> 
 
    <Button 
        android:id="@+id/btnExitActivity" 
        android:layout_width="wrap_content" 
        android:layout_height="wrap_content" 
        android:text="ExitActivity" /> 
 
</LinearLayout> 

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <Button
        android:id="@+id/btnStartMyService"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="StartMyService" />

    <Button
        android:id="@+id/btnStopMyService"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="StopMyService" />

    <Button
        android:id="@+id/btnBindMyService"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="BindMyService" />

    <Button
        android:id="@+id/btnUnbindMyService"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="UnbindMyService" />

    <Button
        android:id="@+id/btnExitActivity"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="ExitActivity" />

</LinearLayout>MainActivity.java

[java]
package cn.lynn.service; 
 
import cn.lynn.service.R; 
 
import android.app.Activity; 
import android.app.Service; 
import android.content.ComponentName; 
import android.content.Intent; 
import android.content.ServiceConnection; 
import android.os.Bundle; 
import android.os.IBinder; 
import android.util.Log; 
import android.view.View; 
import android.widget.Button; 
 
public class MainActivity extends Activity { 
    private static final String TAG = "MainActivity"; 
    Button mBtnStartMyService; 
    Button mBtnStopMyService; 
    Button mBtnBindMyService; 
    Button mBtnUnbindMyService; 
    Button mBtnExitActivity; 
 
    @Override 
    public void onCreate(Bundle savedInstanceState) { 
        super.onCreate(savedInstanceState); 
        setContentView(R.layout.main); 
        mBtnStartMyService = (Button) findViewById(R.id.btnStartMyService); 
        mBtnStartMyService.setOnClickListener(new MyOnClickListener()); 
 
        mBtnStopMyService = (Button) findViewById(R.id.btnStopMyService); 
        mBtnStopMyService.setOnClickListener(new MyOnClickListener()); 
 
        mBtnBindMyService = (Button) findViewById(R.id.btnBindMyService); 
        mBtnBindMyService.setOnClickListener(new MyOnClickListener()); 
 
        mBtnUnbindMyService = (Button) findViewById(R.id.btnUnbindMyService); 
        mBtnUnbindMyService.setOnClickListener(new MyOnClickListener()); 
 
        mBtnExitActivity = (Button) findViewById(R.id.btnExitActivity); 
        mBtnExitActivity.setOnClickListener(new MyOnClickListener()); 
    } 
 
    private ServiceConnection conn = new ServiceConnection() { 
 
        @Override 
        public void onServiceDisconnected(ComponentName name) { 
 
        } 
 
        @Override 
        public void onServiceConnected(ComponentName name, IBinder service) { 
 
        } 
    }; 
 
    class MyOnClickListener implements View.OnClickListener { 
        @Override 
        public void onClick(View v) { 
            Intent intent = new Intent(MainActivity.this, MyService.class); 
            switch (v.getId()) { 
            case R.id.btnStartMyService: 
                MainActivity.this.startService(intent); 
                break; 
            case R.id.btnStopMyService: 
                MainActivity.this.stopService(intent); 
                break; 
            case R.id.btnBindMyService: 
                MainActivity.this.bindService(intent, conn, Service.BIND_AUTO_CREATE); 
                break; 
            case R.id.btnUnbindMyService: 
                if (MyService.ServiceState.equals("onBind")) { 
                    MainActivity.this.unbindService(conn); 
                } 
                break; 
            case R.id.btnExitActivity: 
                MainActivity.this.finish(); 
                break; 
            default: 
                break; 
            } 
        } 
    } 
 
    @Override 
    protected void onDestroy() { 
        super.onDestroy(); 
        Log.i(TAG, "onDestory"); 
    } 
} 

package cn.lynn.service;

import cn.lynn.service.R;

import android.app.Activity;
import android.app.Service;
import android.content.ComponentName;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.Bundle;
import android.os.IBinder;
import android.util.Log;
import android.view.View;
import android.widget.Button;

public class MainActivity extends Activity {
    private static final String TAG = "MainActivity";
    Button mBtnStartMyService;
    Button mBtnStopMyService;
    Button mBtnBindMyService;
    Button mBtnUnbindMyService;
    Button mBtnExitActivity;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        mBtnStartMyService = (Button) findViewById(R.id.btnStartMyService);
        mBtnStartMyService.setOnClickListener(new MyOnClickListener());

        mBtnStopMyService = (Button) findViewById(R.id.btnStopMyService);
        mBtnStopMyService.setOnClickListener(new MyOnClickListener());

        mBtnBindMyService = (Button) findViewById(R.id.btnBindMyService);
        mBtnBindMyService.setOnClickListener(new MyOnClickListener());

        mBtnUnbindMyService = (Button) findViewById(R.id.btnUnbindMyService);
        mBtnUnbindMyService.setOnClickListener(new MyOnClickListener());

        mBtnExitActivity = (Button) findViewById(R.id.btnExitActivity);
        mBtnExitActivity.setOnClickListener(new MyOnClickListener());
    }

    private ServiceConnection conn = new ServiceConnection() {

        @Override
        public void onServiceDisconnected(ComponentName name) {

        }

        @Override
        public void onServiceConnected(ComponentName name, IBinder service) {

        }
    };

    class MyOnClickListener implements View.OnClickListener {
        @Override
        public void onClick(View v) {
            Intent intent = new Intent(MainActivity.this, MyService.class);
            switch (v.getId()) {
            case R.id.btnStartMyService:
                MainActivity.this.startService(intent);
                break;
            case R.id.btnStopMyService:
                MainActivity.this.stopService(intent);
                break;
            case R.id.btnBindMyService:
                MainActivity.this.bindService(intent, conn, Service.BIND_AUTO_CREATE);
                break;
            case R.id.btnUnbindMyService:
                if (MyService.ServiceState.equals("onBind")) {
                    MainActivity.this.unbindService(conn);
                }
                break;
            case R.id.btnExitActivity:
                MainActivity.this.finish();
                break;
            default:
                break;
            }
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        Log.i(TAG, "onDestory");
    }
}MyService.java

[java] 
package cn.lynn.service; 
 
import android.app.Service; 
import android.content.Intent; 
import android.os.IBinder; 
import android.util.Log; 
 
public class MyService extends Service { 
    private static final String TAG = "MyService"; 
    // 記錄Service生命周期的各個狀態  
    public static String ServiceState = ""; 
 
    @Override 
    public IBinder onBind(Intent intent) { 
        Log.i(TAG, "onBind"); 
        ServiceState = "onBind"; 
        return null; 
    } 
 
    @Override 
    public boolean onUnbind(Intent intent) { 
        super.onUnbind(intent); 
        Log.i(TAG, "onUnbind"); 
        ServiceState = "onUnbind"; 
        return false; 
    } 
 
    @Override 
    public void onCreate() { 
        super.onCreate(); 
        Log.i(TAG, "onCreate"); 
        ServiceState = "onCreate"; 
    } 
     
    @Override 
    public int onStartCommand(Intent intent, int flags, int startId) { 
        Log.i(TAG, "onStartCommand"); 
        ServiceState = "onStartCommand"; 
        return super.onStartCommand(intent, flags, startId); 
    } 
 
    @Override 
    public void onDestroy() { 
        super.onDestroy(); 
        Log.i(TAG, "onDestroy"); 
        ServiceState = "onDestroy"; 
    } 
 
} 

package cn.lynn.service;

import android.app.Service;
import android.content.Intent;
import android.os.IBinder;
import android.util.Log;

public class MyService extends Service {
    private static final String TAG = "MyService";
    // 記錄Service生命周期的各個狀態
    public static String ServiceState = "";

    @Override
    public IBinder onBind(Intent intent) {
        Log.i(TAG, "onBind");
        ServiceState = "onBind";
        return null;
    }

    @Override
    public boolean onUnbind(Intent intent) {
        super.onUnbind(intent);
        Log.i(TAG, "onUnbind");
        ServiceState = "onUnbind";
        return false;
    }

    @Override
    public void onCreate() {
        super.onCreate();
        Log.i(TAG, "onCreate");
        ServiceState = "onCreate";
    }
   
    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        Log.i(TAG, "onStartCommand");
        ServiceState = "onStartCommand";
        return super.onStartCommand(intent, flags, startId);
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        Log.i(TAG, "onDestroy");
        ServiceState = "onDestroy";
    }

}2.案例效果展示

 
 

點擊“StartMyService”按鈕，執行startService(...)方法，控制台LogCat輸出如下：

 
 

點擊“StopMyService”按鈕，執行stopService(...)方法，控制台LogCat輸出如下：

 

 
 

點擊“BindMyService”按鈕，執行bindService(...)方法，控制台LogCat輸出如下：

 

 
 

點擊“UnBindMyService”按鈕，執行unbindService(...)方法，控制台LogCat輸出如下：