guide/components/bound-services.jd

page.title=Dch v Gn kt
parent.title=Dch v
parent.link=services.html
@jd:body


<div id="qv-wrapper">
<ol id="qv">
<h2>Trong ti liu ny</h2>
<ol>
  <li><a href="#Basics">Ni dung C bn</a></li>
  <li><a href="#Creating">To mt Dch v Gn kt</a>
    <ol>
      <li><a href="#Binder">M rng lp Trnh gn kt</a></li>
      <li><a href="#Messenger">S dng mt Hm nhn tin</a></li>
    </ol>
  </li>
  <li><a href="#Binding">Gn kt vi mt Dch v</a></li>
  <li><a href="#Lifecycle">Qun l Vng i ca mt Dch v Gn kt</a></li>
</ol>

<h2>Lp kha</h2>
<ol>
  <li>{@link android.app.Service}</li>
  <li>{@link android.content.ServiceConnection}</li>
  <li>{@link android.os.IBinder}</li>
</ol>

<h2>Mu</h2>
<ol>
  <li><a href="{@docRoot}resources/samples/ApiDemos/src/com/example/android/apis/app/RemoteService.html">{@code
      RemoteService}</a></li>
  <li><a href="{@docRoot}resources/samples/ApiDemos/src/com/example/android/apis/app/LocalService.html">{@code
      LocalService}</a></li>
</ol>

<h2>Xem thm</h2>
<ol>
  <li><a href="{@docRoot}guide/components/services.html">Dch v</a></li>
</ol>
</div>


<p>Dch v gn kt l my ch trong mt giao din my khch-my ch. Dch v gn kt cho php cc thnh phn
(chng hn nh cc hot ng) gn kt vi dch v, gi yu cu, nhn phn hi, v thm ch thc hin
truyn thng lin tin trnh (IPC). Dch v gn kt thng ch hot ng khi n phc v mt thnh phn
ng dng khc v khng chy ngm mi lin tc.</p>

<p>Ti liu ny cho bn bit cch to mt dch v gn kt, bao gm cch gn kt
vi dch v t cc thnh phn ng dng khc. Tuy nhin, bn cng nn tham kho ti liu <a href="{@docRoot}guide/components/services.html">Dch v</a>  bit thm thng tin
v cc dch v ni chung, chng hn nh cch gi thng bo t mt dch v, t
dch v  chy trong tin cnh, v nhiu ni dung khc.</p>


<h2 id="Basics">Ni dung C bn</h2>

<p>Dch v gn kt l mt s trin khai lp {@link android.app.Service} cho php
cc ng dng khc gn kt v tng tc vi n.  thc hin gn kt cho mt
dch v, bn phi trin khai phng php gi li {@link android.app.Service#onBind onBind()}. Phng php ny
tr v mt i tng {@link android.os.IBinder} nh ngha giao din lp trnh m
cc my khch c th s dng  tng tc vi dch v.</p>

<div class="sidebox-wrapper">
<div class="sidebox">
  <h3>Gn kt vi mt Dch v c Bt u</h3>

<p>Nh   cp trong ti liu <a href="{@docRoot}guide/components/services.html">Dch v</a>
, bn c th to mt dch v c bt u v gn kt. C th, dch v c th c
bt u bng cch gi {@link android.content.Context#startService startService()}, n cho php dch v
chy mi, v cng cho php mt my khch gn kt vi dch v bng cch gi {@link
android.content.Context#bindService bindService()}.
  <p>Nu bn c cho php dch v ca mnh c bt u v gn kt, th khi dch v  c
bt u, h thng s <em>khng</em> hy dch v  khi tt c my khch b gn kt. Thay vo , bn phi
dng dch v mt cch r rng bng cch gi {@link android.app.Service#stopSelf stopSelf()} hoc {@link
android.content.Context#stopService stopService()}.</p>

<p>Mc d bn nn thng xuyn trin khai hoc {@link android.app.Service#onBind onBind()}
<em>hoc</em> {@link android.app.Service#onStartCommand onStartCommand()}, i khi cn phi
trin khai c hai. V d, mt trnh chi nhc c th cho rng nn cho php dch v ca n chy
mi v cng thc hin gn kt. Bng cch ny, mt hot ng c th bt u dch v  chi vi
bn nhc v nhc tip tc chi ngay c khi ngi dng ri khi ng dng. Lc , khi ngi dng
tr li ng dng, hot ng c th gn kt vi dch v  ginh li quyn kim sot pht li.</p>

<p>m bo c phn v <a href="#Lifecycle">Qun l Vng i ca mt Dch v
Gn kt</a>  bit thm thng tin v vng i ca dch v khi thm gn kt vo mt
dch v c bt u.</p>
</div>
</div>

<p>Mt my khch c th gn kt vi dch v bng cch gi {@link android.content.Context#bindService
bindService()}. Khi lm vy, n phi cung cp vic trin khai {@link
android.content.ServiceConnection}, c chc nng theo di kt ni vi dch v. Phng php {@link
android.content.Context#bindService bindService()} tr v ngay lp tc m khng c gi tr, nhng
khi h thng Android to kt ni gia
my khch v dch v, n gi {@link
android.content.ServiceConnection#onServiceConnected onServiceConnected()} trn {@link
android.content.ServiceConnection},  giao {@link android.os.IBinder} m
my khch c th s dng  giao tip vi dch v.</p>

<p>Nhiu my khch c th kt ni vi dch v ng thi. Tuy nhin, h thng s gi phng php
{@link android.app.Service#onBind onBind()} ca dch v ca bn  truy xut {@link android.os.IBinder} ch
khi my khch u tin gn kt. Sau , h thng s giao cng mt {@link android.os.IBinder}  cho bt k
my khch b sung no c gn kt m khng gi li {@link android.app.Service#onBind onBind()}.</p>

<p>Khi my khch cui cng b gn kt vi dch v, h thng s hy dch v (tr khi dch v
cng c bt u bi {@link android.content.Context#startService startService()}).</p>

<p>Khi bn trin khai dch v gn kt ca mnh, phn quan trng nht l nh ngha giao din
m phng php gi li {@link android.app.Service#onBind onBind()} ca bn s tr v. C mt vi
cch khc nhau m bn c th nh ngha giao din {@link android.os.IBinder} ca dch v ca mnh v phn
sau y s bn v tng k thut.</p>


<h2 id="Creating">To mt Dch v Gn kt</h2>

<p>Khi to mt dch v thc hin gn kt, bn phi nu mt {@link android.os.IBinder}
cung cp giao din lp trnh m cc my khch c th s dng  tng tc vi dch v. C
ba cch bn c th nh ngha giao din:</p>

<dl>
  <dt><a href="#Binder">M rng lp Trnh gn kt</a></dt>
  <dd>Nu dch v ca bn ch ring cho ng dng ca chnh bn v chy trong cng tin trnh nh my khch
(iu ny thng hay gp), bn nn to giao din ca mnh bng cch m rng lp {@link android.os.Binder}
v tr v mt thc th ca n t
{@link android.app.Service#onBind onBind()}. My khch nhn c {@link android.os.Binder} v
c th s dng n  trc tip truy cp cc phng php cng khai c sn trong trin khai {@link android.os.Binder}
hoc thm ch trong {@link android.app.Service}.
  <p>Nn p dng k thut ny khi dch v ca bn ch l mt trnh thc hin chy ngm cho ng dng
ca chnh bn. L do duy nht bn khng nn to giao din ca mnh bng cch ny  l
dch v ca bn c s dng bi cc ng dng khc hoc gia nhng tin trnh khc nhau.</dd>

  <dt><a href="#Messenger">S dng mt Hm nhn tin</a></dt>
  <dd>Nu bn cn giao din ca mnh thc hin cc tin trnh khc nhau, bn c th to
mt giao din cho dch v bng {@link android.os.Messenger}. Bng cch ny, dch v
nh ngha mt {@link android.os.Handler} phn hi cc loi i tng {@link
android.os.Message} khc nhau. {@link android.os.Handler}
ny l c s cho mt {@link android.os.Messenger} m sau  c th chia s mt {@link android.os.IBinder}
vi my khch, cho php my khch gi lnh ti dch v bng cch s dng cc i tng {@link
android.os.Message}. Ngoi ra, my khch c th nh ngha {@link android.os.Messenger} ca
chnh n  dch v c th gi li thng bo.
  <p>y l cch n gin nht  thc hin truyn thng lin tin trnh (IPC), v {@link
android.os.Messenger} xp hng tt c yu cu thnh mt lung duy nht sao cho bn khng phi thit k
dch v ca mnh an ton vi lung.</p>
  </dd>

  <dt>S dng AIDL</dt>
  <dd>AIDL (Ngn ng nh ngha Giao din Android) thc hin tt c cng vic  phn tch i tng thnh
cc phn t m h iu hnh c th hiu c v ghp ni chng qua cc tin trnh  thc hin
IPC. Bng cch s dng {@link android.os.Messenger}, k thut trc  thc t c da trn AIDL nh l
cu trc c bn ca n. Nh   cp bn trn, {@link android.os.Messenger} to mt hng ch
gm tt c yu cu ca my khch trong mt lung duy nht, v th dch v nhn c tng yu cu mt. Tuy nhin, nu
bn mun dch v x l nhiu yu cu ng thi, bn c th s dng AIDL
trc tip. Trong trng hp ny, dch v ca bn phi c kh nng to a lung v c xy dng an ton vi lung.
  <p> s dng AIDL trc tip, bn phi
to mt tp {@code .aidl} nh ngha giao din lp trnh. Cc cng c SDK Android s dng tp
ny  khi to mt lp tm tt (abstract class) nhm trin khai giao din v x l IPC, m sau
bn c th m rng trong dch v ca mnh.</p>
  </dd>
</dl>

  <p class="note"><strong>Lu :</strong> Hu ht ng dng <strong>khng nn</strong> s dng AIDL
to mt dch v gn kt, v n c th yu cu kh nng to a lung v
c th dn n vic trin khai phc tp hn. Nh vy, AIDL khng ph hp vi hu ht ng dng
v ti liu ny khng bn v cch s dng n cho dch v ca bn. Nu bn chc chn rng mnh cn
s dng AIDL trc tip, hy xem ti liu <a href="{@docRoot}guide/components/aidl.html">AIDL</a>
.</p>


<h3 id="Binder">M rng lp Trnh gn kt</h3>

<p>Nu dch v ca bn ch c s dng bi ng dng cc b v khng cn lm vic qua nhiu tin trnh,
khi  bn c th trin khai lp {@link android.os.Binder} ca chnh mnh  cung cp quyn truy cp
trc tip cho my khch ca bn  truy nhp cc phng php cng khai trong dch v.</p>

<p class="note"><strong>Lu :</strong> Cch ny ch c tc dng nu my khch v dch v nm trong cng
ng dng v tin trnh, l trng hp ph bin nht. V d, cch ny s hot ng tt i vi mt ng dng
nhc cn gn kt mt hot ng vi dch v ca chnh n ang pht nhc
chy ngm.</p>

<p>Sau y l cch thit lp:</p>
<ol>
  <li>Trong dch v ca bn, hy to mt thc th {@link android.os.Binder} m hoc:
    <ul>
      <li>cha cc phng php cng khai m my khch c th gi</li>
      <li>tr v thc th {@link android.app.Service} hin ti, trong  c cc phng php cng khai m
my khch c th gi</li>
      <li>hoc, tr v mt thc th ca mt lp khc c lu tr bi dch v bng cc phng php cng khai m
my khch c th gi</li>
    </ul>
  <li>Tr v thc th {@link android.os.Binder} ny t phng php gi li {@link
android.app.Service#onBind onBind()}.</li>
  <li>Trong my khch, nhn {@link android.os.Binder} t phng php gi li {@link
android.content.ServiceConnection#onServiceConnected onServiceConnected()} v
thc hin gi ti dch v gn kt bng cch s dng cc phng php  nu.</li>
</ol>

<p class="note"><strong>Lu :</strong> L do dch v v my khch phi  trong cng
ng dng  l my khch c th i kiu i tng c tr v v gi cc API ca n mt cch ph hp. Dch v
v my khch cng phi  trong cng tin trnh, v k thut ny khng thc hin bt k thao tc
ghp ni qua cc tin trnh no.</p>

<p>V d, sau y l mt dch v cung cp cho my khch quyn truy cp cc phng php trong dch v thng qua
vic trin khai {@link android.os.Binder}:</p>

<pre>
public class LocalService extends Service {
    // Binder given to clients
    private final IBinder mBinder = new LocalBinder();
    // Random number generator
    private final Random mGenerator = new Random();

    /**
     * Class used for the client Binder.  Because we know this service always
     * runs in the same process as its clients, we don't need to deal with IPC.
     */
    public class LocalBinder extends Binder {
        LocalService getService() {
            // Return this instance of LocalService so clients can call public methods
            return LocalService.this;
        }
    }

    &#64;Override
    public IBinder onBind(Intent intent) {
        return mBinder;
    }

    /** method for clients */
    public int getRandomNumber() {
      return mGenerator.nextInt(100);
    }
}
</pre>

<p>{@code LocalBinder} cung cp phng php {@code getService()} cho my khch  truy xut
thc th hin ti ca {@code LocalService}. iu ny cho php my khch gi cc phng php cng khai trong
dch v. V d, my khch c th gi {@code getRandomNumber()} t dch v.</p>

<p>Sau y l mt hot ng gn kt vi {@code LocalService} v s gi {@code getRandomNumber()}
khi nhp vo nt:</p>

<pre>
public class BindingActivity extends Activity {
    LocalService mService;
    boolean mBound = false;

    &#64;Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }

    &#64;Override
    protected void onStart() {
        super.onStart();
        // Bind to LocalService
        Intent intent = new Intent(this, LocalService.class);
        bindService(intent, mConnection, Context.BIND_AUTO_CREATE);
    }

    &#64;Override
    protected void onStop() {
        super.onStop();
        // Unbind from the service
        if (mBound) {
            unbindService(mConnection);
            mBound = false;
        }
    }

    /** Called when a button is clicked (the button in the layout file attaches to
      * this method with the android:onClick attribute) */
    public void onButtonClick(View v) {
        if (mBound) {
            // Call a method from the LocalService.
            // However, if this call were something that might hang, then this request should
            // occur in a separate thread to avoid slowing down the activity performance.
            int num = mService.getRandomNumber();
            Toast.makeText(this, "number: " + num, Toast.LENGTH_SHORT).show();
        }
    }

    /** Defines callbacks for service binding, passed to bindService() */
    private ServiceConnection mConnection = new ServiceConnection() {

        &#64;Override
        public void onServiceConnected(ComponentName className,
                IBinder service) {
            // We've bound to LocalService, cast the IBinder and get LocalService instance
            LocalBinder binder = (LocalBinder) service;
            mService = binder.getService();
            mBound = true;
        }

        &#64;Override
        public void onServiceDisconnected(ComponentName arg0) {
            mBound = false;
        }
    };
}
</pre>

<p>Mu trn cho thy cch m my khch gn kt vi dch v bng cch s dng trin khai
{@link android.content.ServiceConnection} v gi li {@link
android.content.ServiceConnection#onServiceConnected onServiceConnected()}. Phn tip theo
cung cp thm thng tin v tin trnh gn kt ny vi dch v.</p>

<p class="note"><strong>Lu :</strong> V d trn khng cng khai b gn kt khi dch v,
nhng tt c my khch cn b gn kt ti mt thi im ph hp (chng hn nh khi hot ng tm dng).</p>

<p> bit thm m v d, hy xem lp <a href="{@docRoot}resources/samples/ApiDemos/src/com/example/android/apis/app/LocalService.html">{@code
LocalService.java}</a> v lp <a href="{@docRoot}resources/samples/ApiDemos/src/com/example/android/apis/app/LocalServiceActivities.html">{@code
LocalServiceActivities.java}</a> trong <a href="{@docRoot}resources/samples/ApiDemos/index.html">ApiDemos</a>.</p>


<h3 id="Messenger">S dng mt Hm nhn tin</h3>

<div class="sidebox-wrapper">
<div class="sidebox">
  <h4>So snh vi AIDL</h4>
  <p>Khi bn cn thc hin IPC, vic s dng mt {@link android.os.Messenger} cho giao din ca bn
s n gin hn so vi vic trin khai n bng AIDL, v {@link android.os.Messenger} xp hng
tt c lnh gi i vi dch v, trong khi , giao din AIDL thun ty s gi cc yu cu ng thi ti
dch v, sau  dch v phi x l to a lung.</p>
  <p>i vi hu ht ng dng, dch v khng cn thc hin to a lung, v vy s dng mt {@link
android.os.Messenger} s cho php dch v x l tng lnh gi ti mt thi im. Nu quan trng l
dch v ca bn phi c to a lung, khi  bn nn s dng <a href="{@docRoot}guide/components/aidl.html">AIDL</a>  nh ngha giao din ca mnh.</p>
</div>
</div>

<p>Nu bn cn dch v ca mnh giao tip vi cc tin trnh t xa, khi  bn c th s dng mt
{@link android.os.Messenger}  cung cp giao din cho dch v ca mnh. K thut ny cho php
bn thc hin truyn thng lin tin trnh (IPC) m khng cn s dng AIDL.</p>

<p>Sau y l tm tt cch s dng {@link android.os.Messenger}:</p>

<ul>
  <li>Dch v trin khai {@link android.os.Handler}  nhn lnh gi li cho mi
lnh gi t mt my khch.</li>
  <li>{@link android.os.Handler} c s dng  to mt i tng {@link android.os.Messenger}
(l mt tham chiu ti {@link android.os.Handler}).</li>
  <li>{@link android.os.Messenger} to mt {@link android.os.IBinder} m dch v
tr v my khch t {@link android.app.Service#onBind onBind()}.</li>
  <li>My khch s dng {@link android.os.IBinder}  khi to {@link android.os.Messenger}
(tham chiu ti {@link android.os.Handler} ca dch v), m my khch s dng  gi cc i tng
{@link android.os.Message} ti dch v.</li>
  <li>Dch v nhn c tng {@link android.os.Message} trong {@link
android.os.Handler} ca mnh&mdash;c th l theo phng php {@link android.os.Handler#handleMessage
handleMessage()}.</li>
</ul>


<p>Theo cch ny, khng c "phng php" no  my khch gi i vi dch v. Thay vo , my khch
gi thng bo (i tng {@link android.os.Message}) m dch v nhn c trong
{@link android.os.Handler} ca mnh.</p>

<p>Sau y l mt dch v v d n gin s dng mt giao din {@link android.os.Messenger}:</p>

<pre>
public class MessengerService extends Service {
    /** Command to the service to display a message */
    static final int MSG_SAY_HELLO = 1;

    /**
     * Handler of incoming messages from clients.
     */
    class IncomingHandler extends Handler {
        &#64;Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case MSG_SAY_HELLO:
                    Toast.makeText(getApplicationContext(), "hello!", Toast.LENGTH_SHORT).show();
                    break;
                default:
                    super.handleMessage(msg);
            }
        }
    }

    /**
     * Target we publish for clients to send messages to IncomingHandler.
     */
    final Messenger mMessenger = new Messenger(new IncomingHandler());

    /**
     * When binding to the service, we return an interface to our messenger
     * for sending messages to the service.
     */
    &#64;Override
    public IBinder onBind(Intent intent) {
        Toast.makeText(getApplicationContext(), "binding", Toast.LENGTH_SHORT).show();
        return mMessenger.getBinder();
    }
}
</pre>

<p>  rng phng php {@link android.os.Handler#handleMessage handleMessage()} trong
{@link android.os.Handler} l ni dch v nhn c {@link android.os.Message}
n v quyt nh vic cn lm da trn thnh vin {@link android.os.Message#what}.</p>

<p>Tt c vic m mt my khch cn lm  l to mt {@link android.os.Messenger} da trn {@link
android.os.IBinder} c dch v tr v v gi mt thng bo bng cch s dng {@link
android.os.Messenger#send send()}. V d, sau y l mt hot ng n gin gn kt vi dch v
v gi tin nhn {@code MSG_SAY_HELLO} cho dch v:</p>

<pre>
public class ActivityMessenger extends Activity {
    /** Messenger for communicating with the service. */
    Messenger mService = null;

    /** Flag indicating whether we have called bind on the service. */
    boolean mBound;

    /**
     * Class for interacting with the main interface of the service.
     */
    private ServiceConnection mConnection = new ServiceConnection() {
        public void onServiceConnected(ComponentName className, IBinder service) {
            // This is called when the connection with the service has been
            // established, giving us the object we can use to
            // interact with the service.  We are communicating with the
            // service using a Messenger, so here we get a client-side
            // representation of that from the raw IBinder object.
            mService = new Messenger(service);
            mBound = true;
        }

        public void onServiceDisconnected(ComponentName className) {
            // This is called when the connection with the service has been
            // unexpectedly disconnected -- that is, its process crashed.
            mService = null;
            mBound = false;
        }
    };

    public void sayHello(View v) {
        if (!mBound) return;
        // Create and send a message to the service, using a supported 'what' value
        Message msg = Message.obtain(null, MessengerService.MSG_SAY_HELLO, 0, 0);
        try {
            mService.send(msg);
        } catch (RemoteException e) {
            e.printStackTrace();
        }
    }

    &#64;Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }

    &#64;Override
    protected void onStart() {
        super.onStart();
        // Bind to the service
        bindService(new Intent(this, MessengerService.class), mConnection,
            Context.BIND_AUTO_CREATE);
    }

    &#64;Override
    protected void onStop() {
        super.onStop();
        // Unbind from the service
        if (mBound) {
            unbindService(mConnection);
            mBound = false;
        }
    }
}
</pre>

<p>  rng v d ny khng cho bit cch m dch v c th phn hi my khch. Nu bn mun dch v
phn hi, khi  bn cng cn to mt {@link android.os.Messenger} trong my khch. Sau
khi my khch nhn c lnh gi li {@link android.content.ServiceConnection#onServiceConnected
onServiceConnected()}, n s gi mt {@link android.os.Message} ti dch v, trong  bao gm
{@link android.os.Messenger} ca my khch trong tham s {@link android.os.Message#replyTo}
ca phng php {@link android.os.Messenger#send send()}.</p>

<p>Bn c th xem mt v d v cch cung cp tnh nng nhn tin hai chiu trong <a href="{@docRoot}resources/samples/ApiDemos/src/com/example/android/apis/app/MessengerService.html">{@code
MessengerService.java}</a> (dch v) v cc mu <a href="{@docRoot}resources/samples/ApiDemos/src/com/example/android/apis/app/MessengerServiceActivities.html">{@code
MessengerServiceActivities.java}</a> (my khch).</p>


<h2 id="Binding">Gn kt vi mt Dch v</h2>

<p>Cc thnh phn ng dng (my khch) c th gn kt vi mt dch v bng cch gi
{@link android.content.Context#bindService bindService()}. H thng Android
khi  s gi phng php {@link android.app.Service#onBind
onBind()} ca dch v, n tr v mt {@link android.os.IBinder}  tng tc vi dch v.</p>

<p>Vic gn kt din ra khng ng b. {@link android.content.Context#bindService
bindService()} tr v ngay lp tc v <em>khng</em> tr {@link android.os.IBinder} v
my khch.  nhn mt {@link android.os.IBinder}, my khch phi to mt thc th ca {@link
android.content.ServiceConnection} v chuyn n cho {@link android.content.Context#bindService
bindService()}. {@link android.content.ServiceConnection} bao gm mt phng php gi li m h thng
gi  gi {@link android.os.IBinder}.</p>

<p class="note"><strong>Lu :</strong> Ch cc hot ng, dch v, v trnh cung cp ni dung mi c th gn kt
vi mt dch v&mdash;bn <strong>khng th</strong> gn kt vi mt dch v t mt hm nhn qung b (broadcast receiver).</p>

<p>V vy,  gn kt vi mt dch v t my khch ca mnh, bn phi: </p>
<ol>
  <li>Trin khai {@link android.content.ServiceConnection}.
    <p>Vic trin khai ca bn phi khng ch hai phng php gi li:</p>
    <dl>
      <dt>{@link android.content.ServiceConnection#onServiceConnected onServiceConnected()}</dt>
        <dd>H thng gi phng php ny  gi {@link android.os.IBinder} c tr v bi
phng php {@link android.app.Service#onBind onBind()} ca dch v.</dd>
      <dt>{@link android.content.ServiceConnection#onServiceDisconnected
onServiceDisconnected()}</dt>
        <dd>H thng Android gi phng php ny khi kt ni vi dch v b mt
t ngt, chng hn nh khi dch v b li hoc b tt b. Phng php ny <em>khng</em> c gi khi
my khch b gn kt.</dd>
    </dl>
  </li>
  <li>Gi {@link
android.content.Context#bindService bindService()}, chuyn vic trin khai {@link
android.content.ServiceConnection}. </li>
  <li>Khi h thng gi phng php gi li {@link android.content.ServiceConnection#onServiceConnected
onServiceConnected()} ca bn, bn c th bt u thc hin cc lnh gi ti dch v bng cc phng php
c nh ngha bi giao din.</li>
  <li> ngt kt ni khi dch v, hy gi {@link
android.content.Context#unbindService unbindService()}.
    <p>Khi my khch ca bn b hy, n s b gn kt khi dch v, nhng bn nn lun b gn kt
khi bn  tng tc xong vi dch v hoc khi hot ng ca bn tm dng sao cho dch v c th
tt khi khng dng n. (Thi im ph hp  gn kt v b gn kt c  cp
k hn  bn di.)</p>
  </li>
</ol>

<p>V d, on m HTML sau s kt ni my khch vi dch v c to bn trn bng cch
<a href="#Binder">m rng lp Trnh gn kt</a>, v vy tt c nhng vic m n phi lm l i kiu
{@link android.os.IBinder} c tr v thnh lp {@code LocalService} v yu cu thc th {@code
LocalService}:</p>

<pre>
LocalService mService;
private ServiceConnection mConnection = new ServiceConnection() {
    // Called when the connection with the service is established
    public void onServiceConnected(ComponentName className, IBinder service) {
        // Because we have bound to an explicit
        // service that is running in our own process, we can
        // cast its IBinder to a concrete class and directly access it.
        LocalBinder binder = (LocalBinder) service;
        mService = binder.getService();
        mBound = true;
    }

    // Called when the connection with the service disconnects unexpectedly
    public void onServiceDisconnected(ComponentName className) {
        Log.e(TAG, "onServiceDisconnected");
        mBound = false;
    }
};
</pre>

<p>Vi {@link android.content.ServiceConnection} ny, my khch c th gn kt vi mt dch v bng cch chuyn
n cho {@link android.content.Context#bindService bindService()}. V d:</p>

<pre>
Intent intent = new Intent(this, LocalService.class);
bindService(intent, mConnection, Context.BIND_AUTO_CREATE);
</pre>

<ul>
  <li>Tham s u tin ca {@link android.content.Context#bindService bindService()} l mt
{@link android.content.Intent} trong  nu r tn ca cc dch v s gn kt (mc d  nh
c th ngm hiu).</li>
<li>Tham s th hai l i tng {@link android.content.ServiceConnection}.</li>
<li>Tham s th ba l mt c cho bit cc ty chn cho gn kt. Nn lun lun l {@link
android.content.Context#BIND_AUTO_CREATE}  to dch v nu n cha hot ng.
Cc gi tr c th khc l {@link android.content.Context#BIND_DEBUG_UNBIND}
v {@link android.content.Context#BIND_NOT_FOREGROUND}, hoc {@code 0} trong trng hp khng c.</li>
</ul>


<h3>Lu  b sung</h3>

<p>Sau y l mt s lu  quan trng v vic gn kt vi mt dch v:</p>
<ul>
  <li>Bn nn lun by cc li ngoi l {@link android.os.DeadObjectException} pht sinh khi
kt ni b t. y l li ngoi l duy nht pht sinh bi cc phng php t xa.</li>
  <li>Cc i tng c xem l tham chiu khp cc tin trnh. </li>
  <li>Bn nn lun ghp i gn kt v b gn kt trong khi
khp nhng khonh khc kt ni v t kt ni trong vng i ca my khch. V d:
    <ul>
      <li>Nu bn ch cn tng tc vi dch v trong khi hot ng ca bn hin th, bn
nn gn kt trong khi {@link android.app.Activity#onStart onStart()} v b gn kt trong khi {@link
android.app.Activity#onStop onStop()}.</li>
      <li>Nu bn mun hot ng ca mnh nhn c phn hi ngay c trong khi b dng khi ang
di nn, khi  bn c th gn kt trong khi {@link android.app.Activity#onCreate onCreate()} v b gn kt
trong khi {@link android.app.Activity#onDestroy onDestroy()}. Ch  rng iu ny hm  rng hot ng
ca bn cn s dng dch v trong ton b thi gian khi n ang chy (ngay c khi chy ngm), do  nu
dch v  trong mt tin trnh khc th bn hy tng trng s ca tin trnh v kh nng h thng
tt b tin trnh  s cao hn.</li>
    </ul>
    <p class="note"><strong>Lu :</strong> Thng thng bn <strong>khng</strong> nn gn kt v b gn kt
trong khi {@link android.app.Activity#onResume onResume()} v {@link
android.app.Activity#onPause onPause()} cho hot ng ca mnh, v nhng lnh gi li ny din ra ti mi thi im chuyn tip vng i
v bn nn duy tr x l ti nhng thi im chuyn tip ny  mc ti thiu. ng thi, nu
nhiu hot ng trong ng dng ca bn gn kt vi cng dch v v c s chuyn tip gia
hai trong s nhng hot ng , dch v c th b hy v to li khi hot ng hin ti b gn kt
(trong khi tm dng) trc khi hot ng tip theo gn kt (trong khi tip tc). (S chuyn tip hot ng ny i vi cch m cc hot ng
phi hp vng i ca chng c m t trong ti liu <a href="{@docRoot}guide/components/activities.html#CoordinatingActivities">Hot ng</a>
.)</p>
</ul>

<p> bit thm m v d, th hin cch gn kt vi mt dch v, hy xem lp <a href="{@docRoot}resources/samples/ApiDemos/src/com/example/android/apis/app/RemoteService.html">{@code
RemoteService.java}</a> trong <a href="{@docRoot}resources/samples/ApiDemos/index.html">ApiDemos</a>.</p>


<h2 id="Lifecycle">Qun l Vng i ca mt Dch v Gn kt</h2>

<p>Khi mt dch v b b gn kt khi tt c my khch, h thng Android s hy n (tr khi n cng
c bt u bng {@link android.app.Service#onStartCommand onStartCommand()}). Nh vy, bn khng phi
 qun l vng i dch v ca mnh nu n thun ty l mt
dch v gn kt&mdash;h thng Android s qun l n cho bn da trn vic n c gn kt vi bt k my khch no khng.</p>

<p>Tuy nhin, nu bn chn trin khai phng php gi li {@link android.app.Service#onStartCommand
onStartCommand()}, vy th bn phi dng dch v mt cch tng minh, v dch v
lc ny ang c coi l <em>c bt u</em>. Trong trng hp ny, dch v s chy cho ti khi dch v
t dng bng {@link android.app.Service#stopSelf()} hoc mt thnh phn khc s gi {@link
android.content.Context#stopService stopService()}, bt k n c gn kt vi bt k my khch
no khng.</p>

<p>Ngoi ra, nu dch v ca bn c bt u v chp nhn gn kt, lc  khi h thng gi
phng php {@link android.app.Service#onUnbind onUnbind()} ca bn, bn c th ty chn tr v
{@code true} nu bn mun nhn mt lnh gi ti {@link android.app.Service#onRebind
onRebind()} vo ln ti khi mt my khch gn kt vi dch v (thay v nhn mt lnh gi ti {@link
android.app.Service#onBind onBind()}). {@link android.app.Service#onRebind
onRebind()} s tr v rng, nhng my khch vn nhn c {@link android.os.IBinder} trong gi li
{@link android.content.ServiceConnection#onServiceConnected onServiceConnected()} ca mnh.
Hnh 1 bn di minh ha l-gic cho loi vng i ny.</p>


<img src="{@docRoot}images/fundamentals/service_binding_tree_lifecycle.png" alt="" />
<p class="img-caption"><strong>Hnh 1.</strong> Vng i ca mt dch v c bt u
v cng cho php gn kt.</p>


<p> bit thm thng tin v vng i ca mt dch v c bt u, hy xem ti liu <a href="{@docRoot}guide/components/services.html#Lifecycle">Dch v</a>.</p>