本文主要講activity如何與service進行互動,這個互動很常見,如在一個音樂播放器中,service負責音樂的播放,activity負責前端UI,當你在前端對進度調節時,需要向servie發出一個指令,而service播放音樂的進度也需要及時的傳回給activity,使得activity的進度條能夠向後滑動。本文所參考的是官網。上面有詳細的例子,這裡不再詳述。 1 service和activity在同一程序時,使用IBinder 當activity需要和service互動時,采用service的第二種啟動方式,即 bindService(),将avtivity(準确的說是clients,因為其他元件也可以和service綁定)和service綁定。一方面,service需要建立自己的IBinder類,繼承Binder,override這個類的onBind()方法,在該方法中向clients傳回這個IBinder執行個體。另一方面,clients需要實作一個ServiceConnection對象(是一個内部匿名類),clients可以利用這個ServiceConnection中的onServiceConnected()方法擷取這個IBinder執行個體,在通過這個IBinder中的方法擷取service的執行個體,進而通路service的public方法。 這種方法非常适合service隻是activity的一個背景工作,再次強調,這種方法隻适于 同一程序的activity和service,在預設情況下的service和activity是在同一個程序中的,除非在manifest中另外聲明 android:process 屬性。 而且在例子中也隻有 activity向service 發送消息,service向activity發送消息還沒有找到,學渣認為可以用廣播。 這裡有一個例子,activity可以通過IBinder調用service中的方法,大家可以參考,首先是service,在service中聲明一個IBinder類的執行個體,在onBind時向clients傳回這個IBinder對象,而clients可以通過onServiceConnected()擷取IBinder執行個體,代碼如下:
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;
}
}
@Override
public IBinder onBind(Intent intent) {
return mBinder;
}
/** method for clients */
public int getRandomNumber() {
return mGenerator.nextInt(100);
}
}
activity的使用:
public class BindingActivity extends Activity {
LocalService mService;
boolean mBound = false;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
@Override
protected void onStart() {
super.onStart();
// Bind to LocalService
Intent intent = new Intent(this, LocalService.class);
bindService(intent, mConnection, Context.BIND_AUTO_CREATE);
}
@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() {
@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;
}
@Override
public void onServiceDisconnected(ComponentName arg0) {
mBound = false;
}
};
}
2 service和activity不在同一程序 (1)使用Messager , 這是最簡單的IPC,在service中定義一個Handler用來處理不同的Message對象
(2)使用AIDL 由于學渣現在還沒有用到這塊,暫時停一下,以後學了會繼續更新本部落格。