【Android】接收GCM推播通知訊息

各位Android安卓開發者大家好，首先在與大家分享文章之前，小黑人在此先向大家拜個早年，祝大家新年快樂，事事順利！

哈，去年小黑人寫作文章的進度有比較緩慢一點，在此先跟大家說聲抱歉，但是我們都要向前看齊，去年已經過去了，新的一年要好好把握，所以小黑人決定今年的第一篇文章就獻給許多App軟體都必備的"推播"機制！

首先，在分享推播文章之前，我們先了解"推播"到底是什麼？
推播其實就是Google提供的GCM伺服器(Google Cloud Messaging)用來讓後端與行動裝置進行訊息的發送與接收，所以我們的手機狀態列上常常會顯示例如最新消息或優惠訊息等資訊，那我們手機端要怎麼運用GCM來接收後台發送的推播訊息呢？就讓我們繼續看下去吧～

好，在我們開始撰寫推播的接收程式前，我們要先將GCM的Library導入我們的專案中，這樣我們才可以運用GCM本身的內部推播機制，所以一開始會碰到的問題是GCM的Library在哪呢？

答案就是在"Google Play Services"裡，大家不用上網找這個Library在哪裡，其實在你的電腦裡就可以找到，首先步驟是：開啟Android SDK Manager(就是Update SDK版本的地方)，開啟後往下滑動到最底部會有一個Extras資料夾，展開Extras資料夾後裡面會有一個Google Play Services，看到這個項目就不用懷疑在左方打勾然後進行安裝就可以囉，接下來安裝下載完成後檔案會存在SDK的資料夾裡，我們再把檔案抓出來導入到我們的專案裡就完成囉。

Google Play Services的Library位置 : 你的Android SDK路徑\sdk\extras\google\google_play_services\libproject裡的google-play-services_lib專案，將這個專案import到你的專案列表裡。

目前導入google-play-services_lib專案後，這個專案和您的開發專案還沒有任何關係，所以您要在您的專案裡引用google-play-services_lib專案，步驟是：在您的專案上按右鍵，點選Properties，開啟視窗後左側列表點選Android，在下方Library區域裡按Add，將google-play-services_lib加入就可以囉。

好，前置作業都完成後，接下來就要正式開始撰寫推播的接收程式囉！

1. 首先，開啟AndroidManifest.xml進行撰寫，加入下方的權限設定與Application內的資訊。(其實Google有提供GCM的實作範例，裡面範例都寫的很清楚，小黑人也是跟著範例實作)

權限部分加入 : 
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.GET_ACCOUNTS" />
<uses-permission android:name="android.permission.WAKE_LOCK" />
<permission android:name="您的Package Name.permission.C2D_MESSAGE" android:protectionLevel="signature" />
<uses-permission android:name="您的Package Name.permission.C2D_MESSAGE" />
<uses-permission android:name="com.google.android.c2dm.permission.RECEIVE" />

Application內加入 : 
<meta-data android:name="com.google.android.gms.version" android:value="@integer/google_play_services_version" />

<receiver
android:name=".GcmBroadcastReceiver"
android:permission="com.google.android.c2dm.permission.SEND"
>
    <intent-filter>
        <action android:name="com.google.android.c2dm.intent.RECEIVE" />
        <category android:name="您的Package Name" />
    </intent-filter>
</receiver>
        
<service android:name=".GcmIntentService" />

放入這些程式碼，AndroidManifest的部分就完成囉！

2. 建立GcmBroadcastReceiver.java，這個class算是在接收GCM的呼叫，收到通知後啟動Service。
public class GcmBroadcastReceiver extends WakefulBroadcastReceiver
{
    @Override
    public void onReceive(Context context, Intent intent) 
    {
        ComponentName comp = new ComponentName(context.getPackageName(), GcmIntentService.class.getName());
        startWakefulService(context, (intent.setComponent(comp)));
        setResultCode(Activity.RESULT_OK);
    }
}

3. 建立GcmIntentService.java，這個class算是收到GCM的呼叫通知後，解析傳來的通知訊息。
public class GcmIntentService extends IntentService 
{
    public static final int NOTIFICATION_ID = 1;
    private NotificationManager mNotificationManager;
    NotificationCompat.Builder builder;
    public static final String TAG = "GCM Demo";

    public GcmIntentService() 
    {
        super("GcmIntentService");
    }

    @Override
    protected void onHandleIntent(Intent intent)
    {
        //解析收到的文字訊息再傳入sendNotification進行顯示
        Bundle extras = intent.getExtras();
        GoogleCloudMessaging gcm = GoogleCloudMessaging.getInstance(this);
        String messageType = gcm.getMessageType(intent);

        if (!extras.isEmpty()) 
        {  
            if (GoogleCloudMessaging.MESSAGE_TYPE_SEND_ERROR.equals(messageType)) 
            {
                sendNotification("Send error: " + extras.toString());
            } 
            else if (GoogleCloudMessaging.MESSAGE_TYPE_DELETED.equals(messageType)) 
            {
                sendNotification("Deleted messages on server: " + extras.toString());
            }
            else if (GoogleCloudMessaging.MESSAGE_TYPE_MESSAGE.equals(messageType)) 
            {
                for (int i = 0; i < 5; i++)
                {
                    Log.i(TAG, "Working... " + (i + 1) + "/5 @ " + SystemClock.elapsedRealtime());
                           
                    try 
                    {
                        Thread.sleep(5000);
                    }
                    catch (InterruptedException e) 
                    {
                    }
                }
                Log.i(TAG, "Completed work @ " + SystemClock.elapsedRealtime());
                sendNotification("Received: " + extras.toString());
                Log.i(TAG, "Received: " + extras.toString());
            }
        }
        GcmBroadcastReceiver.completeWakefulIntent(intent);
    }

    //設定Notification要顯示的資訊與點擊Notification要開啟的頁面
    private void sendNotification(String msg) 
    {
        mNotificationManager = (NotificationManager) this.getSystemService(Context.NOTIFICATION_SERVICE);        
        PendingIntent contentIntent = PendingIntent.getActivity(this, 0,new Intent(this, MainActivity.class) , 0);

        NotificationCompat.Builder mBuilder =
        new NotificationCompat.Builder(this)
        .setSmallIcon(R.drawable.ic_launcher)
        .setContentTitle("要顯示的標題名稱")
        .setStyle(new NotificationCompat.BigTextStyle()
        .bigText(msg))
        .setContentText(msg);
        
        mBuilder.setContentIntent(contentIntent);
        mNotificationManager.notify(NOTIFICATION_ID, mBuilder.build());
    }
}

4. 最後一個步驟，上方新增的兩個class都是屬於接收到訊息後要做的事，現在這個步驟是要向GCM註冊這支行動裝置，如果沒有註冊這個動作的話，GCM根本不知道要向哪個行動裝置進行推播發送，所以向GCM註冊裝置是一個很重要的環節。

首先在要做註冊的Activity裡添加註冊程式碼，小黑人以MainActivity作為範例。

public class MainActivity extends Activity 
{
    //只要把您的GCM註冊ID填入，其他部分皆一樣
    private String SENDER_ID = "您GCM的註冊ID";
    private static final String TAG = "GCM :";
    public static final String EXTRA_MESSAGE = "message";
    public static final String PROPERTY_REG_ID = "registration_id";
    private static final String PROPERTY_APP_VERSION = "appVersion";
    private static final int PLAY_SERVICES_RESOLUTION_REQUEST = 9000;
    private GoogleCloudMessaging gcm;
    private AtomicInteger msgId = new AtomicInteger();
    private Context context = this;
    private String regid;
    
        @Override
        protected void onCreate(Bundle savedInstanceState) 
        {
                super.onCreate(savedInstanceState);
                setContentView(R.layout.main);
                
                //確認是否已註冊過裝置，將這段放入您欲註冊的位置
                if (checkPlayServices()) 
                {
                    gcm = GoogleCloudMessaging.getInstance(this);
                    regid = getRegistrationId(context);

                   if (regid.isEmpty()) 
                   {
                        registerInBackground();
                   }
                }
                else 
                {
                    Log.i(TAG, "No valid Google Play Services APK found.");
                }
        }
        
        private boolean checkPlayServices() 
        {
            int resultCode = GooglePlayServicesUtil.isGooglePlayServicesAvailable(this);
        
            if (resultCode != ConnectionResult.SUCCESS) 
            {
                if (GooglePlayServicesUtil.isUserRecoverableError(resultCode)) 
                {
                    GooglePlayServicesUtil.getErrorDialog(resultCode, this,PLAY_SERVICES_RESOLUTION_REQUEST).show(); 
                } 
                else
                {
                    Log.i(TAG, "This device is not supported.");
                    finish();
                }
                return false;
            }
            return true;
        }
    
    private void storeRegistrationId(Context context, String regId) 
    {
        final SharedPreferences prefs = getGcmPreferences(context);
        int appVersion = getAppVersion(context);
        Log.i(TAG, "Saving regId on app version " + appVersion);
        SharedPreferences.Editor editor = prefs.edit();
        editor.putString(PROPERTY_REG_ID, regId);
        editor.putInt(PROPERTY_APP_VERSION, appVersion);
        editor.commit();
    }
    
    private String getRegistrationId(Context context) 
    {
        final SharedPreferences prefs = getGcmPreferences(context);
        String registrationId = prefs.getString(PROPERTY_REG_ID, "");
        
        if (registrationId.isEmpty()) 
        {
            Log.i(TAG, "Registration not found.");
            return "";
        } 
        int registeredVersion = prefs.getInt(PROPERTY_APP_VERSION, Integer.MIN_VALUE);
        int currentVersion = getAppVersion(context);
        if (registeredVersion != currentVersion) 
        {
            Log.i(TAG, "App version changed.");
            return "";
        }
        return registrationId;
    }
    
    private void registerInBackground() 
    {
        new AsyncTask<Void, Void, String>() 
        {
            @Override
            protected String doInBackground(Void... params) 
            {
                String msg = "";
                try 
                {
                    if (gcm == null) 
                    {
                        gcm = GoogleCloudMessaging.getInstance(context);
                    }
                    regid = gcm.register(SENDER_ID);
                    
                    msg = "Device registered, registration ID=" + regid;

                    sendRegistrationIdToBackend();
                    storeRegistrationId(context, regid);
                }
                catch (IOException ex) 
                {
                    msg = "Error :" + ex.getMessage();
                }
                return msg;
            }

            @Override
            protected void onPostExecute(String msg) 
            {
            }
        }.execute(null, null, null);
    }
    
    private static int getAppVersion(Context context)
    {
        try 
        {
            PackageInfo packageInfo = context.getPackageManager().getPackageInfo(context.getPackageName(), 0);
                   
            return packageInfo.versionCode;
        } 
        catch (NameNotFoundException e) 
        {
            throw new RuntimeException("Could not get package name: " + e);
        }
    }
    
    private SharedPreferences getGcmPreferences(Context context) 
    {
        return getSharedPreferences(MainActivity.class.getSimpleName(), Context.MODE_PRIVATE);      
    }
    
    private void sendRegistrationIdToBackend() 
    {
        //裝置向GCM註冊完畢時進入
    }
} 

以上為行動裝置向GCM註冊的分享文章，跟Google提供的範例程式一樣，小黑人也只是把程式碼貼上而已，只需要把GCM ID更換和註冊完畢後要做的動作變更，其他部分皆沒有修改。

以上4大步驟就是行動裝置接收GCM推播訊息的流程，雖然整體看起來蠻多程式碼的，但是需要修改的程式碼卻只有一小部分，大部分都只要將程式碼貼上即可，註冊動作與接收動作完成就可以收到GCM的推播通知囉，大家可以試試看在App裡加入推播機制～

謝謝大家，如有任何問題都可以和小黑人一起交流討論！

☆小黑人☆