[安藤]android 如何讓你的service永不停止

在android的世界裡面，service的設計的幾個難關：

1. static的參考不見的時候該怎麼辦
2. 傳進來的intent是null的時候該怎麼辦
3. service被系統kill掉之後該怎麼辦

下面的範例程式碼來說明。

public class ChachaService extends Service  {
    private Context mContext;
    private ContentResolver mResolver;
    private SharedPreferences mPref;
    private String savedParameters;
    public void onCreate() {
    // TODO Auto-generated method stub
        super.onCreate();
        mContext = getApplicationContext();  //系統資料是安全的. 
        mResolver = getContentResolver();  //系統資料是安全的. 所以在這裡也可以存取database.
        mPref = getSharedPreferences("Prefs", 0);  //安全. 建議在onDestroy裡面實作儲存parameter的動作，並在這裡回復。
        savedParameters = mPref.getString("savedparameter", "aaaa");

        IntentFilter filter = new IntentFilter();
        filter.addAction(WifiManager.NETWORK_STATE_CHANGED_ACTION);
        registerReceiver(mReceiver, filter);    //broadcast receiver 也安全。
    }

    public int onStartCommand(Intent intent, int flags, int startId) {
        // TODO Auto-generated method stub
        super.onStartCommand(intent, flags, startId);
        //注意！ 被系統low memory killed 並重啓的時候， intent為null!
        //! boolean bool = intent.getBooleanExtra("xxxx", false);
        return START_STICKY;  //回傳此值才能讓系統幫你在資源允許的時候自動回復service。
    }

    private BroadcastReceiver mReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {
       ...
    }

    public void onDestroy() {
    // TODO Auto-generated method stub
        super.onDestroy();
        if (mReceiver != null)
            unregisterReceiver(mReceiver);
        Editor editor = mPref.edit();
        editor.putString("savedparameter", savedParameters);
        editor.commit();
    }

}