xref: /frameworks/base/docs/html-intl/intl/vi/guide/components/services.jd

page.title=Dch v
@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>
<ol>
  <li><a href="#Declaring">Khai bo mt dch v trong bn k khai</a></li>
</ol>
<li><a href="#CreatingAService">To mt Dch v c Bt u</a>
  <ol>
    <li><a href="#ExtendingIntentService">M rng lp IntentService</a></li>
    <li><a href="#ExtendingService">M rng lp Dch v</a></li>
    <li><a href="#StartingAService">Bt u mt dch v</a></li>
    <li><a href="#Stopping">Dng mt dch v</a></li>
  </ol>
</li>
<li><a href="#CreatingBoundService">To mt Dch v Gn kt</a></li>
<li><a href="#Notifications">Gi Thng bo ti Ngi dng</a></li>
<li><a href="#Foreground">Chy mt Dch v trong Tin cnh</a></li>
<li><a href="#Lifecycle">Qun l Vng i ca mt Dch v</a>
<ol>
  <li><a href="#LifecycleCallbacks">Trin khai gi li vng i</a></li>
</ol>
</li>
</ol>

<h2>Lp kha</h2>
<ol>
  <li>{@link android.app.Service}</li>
  <li>{@link android.app.IntentService}</li>
</ol>

<h2>Mu</h2>
<ol>
  <li><a href="{@docRoot}resources/samples/ApiDemos/src/com/example/android/apis/app/ServiceStartArguments.html">{@code
      ServiceStartArguments}</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/bound-services.html">Dch v Gn kt</a></li>
</ol>

</div>


<p>{@link android.app.Service} l mt thnh phn ng dng c kh nng thc hin
cc thao tc chy ko di trong nn v khng cung cp giao din ngi dng. Mt
thnh phn ng dng khc c th bt u mt dch v v n s tip tc chy ngm ngay c khi ngi dng
chuyn sang mt ng dng khc. Ngoi ra, mt thnh phn c th gn kt vi mt dch v 
tng tc vi n v thm ch thc hin truyn thng lin tin trnh (IPC). V d, mt dch v c th
x l cc giao dch mng, pht nhc, thc hin I/O tp, hoc tng tc vi mt trnh cung cp ni dung, tt c
u xut pht t nn.</p>

<p>V c bn, mt dch v c th c hai dng:</p>

<dl>
  <dt>c bt u</dt>
  <dd>Dch v c dng "c bt u" khi mt thnh phn ng dng (chng hn nh mt hot ng) bt u n bng cch
gi {@link android.content.Context#startService startService()}. Sau khi c bt u, dch v
c th chy ngm v thi hn, ngay c khi thnh phn bt u n b hy. Thng thng,
dch v c bt u s thc hin mt thao tc n l v khng tr v kt qu cho hm gi.
V d, n c th ti xung hoc ti ln mt tp thng qua mng. Khi thao tc c hon thnh, dch v
t n s dng li.</dd>
  <dt>Gn kt</dt>
  <dd>Dch v c dng "gn kt" khi mt thnh phn ng dng gn kt vi n bng cch gi {@link
android.content.Context#bindService bindService()}. Dch v gn kt s a ra
mt giao din my khch-my ch cho php cc thnh phn tng tc vi dch v, gi yu cu, nhn kt qu, v thm ch
lm vy thng qua truyn thng lin tin trnh (IPC). Dch v gn kt ch chy trong khi
mt thnh phn ng dng khc c gn kt vi n. Nhiu thnh phn c th gn kt cng lc vi dch v,
nhng khi tt c b b gn kt th dch v s b hy.</dd>
</dl>

<p>Mc d ti liu ny thng  cp ti hai loi dch v ring r, dch v
ca bn c th hot ng theo c hai cch&mdash;n c th c bt u ( chy v thi hn) v cng cho php gn kt.
 n gin l vn  bn c trin khai mt cp phng php gi li hay khng: {@link
android.app.Service#onStartCommand onStartCommand()}  cho php thnh phn bt u n v {@link
android.app.Service#onBind onBind()}  cho php n gn kt.</p>

<p>Khng ph thuc vo vic ng dng ca bn c bt u, gn kt, hay c hai, bt k thnh phn ng dng no
cng c th s dng dch v (thm ch t mt ng dng ring bit), ging nh cch m bt k thnh phn no cng c th s dng
mt hot ng&mdash;bng cch bt u n bng mt {@link android.content.Intent}. Tuy nhin, bn c th khai bo
dch v l ring t trong tp bn k khai, v chn truy cp t cc ng dng khc. iu ny
c trnh by k hn trong phn v <a href="#Declaring">Khai bo dch v trong
bn k khai</a>.</p>

<p class="caution"><strong>Ch :</strong> Mt dch v chy trong
lung chnh ca tin trnh lu tr ca n&mdash;dch v <strong>khng</strong> to lung ca chnh n
v <strong>khng</strong> chy trong mt tin trnh ring bit (tr khi bn quy nh khc). iu ny c ngha
l, nu dch v ca bn nh thc hin bt k cng vic nng no i vi CPU hay chn cc thao tc (chng hn nh pht li MP3
hay kt ni mng), bn nn to mt lung mi bn trong dch v  thc hin cng vic . Bng cch s dng
mt lung ring bit, bn s gim ri ro gp li ng dng Khng Hi p (ANR) v lung chnh ca ng dng c th
vn dnh ring cho tng tc gia ngi dng vi cc hot ng ca bn.</p>


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

<div class="sidebox-wrapper">
<div class="sidebox">
  <h3>Bn nn s dng dch v hay lung?</h3>
  <p>Dch v n thun l mt thnh phn c th chy ngm ngay c khi ngi dng khng
ang tng tc vi ng dng ca bn. V th, bn ch nn to mt dch v nu  l iu bn
cn.</p>
  <p>Nu bn cn thc hin cng vic bn ngoi lung chnh ca mnh, nhng ch trong khi ngi dng ang tng tc vi
ng dng ca bn, th thay vo , bn nn to mt lung mi ch khng phi mt dch v. V
d, nu bn mun pht mt bn nhc, nhng ch trong khi hot ng ca bn ang chy, bn c th to
mt lung trong {@link android.app.Activity#onCreate onCreate()}, bt u chy n trong {@link
android.app.Activity#onStart onStart()}, ri dng n trong {@link android.app.Activity#onStop
onStop()}. Cng xem xt vic s dng {@link android.os.AsyncTask} hoc {@link android.os.HandlerThread},
thay v s dng lp {@link java.lang.Thread} truyn thng. Xem ti liu <a href="{@docRoot}guide/components/processes-and-threads.html#Threads">Tin trnh v
Lung</a>  bit thm thng tin v lung.</p>
  <p>Hy nh rng nu bn s dng mt dch v, n vn chy trong lung chnh ca ng dng ca bn theo
mc nh, v th bn vn nn to mt lung mi trong dch v nu n thc hin cc thao tc tng cng hoc
chn.</p>
</div>
</div>

<p> to mt dch v, bn phi to mt lp con ca {@link android.app.Service} (hoc mt
trong cc lp con hin ti ca n). Trong trin khai ca mnh, bn cn khng ch mt s phng php gi li c chc nng
x l nhng kha cnh chnh trong vng i ca dch v v cung cp mt c ch  cc thnh phn gn kt vi
dch v , nu ph hp. Nhng phng php gi li quan trng nht m bn nn khng ch l:</p>

<dl>
  <dt>{@link android.app.Service#onStartCommand onStartCommand()}</dt>
    <dd>H thng s gi phng php ny khi mt thnh phn khc, chng hn nh mt hot ng,
yu cu dch v phi c bt u, bng cch gi {@link android.content.Context#startService
startService()}. Sau khi phng php ny thc thi, dch v s c bt u v c th chy v thi hn trong
nn. Nu bn trin khai iu ny, bn c trch nhim dng dch v khi
cng vic ca n c hon thnh, bng cch gi {@link android.app.Service#stopSelf stopSelf()} hoc {@link
android.content.Context#stopService stopService()}. (Nu ch mun cung cp kh nng gn kt, bn khng
cn trin khai phng php ny.)</dd>
  <dt>{@link android.app.Service#onBind onBind()}</dt>
    <dd>H thng s gi phng php ny khi mt thnh phn khc mun gn kt vi
dch v (chng hn nh  thc hin RPC), bng cch gi {@link android.content.Context#bindService
bindService()}. Trong trin khai phng php ny ca mnh, bn phi cung cp mt giao din m cc my khch
s dng  giao tip vi dch v, bng cch tr v {@link android.os.IBinder}. Bn phi lun
trin khai phng php ny, nhng nu bn khng mun cho php gn kt th bn nn tr v rng.</dd>
  <dt>{@link android.app.Service#onCreate()}</dt>
    <dd>H thng s gi phng php ny khi dch v c to lp ln u,  thc hin quy trnh thit lp mt ln
(trc khi n c th gi hoc {@link android.app.Service#onStartCommand onStartCommand()} hoc
{@link android.app.Service#onBind onBind()}). Nu dch v  ang chy, phng php ny s khng c
gi.</dd>
  <dt>{@link android.app.Service#onDestroy()}</dt>
    <dd>H thng s gi phng php ny khi dch v khng cn c s dng v ang b hy.
Dch v ca bn s trin khai phng php ny  dn dp mi ti nguyn nh lung, i tng theo di
c ng k, hm nhn, v.v... y l lnh gi cui cng m dch v nhn c.</dd>
</dl>

<p>Nu mt thnh phn bt u dch v bng cch gi {@link
android.content.Context#startService startService()} (kt qu l mt lnh gi ti {@link
android.app.Service#onStartCommand onStartCommand()}), khi  dch v
s vn chy ti khi t n dng bng {@link android.app.Service#stopSelf()} hoc mt
thnh phn khc dng n bng cch gi {@link android.content.Context#stopService stopService()}.</p>

<p>Nu mt thnh phn gi
{@link android.content.Context#bindService bindService()}  to dch v (v {@link
android.app.Service#onStartCommand onStartCommand()} <em>khng</em> c gi), khi  dch v s ch chy
khi no m thnh phn  cn gn kt vi n. Sau khi dch v c b gn kt khi tt c my khch, h thng
s hy n.</p>

<p>H thng Android s buc dng mt dch v ch khi b nh thp v n phi khi phc ti nguyn
ca h thng cho hot ng c tiu im ca ngi dng. Nu dch v gn kt vi mt hot ng m c tiu im
ca ngi dng, khi  s c t kh nng n s b tt b hn, v nu dch v c khai bo l <a href="#Foreground">chy trong tin cnh</a> ( cp sau), khi  n s hu nh khng bao gi b tt b.
Mt khc, nu dch v c bt u v chy trong thi gian di, h thng s h thp v tr ca n
trong danh sch tc v chy ngm qua thi gian v dch v s rt c th b
tt b&mdash;nu dch v ca bn c bt u, khi  bn phi thit k n 
x l vic khi ng li do h thng mt cch uyn chuyn. Nu h thng tt b dch v ca bn, n s khi ng li dch v ngay khi ti nguyn
c sn tr li (mc d iu ny cng ph thuc vo gi tr m bn tr v t {@link
android.app.Service#onStartCommand onStartCommand()}, vn  ny s c bn sau).  bit thm thng tin
v thi im m h thng c th hy mt dch v, hy xem ti liu <a href="{@docRoot}guide/components/processes-and-threads.html">Tin trnh v Lung</a>
.</p>

<p>Trong nhng phn sau, bn s thy cch bn c th to tng loi dch v v cch s dng
n t cc thnh phn ng dng khc.</p>



<h3 id="Declaring">Khai bo mt dch v trong bn k khai</h3>

<p>Ging nh hot ng (v cc thnh phn khc), bn phi khai bo tt c dch v trong tp bn k khai
ca ng dng ca mnh.</p>

<p> khai bo dch v ca bn, hy thm mt phn t <a href="{@docRoot}guide/topics/manifest/service-element.html">{@code &lt;service&gt;}</a> lm
con ca phn t <a href="{@docRoot}guide/topics/manifest/application-element.html">{@code &lt;application&gt;}</a>
. V d:</p>

<pre>
&lt;manifest ... &gt;
  ...
  &lt;application ... &gt;
      &lt;service android:name=".ExampleService" /&gt;
      ...
  &lt;/application&gt;
&lt;/manifest&gt;
</pre>

<p>Xem tham chiu phn t <a href="{@docRoot}guide/topics/manifest/service-element.html">{@code &lt;service&gt;}</a> 
 bit thm thng tin v vic khai bo dch v ca bn trong bn k khai.</p>

<p>C cc thuc tnh khc m bn c th bao gm trong phn t <a href="{@docRoot}guide/topics/manifest/service-element.html">{@code &lt;service&gt;}</a> 
nh ngha cc tnh cht chng hn nh nhng quyn cn  bt u dch v v tin trnh m
dch v s chy trong . Thuc tnh <a href="{@docRoot}guide/topics/manifest/service-element.html#nm">{@code android:name}</a>
l thuc tnh bt buc duy nht&mdash;n quy nh tn lp ca dch v. Mt khi
bn pht hnh ng dng ca mnh, bn khng nn thay i tn ny, v nu bn lm vy, bn s gp ri ro lm gy
m do s ph thuc vo cc  nh biu th  bt u hoc gn kt dch v (c bi ng blog, <a href="http://android-developers.blogspot.com/2011/06/things-that-cannot-change.html">Nhng iu
Khng Thay i c</a>).

<p> m bo ng dng ca bn c bo mt, <strong>lun s dng mt  nh biu th khi bt u hoc gn kt
{@link android.app.Service}</strong> ca bn v khng c khai bo b lc  nh cho dch v. Nu
iu trng yu l bn phi cho php mt cht khng r rng v dch v no s bt u, bn c th
cung cp b lc  nh cho dch v ca mnh v loi b tn thnh phn khi {@link
android.content.Intent}, nhng sau  bn c th t gi cho  nh bng {@link
android.content.Intent#setPackage setPackage()}, iu ny cung cp s khng r rng va  cho
dch v mc tiu .</p>

<p>Ngoi ra, bn c th m bo rng dch v ca mnh ch sn c cho ng dng ca bn bng cch
a vo thuc tnh <a href="{@docRoot}guide/topics/manifest/service-element.html#exported">{@code android:exported}</a>
v t n thnh {@code "false"}. iu ny s dng vic cc ng dng khc bt u
dch v ca bn, ngay c khi s dng mt  nh biu th.</p>




<h2 id="CreatingStartedService">To mt Dch v c Bt u</h2>

<p>Dch v c bt u l dch v m mt thnh phn khc bt u bng cch gi {@link
android.content.Context#startService startService()}, kt qu l mt lnh gi ti phng php
{@link android.app.Service#onStartCommand onStartCommand()} ca dch v.</p>

<p>Khi mt dch v c bt u, n c mt vng i c lp vi
thnh phn  bt u n v dch v c th chy ngm v thi hn, ngay c khi
thnh phn bt u n b hy. Nh vy, dch v s t dng khi lm xong cng vic ca n
bng cch gi {@link android.app.Service#stopSelf stopSelf()}, hoc mt thnh phn khc c th dng n
bng cch gi {@link android.content.Context#stopService stopService()}.</p>

<p>Mt thnh phn ng dng chng hn nh mt hot ng c th bt u dch v bng cch gi {@link
android.content.Context#startService startService()} v chuyn mt {@link android.content.Intent}
trong  quy nh dch v v bao gm bt k d liu no  cho dch v s dng. Dch v s nhn
{@link android.content.Intent} ny trong phng php {@link android.app.Service#onStartCommand
onStartCommand()}.</p>

<p>V d, gi s mt hot ng cn lu mt s d liu vo c s d liu trc tuyn. Hot ng c th
bt u mt dch v ng hnh v truyn cho n d liu  lu bng cch chuyn mt  nh ti {@link
android.content.Context#startService startService()}. Dch v s nhn  nh trong {@link
android.app.Service#onStartCommand onStartCommand()}, kt ni vi Internet v thc hin
giao tc c s d liu. Khi giao tc c thc hin, dch v s t dng li v n b
hy.</p>

<p class="caution"><strong>Ch :</strong> Mt dch v s chy trong cng tin trnh nh ng dng
m n c khai bo trong  v trong lung chnh ca ng dng  theo mc nh. V vy, nu dch v ca bn
thc hin cc thao tc tng cng hoc chn trong khi ngi dng tng tc vi mt hot ng t cng
ng dng, dch v s lm chm hiu nng ca hot ng.  trnh tc ng ti hiu nng ca
ng dng, bn nn bt u mt lung mi bn trong dch v.</p>

<p>Thng thng, c hai lp m bn c th m rng  to mt dch v c bt u:</p>
<dl>
  <dt>{@link android.app.Service}</dt>
  <dd>y l lp c bn cho tt c dch v. Khi bn m rng lp ny, iu quan trng l
bn to mt lung mi  thc hin tt c cng vic ca dch v trong , do dch v s dng lung chnh
ca ng dng ca bn, theo mc nh, iu ny c th lm chm hiu nng ca bt k hot ng no m ng dng
ca bn ang chy.</dd>
  <dt>{@link android.app.IntentService}</dt>
  <dd>y l mt lp con ca {@link android.app.Service} c chc nng s dng mt lung trnh thc hin  x l tt c
yu cu bt u mt cch ln lt. y l la chn tt nht nu bn khng yu cu dch v ca mnh
x l ng thi nhiu yu cu. Tt c nhng g bn cn lm  l trin khai {@link
android.app.IntentService#onHandleIntent onHandleIntent()}, n s nhn  nh cho mi
yu cu bt u  bn c th thc hin cng vic chy ngm.</dd>
</dl>

<p>Cc phn sau m t cch bn c th trin khai dch v ca mnh bng cch s dng mt trong cc cch cho nhng lp
ny.</p>


<h3 id="ExtendingIntentService">M rng lp IntentService</h3>

<p>V phn ln cc dch v c bt u khng cn x l nhiu yu cu mt cch ng thi
(iu ny thc s c th l mt kch bn to a lung nguy him), c l tt nht l nu bn
trin khai dch v ca mnh bng cch s dng lp {@link android.app.IntentService}.</p>

<p>{@link android.app.IntentService} lm iu sau y:</p>

<ul>
  <li>To mt lung trnh thc hin mc nh  thc thi tt c  nh c chuyn ti {@link
android.app.Service#onStartCommand onStartCommand()} tch ring vi lung
chnh ca ng dng ca bn.</li>
  <li>To mt hng i cng vic  chuyn ln lt tng  nh ti trin khai {@link
android.app.IntentService#onHandleIntent onHandleIntent()} ca bn, v th bn khng bao gi phi
lo lng v vn  to a lung.</li>
  <li>Dng dch v sau khi tt c yu cu bt u u  c x l, v th bn khng bao gi phi gi
{@link android.app.Service#stopSelf}.</li>
  <li>Cung cp trin khai mc nh ca {@link android.app.IntentService#onBind onBind()} m
tr v rng.</li>
  <li>Cung cp trin khai mc nh ca {@link android.app.IntentService#onStartCommand
onStartCommand()} m gi  nh ti hng i cng vic ri ti trin khai {@link
android.app.IntentService#onHandleIntent onHandleIntent()} ca bn.</li>
</ul>

<p>Tt c u ni ln mt thc t rng tt c nhng vic bn cn lm  l trin khai {@link
android.app.IntentService#onHandleIntent onHandleIntent()}  thc hin cng vic m
my khch cung cp. (Mc d bn cng cn cung cp mt hm dng nh cho dch v.)</p>

<p>Sau y l v d v trin khai {@link android.app.IntentService}:</p>

<pre>
public class HelloIntentService extends IntentService {

  /**
   * A constructor is required, and must call the super {@link android.app.IntentService#IntentService}
   * constructor with a name for the worker thread.
   */
  public HelloIntentService() {
      super("HelloIntentService");
  }

  /**
   * The IntentService calls this method from the default worker thread with
   * the intent that started the service. When this method returns, IntentService
   * stops the service, as appropriate.
   */
  &#64;Override
  protected void onHandleIntent(Intent intent) {
      // Normally we would do some work here, like download a file.
      // For our sample, we just sleep for 5 seconds.
      long endTime = System.currentTimeMillis() + 5*1000;
      while (System.currentTimeMillis() &lt; endTime) {
          synchronized (this) {
              try {
                  wait(endTime - System.currentTimeMillis());
              } catch (Exception e) {
              }
          }
      }
  }
}
</pre>

<p> l tt c nhng g bn cn: mt hm dng v trin khai {@link
android.app.IntentService#onHandleIntent onHandleIntent()}.</p>

<p>Nu bn quyt nh cng khng ch cc phng php gi li khc, chng hn nh {@link
android.app.IntentService#onCreate onCreate()}, {@link
android.app.IntentService#onStartCommand onStartCommand()}, hoc {@link
android.app.IntentService#onDestroy onDestroy()}, hy nh gi ra siu trin khai, sao
cho {@link android.app.IntentService} c th x l hp l vng i ca lung trnh thc hin.</p>

<p>V d, {@link android.app.IntentService#onStartCommand onStartCommand()} phi tr v
trin khai mc nh ( l cch m  nh c chuyn ti {@link
android.app.IntentService#onHandleIntent onHandleIntent()}):</p>

<pre>
&#64;Override
public int onStartCommand(Intent intent, int flags, int startId) {
    Toast.makeText(this, "service starting", Toast.LENGTH_SHORT).show();
    return super.onStartCommand(intent,flags,startId);
}
</pre>

<p>Bn cnh {@link android.app.IntentService#onHandleIntent onHandleIntent()}, phng php duy nht m
t  bn khng cn gi siu lp l {@link android.app.IntentService#onBind
onBind()} (nhng bn ch cn trin khai iu  nu dch v ca bn cho php gn kt).</p>

<p>Trong phn tip theo, bn s thy cch m cng loi dch v c trin khai khi m rng
lp {@link android.app.Service} c s, n c nhiu m hn nhng c th
ph hp nu bn cn x l cc yu cu bt u ng thi.</p>


<h3 id="ExtendingService">M rng lp Dch v</h3>

<p>Nh bn thy trong phn trc, s dng {@link android.app.IntentService} gip vic
trin khai mt dch v c bt u ca bn tr nn rt n gin. Tuy nhin, nu bn cn dch v ca mnh
thc hin to a lung (thay v x l cc yu cu bt u thng qua mt hng i cng vic), khi  bn
c th m rng lp {@link android.app.Service}  x l tng  nh.</p>

<p> so snh, on m mu sau l trin khai lp {@link
android.app.Service} m thc hin chnh xc cng cng vic nh v d bn trn bng cch s dng {@link
android.app.IntentService}. C th, i vi mi yu cu bt u, n s s dng mt lung trnh thc hin  thc hin
cng vic v ch x l ln lt tng yu cu mt.</p>

<pre>
public class HelloService extends Service {
  private Looper mServiceLooper;
  private ServiceHandler mServiceHandler;

  // Handler that receives messages from the thread
  private final class ServiceHandler extends Handler {
      public ServiceHandler(Looper looper) {
          super(looper);
      }
      &#64;Override
      public void handleMessage(Message msg) {
          // Normally we would do some work here, like download a file.
          // For our sample, we just sleep for 5 seconds.
          long endTime = System.currentTimeMillis() + 5*1000;
          while (System.currentTimeMillis() &lt; endTime) {
              synchronized (this) {
                  try {
                      wait(endTime - System.currentTimeMillis());
                  } catch (Exception e) {
                  }
              }
          }
          // Stop the service using the startId, so that we don't stop
          // the service in the middle of handling another job
          stopSelf(msg.arg1);
      }
  }

  &#64;Override
  public void onCreate() {
    // Start up the thread running the service.  Note that we create a
    // separate thread because the service normally runs in the process's
    // main thread, which we don't want to block.  We also make it
    // background priority so CPU-intensive work will not disrupt our UI.
    HandlerThread thread = new HandlerThread("ServiceStartArguments",
            Process.THREAD_PRIORITY_BACKGROUND);
    thread.start();

    // Get the HandlerThread's Looper and use it for our Handler
    mServiceLooper = thread.getLooper();
    mServiceHandler = new ServiceHandler(mServiceLooper);
  }

  &#64;Override
  public int onStartCommand(Intent intent, int flags, int startId) {
      Toast.makeText(this, "service starting", Toast.LENGTH_SHORT).show();

      // For each start request, send a message to start a job and deliver the
      // start ID so we know which request we're stopping when we finish the job
      Message msg = mServiceHandler.obtainMessage();
      msg.arg1 = startId;
      mServiceHandler.sendMessage(msg);

      // If we get killed, after returning from here, restart
      return START_STICKY;
  }

  &#64;Override
  public IBinder onBind(Intent intent) {
      // We don't provide binding, so return null
      return null;
  }

  &#64;Override
  public void onDestroy() {
    Toast.makeText(this, "service done", Toast.LENGTH_SHORT).show();
  }
}
</pre>

<p>Nh bn c th thy, c nhiu vic hn nhiu so vi vic s dng {@link android.app.IntentService}.</p>

<p>Tuy nhin, do bn t mnh x l tng lnh gi n {@link android.app.Service#onStartCommand
onStartCommand()}, bn c th thc hin nhiu yu cu mt cch ng thi.  khng phi l vic
m v d ny lm, nhng nu  l vic bn mun, vy bn c th to mt lung mi cho tng
yu cu v ngay lp tc tr chng v (thay v i ti khi yu cu trc hon thnh).</p>

<p>  rng phng php {@link android.app.Service#onStartCommand onStartCommand()} phi tr v mt
s nguyn. S nguyn l mt gi tr m t cch h thng nn tip tc dch v trong
trng hp h thng tt b n (nh c  cp  trn, trin khai mc nh cho {@link
android.app.IntentService} s x l iu ny cho bn d bn c th sa i n). Gi tr tr v
t {@link android.app.Service#onStartCommand onStartCommand()} phi l mt trong cc
hng s sau:</p>

<dl>
  <dt>{@link android.app.Service#START_NOT_STICKY}</dt>
    <dd>Nu h thng tt b dch v sau khi {@link android.app.Service#onStartCommand
onStartCommand()} tr v, <em>khng</em> c to li dch v , tr khi c cc  nh
ang ch  c chuyn. y l la chn an ton nht  trnh chy dch v ca bn khi khng cn thit
v khi ng dng ca bn c th n thun khi ng li bt k cng vic cha hon thnh no.</dd>
  <dt>{@link android.app.Service#START_STICKY}</dt>
    <dd>Nu h thng tt b dch v sau khi {@link android.app.Service#onStartCommand
onStartCommand()} tr v, hy to li dch v v gi {@link
android.app.Service#onStartCommand onStartCommand()}, nhng <em>khng</em> chuyn li  nh cui cng.
Thay vo , h thng s gi {@link android.app.Service#onStartCommand onStartCommand()} bng mt
 nh rng, tr khi c cc  nh ang ch  bt u dch v, trong trng hp ,
nhng  nh ny s c chuyn. iu ny ph hp vi cc trnh pht phng tin (hoc dch v tng t) m khng
ang thc thi lnh, nhng ang chy v thi hn v ch mt tc v.</dd>
  <dt>{@link android.app.Service#START_REDELIVER_INTENT}</dt>
    <dd>Nu h thng tt b dch v sau khi {@link android.app.Service#onStartCommand
onStartCommand()} tr v, hy to li dch v v gi {@link
android.app.Service#onStartCommand onStartCommand()} bng  nh cui cng c chuyn ti
dch v. Mi  nh ch u c chuyn ln lt. iu ny ph hp vi cc dch v ang
ch ng thc hin mt cng vic m nn c tip tc ngay lp tc, chng hn nh ti xung mt tp.</dd>
</dl>
<p> bit thm chi tit v nhng gi tr tr v ny, hy xem ti liu tham kho c lin kt cho tng
hng s.</p>



<h3 id="StartingAService">Bt u mt Dch v</h3>

<p>Bn c th bt u mt dch v t mt hot ng hoc thnh phn ng dng khc bng cch chuyn mt
{@link android.content.Intent} (quy nh dch v s bt u) n {@link
android.content.Context#startService startService()}. H thng Android s gi phng php {@link
android.app.Service#onStartCommand onStartCommand()} ca dch v v chuyn cho n {@link
android.content.Intent}. (Bn tuyt i khng nn trc tip gi {@link android.app.Service#onStartCommand
onStartCommand()}.)</p>

<p>V d, mt hot ng c th bt u dch v v d trong phn trc ({@code
HelloSevice}) bng cch s dng mt  nh biu th vi {@link android.content.Context#startService
startService()}:</p>

<pre>
Intent intent = new Intent(this, HelloService.class);
startService(intent);
</pre>

<p>Phng php {@link android.content.Context#startService startService()} ngay lp tc tr v v
h thng Android s gi phng php {@link android.app.Service#onStartCommand
onStartCommand()} ca dch v. Nu dch v khng ang chy, trc tin h thng s gi {@link
android.app.Service#onCreate onCreate()}, ri gi {@link android.app.Service#onStartCommand
onStartCommand()}.</p>

<p>Nu dch v cng khng cung cp kh nng gn kt,  nh c chuyn bng {@link
android.content.Context#startService startService()} s l phng thc giao tip duy nht gia
thnh phn ng dng v dch v. Tuy nhin, nu bn mun dch v gi mt kt qu tr li, khi 
my khch m bt u dch v c th to mt {@link android.app.PendingIntent} cho mt qung b
(bng {@link android.app.PendingIntent#getBroadcast getBroadcast()}) v chuyn n ti dch v
trong {@link android.content.Intent} m bt u dch v. Khi , dch v c th s dng
qung b  chuyn kt qu.</p>

<p>Nhiu yu cu bt u dch v s dn n nhiu lnh gi tng ng ti
{@link android.app.Service#onStartCommand onStartCommand()} ca dch v. Tuy nhin, ch c mt yu cu dng
dch v (bng {@link android.app.Service#stopSelf stopSelf()} hoc {@link
android.content.Context#stopService stopService()}) l bt buc  dng n.</p>


<h3 id="Stopping">Dng mt dch v</h3>

<p>Dch v c bt u phi qun l vng i ca chnh n. C th, h thng khng dng
hay hy dch v tr khi n phi khi phc b nh ca h thng v dch v
s tip tc chy sau khi {@link android.app.Service#onStartCommand onStartCommand()} tr v. V vy,
dch v phi t dng bng cch gi {@link android.app.Service#stopSelf stopSelf()} hoc mt thnh phn
khc c th dng n bng cch gi {@link android.content.Context#stopService stopService()}.</p>

<p>Sau khi c yu cu dng bng {@link android.app.Service#stopSelf stopSelf()} hoc {@link
android.content.Context#stopService stopService()}, h thng s hy dch v ngay khi
c th.</p>

<p>Tuy nhin, nu dch v ca bn x l nhiu yu cu {@link
android.app.Service#onStartCommand onStartCommand()} ng thi, khi  bn khng nn dng
dch v khi bn  hon thnh x l yu cu bt u, v bn c th  nhn c mt
yu cu bt u mi k t thi im  (dng khi kt thc yu cu th nht s chm dt yu cu th hai).  trnh
vn  ny, bn c th s dng {@link android.app.Service#stopSelf(int)}  m bo rng yu cu
dng dch v ca bn lun c da trn yu cu bt u gn y nht. C th, khi bn gi {@link
android.app.Service#stopSelf(int)}, bn s chuyn ID ca yu cu bt u (<code>startId</code>
c chuyn ti {@link android.app.Service#onStartCommand onStartCommand()}) m yu cu dng ca bn
tng ng vi. Khi , nu dch v  nhn c mt yu cu bt u mi trc khi bn c th gi {@link
android.app.Service#stopSelf(int)}, vy ID s khng khp v dch v s khng dng.</p>

<p class="caution"><strong>Ch :</strong> iu quan trng l ng dng ca bn dng dch v ca n
khi n hon thnh xong cng vic  trnh lng ph ti nguyn ca h thng v tn pin. Nu cn,
cc thnh phn khc c th dng dch v bng cch gi {@link
android.content.Context#stopService stopService()}. Ngay c khi bn kch hot gn kt cho dch v,
bn phi lun t mnh dng dch v nu dch v  nhn c lnh gi ti {@link
android.app.Service#onStartCommand onStartCommand()}.</p>

<p> bit thm thng tin v vng i ca mt dch v, hy xem phn bn di v <a href="#Lifecycle">Qun l Vng i ca mt Dch v</a>.</p>



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

<p>Dch v gn kt l mt dch v cho php cc thnh phn ng dng gn kt vi n bng cch gi {@link
android.content.Context#bindService bindService()}  to mt kt ni lu di
(v thng khng cho php cc thnh phn <em>bt u</em> n bng cch gi {@link
android.content.Context#startService startService()}).</p>

<p>Bn nn to mt dch v gn kt khi mun tng tc vi dch v t hot ng
v cc thnh phn khc trong ng dng ca mnh hoc  hin th mt s tnh nng trong ng dng ca bn cho
cc ng dng khc thng qua truyn thng lin tin trnh (IPC).</p>

<p> to mt dch v gn kt, bn phi trin khai phng php gi li {@link
android.app.Service#onBind onBind()}  tr v mt {@link android.os.IBinder} m
nh ngha giao din cho giao tip vi dch v . Khi , cc thnh phn ng dng khc c th gi
{@link android.content.Context#bindService bindService()}  truy xut giao din v
bt u cc phng php gi trn dch v. Dch v tn ti ch nhm phc v thnh phn ng dng m
c gn kt vi n, v th khi khng c thnh phn c gn kt vi dch v, h thng s hy n
(bn <em>khng</em> cn dng mt dch v gn kt theo cch phi lm khi dch v c bt u
thng qua {@link android.app.Service#onStartCommand onStartCommand()}).</p>

<p> to mt dch v gn kt, iu u tin bn phi lm l nh ngha giao din quy nh
cch thc m mt my khch c th giao tip vi dch v. Giao din gia dch v v
my khch ny phi l mt trin khai {@link android.os.IBinder} v c dch v ca bn phi
tr v t phng php gi li {@link android.app.Service#onBind
onBind()}. Sau khi my khch nhn c {@link android.os.IBinder}, n c th bt u
tng tc vi dch v thng qua giao din .</p>

<p>Nhiu my khch c th gn kt vi dch v ng thi. Khi mt my khch hon thnh tng tc vi
dch v, n s gi {@link android.content.Context#unbindService unbindService()}  b gn kt. Sau khi
khng cn my khch no c gn kt vi dch v, h thng s hy dch v.</p>

<p>C nhiu cch  trin khai mt dch v gn kt v trin khai s phc tp
hn so vi dch v c bt u, v th ni dung bn v dch v gn kt c trnh by trong mt
ti liu ring v <a href="{@docRoot}guide/components/bound-services.html">Dch v Gn kt</a>.</p>



<h2 id="Notifications">Gi Thng bo ti Ngi dng</h2>

<p>Sau khi chy, mt dch v c th thng bo cho ngi dng v s kin bng cch s dng <a href="{@docRoot}guide/topics/ui/notifiers/toasts.html">Thng bo Ca s</a> hoc <a href="{@docRoot}guide/topics/ui/notifiers/notifications.html">Thng bo Thanh Trng thi</a>.</p>

<p>Thng bo ca s l mt thng bo xut hin mt lc trn b mt ca ca s hin ti 
ri bin mt, trong khi thng bo thanh trng thi cung cp mt biu tng trong thanh trng thi cng mt
thng bo, ngi dng c th chn n  thc hin mt hnh ng (chng hn nh bt u mt hot ng).</p>

<p>Thng thng thng bo thanh trng thi l k thut tt nht khi mt cng vic nn no   hon thnh
(chng hn nh mt tp  hon thnh
vic ti xung) v lc ny ngi dng c th hnh ng da trn n. Khi ngi dng chn thng bo t dng xem m rng
, thng bo c th bt u mt hot ng (chng hn nh xem tp c ti xung).</p>

<p>Xem hng dn dnh cho nh pht trin <a href="{@docRoot}guide/topics/ui/notifiers/toasts.html">Thng bo Ca s</a> hoc <a href="{@docRoot}guide/topics/ui/notifiers/notifications.html">Thng bo Thanh Trng thi</a>
 bit thm thng tin.</p>



<h2 id="Foreground">Chy mt Dch v trong Tin cnh</h2>

<p>Dch v tin cnh l mt dch v c coi l iu m
ngi dng ang ch ng quan tm, v th n khng c  ngh  h thng tt b khi b nh thp. Dch v
tin cnh phi cung cp mt thng bo cho thanh trng thi, n c t di tiu 
"ang din ra", iu ny c ngha l thng bo khng th loi b c tr khi dch v
b dng hoc loi b khi tin cnh.</p>

<p>V d, mt trnh chi nhc ang pht nhc t mt dch v nn c t  chy trong
tin cnh, v ngi dng r rng  thc c
hot ng ca n. Thng bo trong thanh trng thi c th cho bit bi ht ang chi v cho php
ngi dng khi chy mt hot ng  tng tc vi trnh chi nhc.</p>

<p> yu cu dch v ca bn chy trong tin cnh, hy gi {@link
android.app.Service#startForeground startForeground()}. Phng php ny dng hai tham s: mt s nguyn
 xc nh duy nht thng bo v {@link
android.app.Notification} cho thanh trng thi. V d:</p>

<pre>
Notification notification = new Notification(R.drawable.icon, getText(R.string.ticker_text),
        System.currentTimeMillis());
Intent notificationIntent = new Intent(this, ExampleActivity.class);
PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, notificationIntent, 0);
notification.setLatestEventInfo(this, getText(R.string.notification_title),
        getText(R.string.notification_message), pendingIntent);
startForeground(ONGOING_NOTIFICATION_ID, notification);
</pre>

<p class="caution"><strong>Ch :</strong> ID s nguyn m bn cp cho {@link
android.app.Service#startForeground startForeground()} khng c bng 0.</p>


<p> xa b dch v khi tin cnh, hy gi {@link
android.app.Service#stopForeground stopForeground()}. Phng php ny dng mt boolean, cho bit
c loi b c thng bo thanh trng thi hay khng. Phng php ny <em>khng</em> dng
dch v. Tuy nhin, nu bn dng dch v trong khi n vn ang chy trong tin cnh, khi  thng bo
cng b loi b.</p>

<p> bit thm thng tin v thng bo, hy xem phn <a href="{@docRoot}guide/topics/ui/notifiers/notifications.html">To Thng bo
Thanh Trng thi</a>.</p>



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

<p>Vng i ca mt dch v n gin hn nhiu so vi vng i ca mt hot ng. Tuy nhin, mt iu thm ch cn quan trng hn
 l bn phi tht ch  ti cch dch v ca bn c to v hy, bi mt dch v
c th chy ngm m ngi dng khng bit.</p>

<p>Vng i ca dch v&mdash;t khi n c to ti khi n b hy&mdash;c th i theo hai
con ng khc nhau:</p>

<ul>
<li>Dch v c bt u
  <p>Dch v c to khi mt thnh phn khc gi {@link
android.content.Context#startService startService()}. Sau , dch v s chy v thi hn v phi
t dng bng cch gi {@link
android.app.Service#stopSelf() stopSelf()}. Mt thnh phn khc cng c th dng
dch v bng cch gi {@link android.content.Context#stopService
stopService()}. Khi dch v b dng, h thng s hy n.</p></li>

<li>Dch v gn kt
  <p>Dch v c to khi mt thnh phn khc (my khch) gi {@link
android.content.Context#bindService bindService()}. Khi , my khch giao tip vi dch v
thng qua mt giao din {@link android.os.IBinder}. My khch c th ng kt ni bng cch gi
{@link android.content.Context#unbindService unbindService()}. Nhiu my khch c th gn kt vi
cng dch v v khi tt c chng b gn kt, h thng s hy dch v. (Dch v
<em>khng</em> cn t mnh dng.)</p></li>
</ul>

<p>Hai con ng ny hon ton ring bit. C th, bn c th gn kt vi mt dch v 
c bt u bng {@link android.content.Context#startService startService()}. V d, mt dch v
nhc nn c th c bt u bng cch gi {@link android.content.Context#startService
startService()} bng mt {@link android.content.Intent} m s nhn bit nhc  pht. Sau ,
c th l khi ngi dng mun thc thi mt quyn iu khin i vi trnh pht  hoc ly thng tin v
bi ht ang pht, hot ng c th gn kt vi dch v bng cch gi {@link
android.content.Context#bindService bindService()}. Trong nhng trng hp nh vy, {@link
android.content.Context#stopService stopService()} hoc {@link android.app.Service#stopSelf
stopSelf()} khng thc s dng dch v ti khi tt c my khch b gn kt. </p>


<h3 id="LifecycleCallbacks">Trin khai gi li vng i</h3>

<p>Ging nh mt hot ng, dch v c cc phng php gi li vng i m bn c th trin khai  theo di
nhng thay i v trng thi ca dch v v thc hin cng vic ti nhng thi im ph hp. Dch v khung sau
minh ha tng phng php vng i:</p>

<pre>
public class ExampleService extends Service {
    int mStartMode;       // indicates how to behave if the service is killed
    IBinder mBinder;      // interface for clients that bind
    boolean mAllowRebind; // indicates whether onRebind should be used

    &#64;Override
    public void {@link android.app.Service#onCreate onCreate}() {
        // The service is being created
    }
    &#64;Override
    public int {@link android.app.Service#onStartCommand onStartCommand}(Intent intent, int flags, int startId) {
        // The service is starting, due to a call to {@link android.content.Context#startService startService()}
        return <em>mStartMode</em>;
    }
    &#64;Override
    public IBinder {@link android.app.Service#onBind onBind}(Intent intent) {
        // A client is binding to the service with {@link android.content.Context#bindService bindService()}
        return <em>mBinder</em>;
    }
    &#64;Override
    public boolean {@link android.app.Service#onUnbind onUnbind}(Intent intent) {
        // All clients have unbound with {@link android.content.Context#unbindService unbindService()}
        return <em>mAllowRebind</em>;
    }
    &#64;Override
    public void {@link android.app.Service#onRebind onRebind}(Intent intent) {
        // A client is binding to the service with {@link android.content.Context#bindService bindService()},
        // after onUnbind() has already been called
    }
    &#64;Override
    public void {@link android.app.Service#onDestroy onDestroy}() {
        // The service is no longer used and is being destroyed
    }
}
</pre>

<p class="note"><strong>Lu :</strong> Khng nh cc phng php gi li vng i ca hot ng, bn
<em>khng</em> phi gi trin khai siu lp vi nhng phng php gi li ny.</p>

<img src="{@docRoot}images/service_lifecycle.png" alt="" />
<p class="img-caption"><strong>Hnh 2.</strong> Vng i dch v. S  pha bn tri
minh ha vng i khi dch v c to bng {@link android.content.Context#startService
startService()} v s  pha bn phi minh ha vng i khi dch v c to
bng {@link android.content.Context#bindService bindService()}.</p>

<p>Bng vic trin khai nhng phng php ny, bn c th theo di hai vng lp lng nhau trong vng i ca dch v: </p>

<ul>
<li><strong>Ton b vng i</strong> ca mt dch v xy ra gia thi im gi {@link
android.app.Service#onCreate onCreate()} v thi im {@link
android.app.Service#onDestroy} tr v. Ging nh hot ng, dch v thc hin thit lp ban u ca n trong
{@link android.app.Service#onCreate onCreate()} v gii phng tt c ti nguyn cn li trong {@link
android.app.Service#onDestroy onDestroy()}.  V d, mt
dch v pht li nhc c th to lung m ti  nhc s c pht trong {@link
android.app.Service#onCreate onCreate()}, sau  dng lung trong {@link
android.app.Service#onDestroy onDestroy()}.

<p>Cc phng php {@link android.app.Service#onCreate onCreate()} v {@link android.app.Service#onDestroy
onDestroy()} c gi cho tt c dch v, d
chng c to bi {@link android.content.Context#startService startService()} hay {@link
android.content.Context#bindService bindService()}.</p></li>

<li><strong>Vng i hin hot</strong> ca mt dch v s bt u bng mt lnh gi n hoc {@link
android.app.Service#onStartCommand onStartCommand()} hoc {@link android.app.Service#onBind onBind()}.
Mi phng php s c giao {@link
android.content.Intent} m c chuyn tng ng cho hoc {@link android.content.Context#startService
startService()} hoc {@link android.content.Context#bindService bindService()}.
<p>Nu dch v c bt u, vng i hin hot s chm dt ti cng thi im khi ton b vng i
chm dt (dch v s vn hin hot ngay c sau khi {@link android.app.Service#onStartCommand
onStartCommand()} tr v). Nu dch v b gn kt, vng i hin hot s chm dt khi {@link
android.app.Service#onUnbind onUnbind()} tr v.</p>
</li>
</ul>

<p class="note"><strong>Lu :</strong> Mc d dch v c bt u b dng bi mt lnh gi n
hoc {@link android.app.Service#stopSelf stopSelf()} hoc {@link
android.content.Context#stopService stopService()}, s khng c mt lnh gi li tng ng cho
dch v (khng c lnh gi li {@code onStop()}). V th, tr khi dch v c gn kt vi mt my khch,
h thng s hy n khi dch v b dng&mdash;{@link
android.app.Service#onDestroy onDestroy()} l lnh gi li duy nht nhn c.</p>

<p>Hnh 2 minh ha cc phng php gi li in hnh cho mt dch v. Mc d hnh tch ring
cc dch v c to bi {@link android.content.Context#startService startService()} vi cc dch v
c to bi {@link android.content.Context#bindService bindService()}, hy
ghi nh rng bt k dch v no, d c bt u nh th no, u c th cho php my khch gn kt vi n.
V th, mt dch v c bt u t u bng {@link android.app.Service#onStartCommand
onStartCommand()} (bi mt my khch gi {@link android.content.Context#startService startService()})
vn c th nhn mt lnh gi n {@link android.app.Service#onBind onBind()} (khi my khch gi
{@link android.content.Context#bindService bindService()}).</p>

<p> bit thm thng tin v vic tao mt dch v c tnh nng gn kt, hy xem ti liu <a href="{@docRoot}guide/components/bound-services.html">Dch v Gn kt</a>,
trong  c thm thng tin v phng php gi li {@link android.app.Service#onRebind onRebind()}
trong phn v <a href="{@docRoot}guide/components/bound-services.html#Lifecycle">Qun l Vng i ca
mt Dch v Gn kt</a>.</p>


<!--
<h2>Beginner's Path</h2>

<p>To learn how to query data from the system or other applications (such as contacts or media
stored on the device), continue with the <b><a
href="{@docRoot}guide/topics/providers/content-providers.html">Content Providers</a></b>
document.</p>
-->