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 Android教程網 >> Android技術 >> 關於Android編程 >> Android開發學習之路--Service之初體驗

Android開發學習之路--Service之初體驗

編輯：關於Android編程

android最後一個組件便是service了，終於學習到最後一個組件了，從年前的開發環境的搭建，到現在學到最後一個組件花了三周的時間，期間記錄的點點滴滴，照著書本學習編寫的代碼都受益匪淺，這裡要感謝第一行代碼這本書。三個星期除了三十和初一沒有學習，其余時間堅持每天學習一個知識點，總算慢慢地學習了個大概，接下去繼續學習其他的東西。說了這麼多還是開始學習Service組件吧。

Service從字面上理解就是服務的意思，也就是為應用程序提供服務，比如我們在播放一首歌的時候，我又想把它下載下來，那麼我們就可以把他交給Service去處理。播放歌曲是在後台運行的，那麼它也是個服務，還是來個例子吧。先新建工程ServiceTest。編寫布局如下：

<!--{cke_protected}{C}%3C!%2D%2D%3Fxml%20version%3D%221.0%22%20encoding%3D%22utf-8%22%3F%2D%2D%3E-->
<linearlayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" android:layout_margin="10dp" android:padding="10dp" tools:context="com.example.jared.servicetest.MainActivity"><button android:id="@+id/startService" android:text="啟動Service" android:layout_width="match_parent" android:layout_height="wrap_content" android:textallcaps="false"></button><button android:id="@+id/stopService" android:text="停止Service" android:layout_width="match_parent" android:layout_height="wrap_content" android:textallcaps="false"></button></linearlayout>
這裡實現了兩個按鈕啟動和停止Service。接著新建一個MyService類，繼承Service，代碼如下： 
package com.example.jared.servicetest;

import android.app.Service;
import android.content.Intent;
import android.os.IBinder;
import android.support.annotation.Nullable;
import android.util.Log;
import android.widget.Toast;

/**
 * Created by jared on 16/2/18.
 */
public class MyService extends Service{

    private static final String TAG = "MyService";

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }

    @Override
    public void onCreate() {
        super.onCreate();
        Log.d(TAG, "onCreate is called");
        Toast.makeText(MyService.this, "onCreate is called",Toast.LENGTH_SHORT).show();
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        Log.d(TAG, "onStartCommand is called");
        Toast.makeText(MyService.this, "onStartCommand is called",Toast.LENGTH_SHORT).show();
        return super.onStartCommand(intent, flags, startId);
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        Log.d(TAG, "onDestroy is called");
        Toast.makeText(MyService.this, "onDestroy is called",Toast.LENGTH_SHORT).show();
    }
}
這裡重寫了onCreate方法，onStartCommand方法和onDestroy方法，這裡在各個方法裡加了些調試信息，接著我們再實現MainActivity的代碼： 
package com.example.jared.servicetest;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    private Button mStartServiceBtn;
    private Button mStopServiceBtn;

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

        mStartServiceBtn = (Button)findViewById(R.id.startService);
        mStopServiceBtn = (Button)findViewById(R.id.stopService);

        mStartServiceBtn.setOnClickListener(new myOnClickListener());
        mStopServiceBtn.setOnClickListener(new myOnClickListener());
    }

    private class myOnClickListener implements View.OnClickListener {
        @Override
        public void onClick(View view) {
            switch (view.getId()) {
                case R.id.startService:
                    Intent mStartIntent = new Intent(getApplicationContext(), MyService.class);
                    startService(mStartIntent);
                    break;
                case R.id.stopService:
                    Intent mSopIntent = new Intent(getApplicationContext(), MyService.class);
                    stopService(mSopIntent);
                    break;
                default:
                    break;
            }
        }
    }
}

這裡當按start的時候啟動service，按stop的按鈕的時候停止服務。先來運行下看下效果，先啟動Service吧，效果如下：

\ \
 

從上可知先調用了onCreate方法，然後調用onStartCommand方法。然後我們看下在運行著的服務，打開手機的setting下的apps裡的running：

\

從圖可知ServiceTest已經在了，然後這個時候我們再點擊啟動Service的話，是不會再調用onCreate方法的，只會調用onStartCommand方法，只有stop了Service才可以，那我們先stop掉Service，效果如下：

\

如圖調用了onDestroy方法。接著再啟動Service的話，就和上述一樣了。

上面代碼中還有個方法那就是onBind方法了，從字面可以理解到這個方法是把Activity和Service綁定了，那樣就可以通過Activity控制Service了。下面實現下代碼，修改layout如下：

<!--{cke_protected}{C}%3C!%2D%2D%3Fxml%20version%3D%221.0%22%20encoding%3D%22utf-8%22%3F%2D%2D%3E-->
<linearlayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical" android:layout_margin="10dp" android:padding="10dp" tools:context="com.example.jared.servicetest.MainActivity"><button android:id="@+id/startService" android:text="啟動Service" android:layout_width="match_parent" android:layout_height="wrap_content" android:textallcaps="false"></button><button android:id="@+id/stopService" android:text="停止Service" android:layout_width="match_parent" android:layout_height="wrap_content" android:textallcaps="false"></button><button android:id="@+id/startDownloadService" android:text="綁定Service Download" android:layout_width="match_parent" android:layout_height="wrap_content" android:textallcaps="false"></button><button android:id="@+id/stopDownloadService" android:text="解綁Service Download" android:layout_width="match_parent" android:layout_height="wrap_content" android:textallcaps="false"></button><button android:id="@+id/startGetProgressService" android:text="綁定Service GetProgress" android:layout_width="match_parent" android:layout_height="wrap_content" android:textallcaps="false"></button><button android:id="@+id/stopGetProgressService" android:text="解綁Service GetProgress" android:layout_width="match_parent" android:layout_height="wrap_content" android:textallcaps="false"></button></linearlayout>

這裡添加了啟動下載的服務和獲取當前下載狀態的服務。Service中添加Binder，代碼如下： 
package com.example.jared.servicetest;

import android.app.Service;
import android.content.Intent;
import android.os.Binder;
import android.os.IBinder;
import android.support.annotation.Nullable;
import android.util.Log;
import android.widget.Toast;

/**
 * Created by jared on 16/2/18.
 */
public class MyService extends Service{

    private static final String TAG = "MyService";

    private DownloadBinder mDownloadBinder = new DownloadBinder();

    class DownloadBinder extends Binder {
        private int progress = 0;
        public void startDownload() {
            Log.d(TAG, "startDownload is called");
            Toast.makeText(MyService.this, "startDownload is called",Toast.LENGTH_SHORT).show();
            progress = 0;
            new Thread(new Runnable(){
                @Override
                public void run() {
                    for (int i=0; i<=100; i++) {
                        try {
                            Thread.sleep(1000);
                            progress++;
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                }
            }).start();
        }
        public int getProgress() {
            Log.d(TAG, "getProgress is called");
            Toast.makeText(MyService.this, "getProgress is called",Toast.LENGTH_SHORT).show();
            return progress;
        }
    }

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return mDownloadBinder;
    }

    @Override
    public void onCreate() {
        super.onCreate();
        Log.d(TAG, "onCreate is called");
        Toast.makeText(MyService.this, "onCreate is called",Toast.LENGTH_SHORT).show();
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        Log.d(TAG, "onStartCommand is called");
        Toast.makeText(MyService.this, "onStartCommand is called",Toast.LENGTH_SHORT).show();
        return super.onStartCommand(intent, flags, startId);
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        Log.d(TAG, "onDestroy is called");
        Toast.makeText(MyService.this, "onDestroy is called",Toast.LENGTH_SHORT).show();
    }
}

這裡模擬了一個下載的過程，啟動下載後，線程每秒更新個數值，然後可以通過getProgress去獲取數值。接著修改MainActivity代碼如下： 
package com.example.jared.servicetest;

import android.content.ComponentName;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.Bundle;
import android.os.IBinder;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {

    private Button mStartServiceBtn;
    private Button mStopServiceBtn;
    private Button mBindService1Btn;
    private Button mUnbindService1Btn;
    private Button mBindService2Btn;
    private Button mUnbindService2Btn;

    private MyService.DownloadBinder downloadBinder;

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

        mStartServiceBtn = (Button)findViewById(R.id.startService);
        mStopServiceBtn = (Button)findViewById(R.id.stopService);
        mBindService1Btn = (Button)findViewById(R.id.startDownloadService);
        mUnbindService1Btn = (Button)findViewById(R.id.stopDownloadService);
        mBindService2Btn = (Button)findViewById(R.id.startGetProgressService);
        mUnbindService2Btn = (Button)findViewById(R.id.stopGetProgressService);

        mStartServiceBtn.setOnClickListener(new myOnClickListener());
        mStopServiceBtn.setOnClickListener(new myOnClickListener());
        mBindService1Btn.setOnClickListener(new myOnClickListener());
        mUnbindService1Btn.setOnClickListener(new myOnClickListener());
        mBindService2Btn.setOnClickListener(new myOnClickListener());
        mUnbindService2Btn.setOnClickListener(new myOnClickListener());
    }

    private class myOnClickListener implements View.OnClickListener {
        @Override
        public void onClick(View view) {
            switch (view.getId()) {
                case R.id.startService:
                    Intent mStartIntent = new Intent(getApplicationContext(), MyService.class);
                    startService(mStartIntent);
                    break;
                case R.id.stopService:
                    Intent mSopIntent = new Intent(getApplicationContext(), MyService.class);
                    stopService(mSopIntent);
                    break;
                case R.id.startDownloadService:
                    Intent mBindIntent = new Intent(getApplicationContext(), MyService.class);
                    bindService(mBindIntent, startDownloadInService, BIND_AUTO_CREATE);
                    break;
                case R.id.stopDownloadService:
                    unbindService(startDownloadInService);
                    break;
                case R.id.startGetProgressService:
                    Intent mGetProgress = new Intent(getApplicationContext(), MyService.class);
                    bindService(mGetProgress, getProgressInService, BIND_AUTO_CREATE);
                    break;
                case R.id.stopGetProgressService:
                    unbindService(getProgressInService);
                    break;
                default:
                    break;
            }
        }
    }

    private ServiceConnection startDownloadInService = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName componentName, IBinder iBinder) {
            downloadBinder = (MyService.DownloadBinder)iBinder;
            downloadBinder.startDownload();
        }

        @Override
        public void onServiceDisconnected(ComponentName componentName) {

        }
    };

    private ServiceConnection getProgressInService = new ServiceConnection() {
        @Override
        public void onServiceConnected(ComponentName componentName, IBinder iBinder) {
            downloadBinder = (MyService.DownloadBinder)iBinder;
            String progressValue = String.valueOf(downloadBinder.getProgress());
            Toast.makeText(getApplicationContext(), "ProgressNow is:"+progressValue, Toast.LENGTH_SHORT).show();
        }

        @Override
        public void onServiceDisconnected(ComponentName componentName) {

        }
    };
}
這裡實例化了ServiceConnection，當通過bindService方法的時候，會通過ServiceConnection的onServiceConnected方法來調用Service中剛創建的下載類的方法。運行看下效果，先啟動下載，再獲取progress，運行效果如下：

\\\

這裡要注意的是，服務是單例的，所謂單例就是只有一個實例，只能被new一次，不同進程也只能調用一次。當我們調用bind download的時候會直接調用Service的onCreate，當我們解綁的時候，也會調用Service的onDestroy方法。不過當我們調用了啟動Service，又調用了binder的話，那就得ubind和stop方法都得調用。

上述當我們獲取progress的時候，如果不解綁，那麼之後的都是無效的。只有獲取了一次，解綁了，再獲取才有效。

android系統當內存不夠的時候會自動回收優先級比較低的服務，所以為了讓服務可以一直保存運行狀態，而不會由於內存不足的原因導致被回收，就需要使用前台服務。前台服務就是一直運行並在狀態欄顯示，類似音樂播放器就會在狀態欄一直保存著。簡單修改Service代碼如下：

package com.example.jared.servicetest;

import android.app.PendingIntent;
import android.app.Service;
import android.content.Intent;
import android.os.Binder;
import android.os.IBinder;
import android.support.annotation.Nullable;
import android.support.v4.app.NotificationCompat;
import android.util.Log;
import android.widget.Toast;

/**
 * Created by jared on 16/2/18.
 */
public class MyService extends Service{

    private static final String TAG = "MyService";
    private static final int NOTIFICATION_ID = 1;

    private DownloadBinder mDownloadBinder = new DownloadBinder();

    class DownloadBinder extends Binder {
        private int progress = 0;
        public void startDownload() {
            Log.d(TAG, "startDownload is called");
            Toast.makeText(MyService.this, "startDownload is called",Toast.LENGTH_SHORT).show();
            progress = 0;
            new Thread(new Runnable(){
                @Override
                public void run() {
                    for (int i=0; i<=100; i++) {
                        try {
                            Thread.sleep(1000);
                            progress++;
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                }
            }).start();
        }
        public int getProgress() {
            Log.d(TAG, "getProgress is called");
            Toast.makeText(MyService.this, "getProgress is called",Toast.LENGTH_SHORT).show();
            return progress;
        }
    }

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return mDownloadBinder;
    }

    @Override
    public void onCreate() {
        super.onCreate();
        Log.d(TAG, "onCreate is called");
        Toast.makeText(MyService.this, "onCreate is called",Toast.LENGTH_SHORT).show();
        NotificationCompat.Builder notification = new NotificationCompat.Builder(this);
        notification.setSmallIcon(R.mipmap.ic_launcher);
        notification.setContentTitle("前台服務");
        notification.setContentText("這是個前台服務");
        Intent intent = new Intent(this, MainActivity.class);
        PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, intent, 0);
        notification.setContentIntent(pendingIntent);
        startForeground(NOTIFICATION_ID, notification.build());
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        Log.d(TAG, "onStartCommand is called");
        Toast.makeText(MyService.this, "onStartCommand is called",Toast.LENGTH_SHORT).show();
        return super.onStartCommand(intent, flags, startId);
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        Log.d(TAG, "onDestroy is called");
        Toast.makeText(MyService.this, "onDestroy is called",Toast.LENGTH_SHORT).show();
        stopForeground(true);
    }
}
這裡用到了notification，然後通過startForegroid方法來啟動一個前台服務，運行看下效果：

\\ \

從上圖可知，當啟動了前台服務的時候，在狀態欄有個圖標顯示，當activity退出的時候，還是存在，只有當停止服務的時候才消失，那麼就可以理解了為什麼qq音樂退出了還在播放歌曲，還可以通過前台服務點擊進入app。其實就是這個道理了。

關於Service就先學習到這裡了。總算把Service學習好了。接下去繼續學習別的知識點了。

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