綁定型服務是什麼?
綁定型服務是服務的一種，可以綁定應用程式元件並透過已定義的介面和元件互動。元件可以透過該介面呼叫服務的方法。
實作綁定型服務
透過繼承Service類別來建立綁定型服務，需要實作onBind方法，就是最簡單的綁定型服務。
public class BindService extends Service {
public BindService() {
}
@Override
public IBinder onBind(Intent intent) {
// TODO: Return the communication channel to the service.
throw new UnsupportedOperationException("Not yet implemented");
}
}
重點為onBind方法，該方法會在元件綁定服務時執行，參數intent會從元件傳遞進來以攜帶需要從元件傳入的資料。
onBinder方法會回傳IBinder，當IBinder回傳到元件之後，元件便可透過IBinder和服務互動。
實作IBinder
IBinder是一個介面，其用途為讓元件取得服務的參考以進行和服務之間的互動。
因為Android已提供Binder類別，Binder類別已經實作IBinder介面中重要的方法。所以我們不必自己再實作IBinder介面，只需要建立Binder的子類別，並在該子類別中傳回服務的參考即可。
public class BindService extends Service {
private IBinder mBinder = new ServiceBinder();
public BindService() {
}
public class ServiceBinder extends Binder {
public BindService getBindService() {
return BindService.this;
}
}
@Override
public IBinder onBind(Intent intent) {
return mBinder;
}
public int getRandom(){
return new Random().nextInt(100);
}
}
ServiceBinder類別的getBindService方法會回傳服務本身，元件就是透過這個方法取得服務的參考並與其互動。
實作ServiceConnection
當元件和服務進行綁定時是透過呼叫bindService方法來執行，如下
bindService(IntentToService, serviceConnect, Context.BIND_AUTO_CREATE);
該方法第2個參數為ServiceConnect物件，元件透過ServiceConnect物件取得目前和服務綁定的狀況(已連結或已中斷)，我們需要建立ServiceConnect物件並實作2個方法，分別為
@Override
public void onServiceConnected(ComponentName name, IBinder service) {}
onServiceConnected方法會在元件綁定服務時被呼叫，該方法的IBinder參數即為從服務的onBind方法回傳，我們就可以透過該參數來取得服務。
@Override
public void onServiceDisconnected(ComponentName name) {}
onServiceDisconnected方法會在元件和服務中斷時被呼叫。
建立BindServiceActivity如下
public class BindServiceActivity extends AppCompatActivity {
private ServiceConnection mServiceConnection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName name, IBinder binder) {
}
@Override
public void onServiceDisconnected(ComponentName name) {
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_bind_service);
}
}
接著在ServiceConnection的onServiceConnected方法中實作透過傳入的binder取得服務的參考。
private BindService mBindService;
private ServiceConnection mServiceConnection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName name, IBinder binder) {
ServiceBinder serviceBinder = (ServiceBinder) binder;
mBindService = serviceBinder.getBindService();
}
@Override
public void onServiceDisconnected(ComponentName name) {
}
};
另外在元件中還需要一個布林變數來記錄目前是否已綁定服務，這個變數主要是方便元件對服務進行綁定或解綁定。
private boolean mIsServiceBound;
private ServiceConnection mServiceConnection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName name, IBinder binder) {
ServiceBinder serviceBinder = (ServiceBinder) binder;
mBindService = serviceBinder.getBindService();
mIsServiceBound = true;
}
@Override
public void onServiceDisconnected(ComponentName name) {
mIsServiceBound = false;
}
};
綁定服務或解綁定服務
以Activity來說綁定服務的實作位置通常會在onCreate或onStart，而解綁定的位置會對應綁定的位置。
若Activity移到後台時也要持續從服務收到更新，那就在onCreate綁定然後在onDestroy解綁定。
若Activity只有在前台顯示時需要收到服務的更新，在後台時不需要。就在onStart綁定然後在onStop解綁定。
以下在onCreate綁定服務，在onDestroy解綁定服務。
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_bind_service);
Intent bindService = new Intent(this, BindService.class);
if (!mIsServiceBound) {
bindService(bindService, mServiceConnection, Context.BIND_AUTO_CREATE);
}
}
@Override
protected void onDestroy() {
super.onDestroy();
if (mIsServiceBound) {
unbindService(mServiceConnection);
mIsServiceBound = false;
}
}
最後在Activity加入按鈕，按鈕按下時就會從服務取得亂數
@Override
public void onClick(View v) {
int uiID = v.getId();
switch (uiID) {
case R.id.bind_service_get_service_random_number:
if (mIsServiceBound) {
Toast.makeText(this, "get Service random number:" + mBindService.getRandom(), Toast.LENGTH_SHORT).show();
}
break;
}
}
以下為完整程式碼
public class BindServiceActivity extends AppCompatActivity implements OnClickListener {
private BindService mBindService;
private boolean mIsServiceBound;
private Button mGetServiceRandomNumber;
private ServiceConnection mServiceConnection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName name, IBinder binder) {
ServiceBinder serviceBinder = (ServiceBinder) binder;
mBindService = serviceBinder.getBindService();
mIsServiceBound = true;
}
@Override
public void onServiceDisconnected(ComponentName name) {
mIsServiceBound = false;
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_bind_service);
mGetServiceRandomNumber = findViewById(R.id.bind_service_get_service_random_number);
mGetServiceRandomNumber.setOnClickListener(this);
Intent bindService = new Intent(this, BindService.class);
if (!mIsServiceBound) {
bindService(bindService, mServiceConnection, Context.BIND_AUTO_CREATE);
}
}
@Override
protected void onDestroy() {
super.onDestroy();
if (mIsServiceBound) {
unbindService(mServiceConnection);
mIsServiceBound = false;
}
}
@Override
public void onClick(View v) {
int uiID = v.getId();
switch (uiID) {
case R.id.bind_service_get_service_random_number:
if (mIsServiceBound) {
Toast.makeText(this, "get Service random number:" + mBindService.getRandom(), Toast.LENGTH_SHORT).show();
}
break;
}
}
}
public class BindService extends Service {
private IBinder mBinder = new ServiceBinder();
public BindService() {
}
public class ServiceBinder extends Binder {
public BindService getBindService() {
return BindService.this;
}
}
@Override
public IBinder onBind(Intent intent) {
return mBinder;
}
public int getRandom(){
return new Random().nextInt(100);
}
}
綁定型服務的生命週期
在BindService複寫onCreate, onBind, onStartCommand, onUnbind, onDestroy加入log來觀察生命週期。
public class BindService extends Service {
…
public BindService() {
Log.d(TAG, "BindService: ");
}
@Override
public void onCreate() {
Log.d(TAG, "onCreate: ");
super.onCreate();
}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
Log.d(TAG, "onStartCommand: ");
return super.onStartCommand(intent, flags, startId);
}
@Override
public IBinder onBind(Intent intent) {
Log.d(TAG, "onBind: ");
return mBinder;
}
@Override
public boolean onUnbind(Intent intent) {
Log.d(TAG, "onUnbind: ");
return super.onUnbind(intent);
}
@Override
public void onDestroy() {
Log.d(TAG, "onDestroy: ");
super.onDestroy();
}
…
}
在BindServiceActivity複寫onCreate, ServiceConnection的onServiceConnected, onServiceDisconnected加入log觀察生命週期
public class BindServiceActivity extends AppCompatActivity implements OnClickListener {
private static final String TAG = BindServiceActivity.class.getSimpleName();
private ServiceConnection mServiceConnection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName name, IBinder binder) {
ServiceBinder serviceBinder = (ServiceBinder) binder;
mBindService = serviceBinder.getBindService();
mIsServiceBound = true;
Log.d(TAG, "onServiceConnected: ");
}
@Override
public void onServiceDisconnected(ComponentName name) {
mIsServiceBound = false;
Log.d(TAG, "onServiceDisconnected: ");
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_bind_service);
mGetServiceRandomNumber = findViewById(R.id.bind_service_get_service_random_number);
mGetServiceRandomNumber.setOnClickListener(this);
Intent bindService = new Intent(this, BindService.class);
if (!mIsServiceBound) {
Log.d(TAG, "Activity call bindService: ");
bindService(bindService, mServiceConnection, Context.BIND_AUTO_CREATE);
}
}
@Override
protected void onDestroy() {
super.onDestroy();
if (mIsServiceBound) {
unbindService(mServiceConnection);
Log.d(TAG, "Activity call unbindService: ");
mIsServiceBound = false;
}
}
@Override
public void onClick(View v) {
int uiID = v.getId();
switch (uiID) {
case R.id.bind_service_get_service_random_number:
if (mIsServiceBound) {
Toast.makeText(this, "get Service random number:" + mBindService.getRandom(), Toast.LENGTH_SHORT).show();
}
break;
}
}
}
啟動Activity後的log為
D/BindServiceActivity: Activity call bindService: D/BindService: BindService: D/BindService: onCreate: D/BindService: onBind: D/BindServiceActivity: onServiceConnected:
需要注意的是onServiceConnected方法是在服務呼叫onBind方法之後呼叫
點擊back key之後的log為
D/BindServiceActivity: Activity call unbindService: D/BindService: onUnbind: D/BindService: onDestroy:
需要注意的是當元件透過呼叫unbindService去解綁定服務時， ServiceConnection的onServiceDisconnected方法不會被呼叫。
多個元件綁定和解綁定服務
綁定型服務可以和多個元件一起綁定。和多個元件綁定之後只有當所有的元件都解綁定該服務才會銷毀。
為了測試多個元件綁定服務，新增AnotherBindServiceActivity，如下
public class AnotherBindServiceActivity extends AppCompatActivity implements OnClickListener {
private static final String TAG = AnotherBindServiceActivity.class.getSimpleName();
private Button mBindServiceBtn;
private Button mUnbindServiceBtn;
private Button mGetRandomNumberBtn;
private Button mLaunchBindServiceActivityBtn;
private boolean mIsServiceBound;
private BindService mBindService;
private ServiceConnection mServiceConnection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName name, IBinder binder) {
ServiceBinder serviceBinder = (ServiceBinder) binder;
mBindService = serviceBinder.getBindService();
mIsServiceBound = true;
Log.d(TAG, "onServiceConnected: ");
}
@Override
public void onServiceDisconnected(ComponentName name) {
mIsServiceBound = false;
Log.d(TAG, "onServiceDisconnected: ");
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_another_bind_service);
mLaunchBindServiceActivityBtn = findViewById(R.id.another_bind_service_start_bind_service_activity);
mLaunchBindServiceActivityBtn.setOnClickListener(this);
mBindServiceBtn = findViewById(R.id.another_bind_service_bind_service);
mBindServiceBtn.setOnClickListener(this);
mUnbindServiceBtn = findViewById(R.id.another_bind_service_unbind_service);
mUnbindServiceBtn.setOnClickListener(this);
mGetRandomNumberBtn = findViewById(R.id.another_bind_service_get_service_random_number);
mGetRandomNumberBtn.setOnClickListener(this);
}
@Override
protected void onResume() {
super.onResume();
Log.d(TAG, "AnotherBindServiceActivity is:"+this.toString());
}
@Override
public void onClick(View v) {
int uiID = v.getId();
switch(uiID){
case R.id.another_bind_service_start_bind_service_activity:
Intent launchBindServiceActivity = new Intent(this, BindServiceActivity.class);
launchBindServiceActivity.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
startActivity(launchBindServiceActivity);
break;
case R.id.another_bind_service_bind_service:
Intent bindService = new Intent(this, BindService.class);
if (!mIsServiceBound) {
Log.d(TAG, "Activity call bindService: ");
bindService(bindService, mServiceConnection, Context.BIND_AUTO_CREATE);
}
break;
case R.id.another_bind_service_unbind_service:
if (mIsServiceBound) {
unbindService(mServiceConnection);
Log.d(TAG, "Activity call unbindService: ");
mIsServiceBound = false;
}
break;
case R.id.another_bind_service_get_service_random_number:
if (mIsServiceBound) {
Toast.makeText(this, "get Service random number:" + mBindService.getRandom()+" Service:"+mBindService.toString(), Toast.LENGTH_SHORT).show();
}else{
Toast.makeText(this, "Service not bind:", Toast.LENGTH_SHORT).show();
}
break;
}
}
}
重點在於AnotherBindServiceActivity也可綁定BindService，目前有BindServiceActivity和AnotherBindServiceActivity可綁定BindService。
另外修改BindServiceActivity新增按鍵用來綁定和解綁定以及啟動AnotherBindServiceActivity，如下
public class BindServiceActivity extends AppCompatActivity implements OnClickListener {
private static final String TAG = BindServiceActivity.class.getSimpleName();
private BindService mBindService;
private boolean mIsServiceBound;
private Button mGetServiceRandomNumberBtn;
private Button mtBindServiceBtn;
private Button mtUnBindServiceBtn;
private Button mStartAnotherBindServiceActivityBtn;
private ServiceConnection mServiceConnection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName name, IBinder binder) {
ServiceBinder serviceBinder = (ServiceBinder) binder;
mBindService = serviceBinder.getBindService();
mIsServiceBound = true;
Log.d(TAG, "onServiceConnected: ");
}
@Override
public void onServiceDisconnected(ComponentName name) {
mIsServiceBound = false;
Log.d(TAG, "onServiceConnected: ");
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_bind_service);
mGetServiceRandomNumberBtn = findViewById(R.id.bind_service_get_service_random_number);
mGetServiceRandomNumberBtn.setOnClickListener(this);
mtBindServiceBtn = findViewById(R.id.bind_service_bind_service);
mtBindServiceBtn.setOnClickListener(this);
mtUnBindServiceBtn = findViewById(R.id.bind_service_unbind_service);
mtUnBindServiceBtn.setOnClickListener(this);
mStartAnotherBindServiceActivityBtn = findViewById(R.id.bind_service_start_another_bind_service_activity);
mStartAnotherBindServiceActivityBtn.setOnClickListener(this);
}
@Override
protected void onResume() {
super.onResume();
Log.d(TAG, "BindServiceActivity is:"+this.toString());
}
@Override
protected void onDestroy() {
super.onDestroy();
}
@Override
public void onClick(View v) {
int uiID = v.getId();
switch (uiID) {
case R.id.bind_service_get_service_random_number:
if (mIsServiceBound) {
Toast.makeText(this, "get Service random number:" + mBindService.getRandom()+" Service:"+mBindService.toString(), Toast.LENGTH_SHORT).show();
}else{
Toast.makeText(this, "Service not bind:", Toast.LENGTH_SHORT).show();
}
break;
case R.id.bind_service_bind_service:
Intent bindService = new Intent(this, BindService.class);
if (!mIsServiceBound) {
Log.d(TAG, "Activity call bindService: ");
bindService(bindService, mServiceConnection, Context.BIND_AUTO_CREATE);
}
break;
case R.id.bind_service_unbind_service:
if (mIsServiceBound) {
unbindService(mServiceConnection);
Log.d(TAG, "Activity call unbindService: ");
mIsServiceBound = false;
}
break;
case R.id.bind_service_start_another_bind_service_activity:
Intent launchAnotherBindServiceActivity = new Intent(this, AnotherBindServiceActivity.class);
launchAnotherBindServiceActivity.setFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
startActivity(launchAnotherBindServiceActivity);
break;
}
}
}
注意BindServiceActivity和AnotherBindServiceActivity是透過FLAG_ACTIVITY_REORDER_TOFRONT來互相切換，並不是產生新的Activity實體。
現在先啟動BindServiceActivity並點擊bind service按鈕，Log如下
D/BindServiceActivity: Activity call bindService: D/BindService: BindService: D/BindService: onCreate: D/BindService: onBind: D/BindServiceActivity: onServiceConnected:
可以看出服務已被綁定，接著點擊按鈕啟動AnotherBindServiceActivity並在該Activity中點擊bind service按鈕，Log如下
D/AnotherBindServiceActivity: Activity call bindService: D/AnotherBindServiceActivity: onServiceConnected:
AnotherBindServiceActivity綁定服務之後服務不會再呼叫建構式以及onCreate, onBind方法，因為該服務已啟動。
接著點擊AnotherBindServiceActivity的unbind service按鈕，Log如下
D/AnotherBindServiceActivity: Activity call unbindService:
可以看到該服務並未銷毀，只是和AnotherBindServiceActivity解綁定。
接著按下start BindServiceActivity按鈕來啟動BindServiceActivity，啟動之後點擊unbind service按鈕，Log如下。
D/BindServiceActivity: Activity call unbindService: D/BindService: onUnbind: D/BindService: onDestroy:
這時候因為所有和該服務綁定的元件都解綁定服務，服務銷毀。
綁定型服務的優缺點
綁定型服務的優點在於可以和多個元件互動，傳遞訊息。
缺點在於服務本身的執行也是在UI Thread中，沒有另外開啟新的執行緒來執行
