Service簡介:
Service 是Android的四大組件之一,一般用於沒有UI界面,長期執行的後臺任務,即使程序退出時,後臺任務還在執行。比如:音樂播放。
Service的誤區:
1.service在UI線程中執行。 2.不可以在service中執行耗時任務,因為service是在UI線程中運行的。 3.如果需要執行後臺的耗時任務,必須在Service中開啟一個線程來執行。
Service的生命周期:
啟動和停止Service的兩種方式 1.context.startService();context.stopService(). 2.context.bindService();context.unbindService().
Service使用實例1:
客戶端代碼如下:
package com.xjp.broadcast; import android.app.Activity; import android.content.BroadcastReceiver; import android.content.Context; import android.content.Intent; import android.content.IntentFilter; import android.os.Bundle; import android.view.View; import android.widget.Button; import android.widget.TextView; public class MainActivity extends Activity { private final static String action = "com.xjp.MainActivity"; private TextView result; private Button startService; private Button stopService; private BroadcastReceiver broadcastReceiver = new BroadcastReceiver() { @Override public void onReceive(Context context, Intent intent) { int i = intent.getIntExtra("key", 0); result.setText(i + ""); } }; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); result = (TextView) findViewById(R.id.result); startService = (Button) findViewById(R.id.startService); startService.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Intent service = new Intent(MainActivity.this, CalculationService.class); startService(service); } }); stopService = (Button) findViewById(R.id.stopService); stopService.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Intent service = new Intent(MainActivity.this, CalculationService.class); stopService(service); } }); } @Override protected void onResume() { super.onResume(); initFilter(); } @Override protected void onDestroy() { super.onDestroy(); unregisterReceiver(broadcastReceiver); } private void initFilter() { IntentFilter filter = new IntentFilter(); filter.addAction(action); registerReceiver(broadcastReceiver, filter); } }
1.依次點擊“啟動服務” 和“停止服務” ,生命周期 打印結果如下:
2.點擊兩次 “啟動服務” 打印結果如下:
這種方式可以多次啟動同一個Service,並且 隻有第一次才執行 onCreate。第二次之後 就隻執行 onStartCommand,並且當且僅當該應用退出之後,該服務依然存在後臺運行著。退出之後,在設置裡面查看正在運行的應用:
服務端代碼如下:
package com.xjp.broadcast; import android.app.Service; import android.content.Intent; import android.os.IBinder; import android.util.Log; /** * Description: * User: xjp * Date: 2015/5/4 * Time: 14:14 */ public class CalculationService extends Service { private final static String TAG = "CalculationService"; private final static String action = "com.xjp.MainActivity"; private boolean quit = false; @Override public IBinder onBind(Intent intent) { Log.e(TAG, "====onBind====="); return null; } @Override public boolean onUnbind(Intent intent) { Log.e(TAG, "====onUnbind====="); return super.onUnbind(intent); } @Override public void onCreate() { Log.e(TAG, "====onCreate====="); super.onCreate(); } @Override public int onStartCommand(Intent intent, int flags, int startId) { Log.e(TAG, "====onStartCommand====="); startThread(); return super.onStartCommand(intent, flags, startId); } @Override public void onDestroy() { Log.e(TAG, "====onDestroy====="); quit = true; super.onDestroy(); } /** * 開啟線程模擬耗時任務 */ public void startThread() { new Thread(new Runnable() { int i = 0; @Override public void run() { while (i < 200 && !quit) { try { Thread.sleep(1000); i++; Intent intent = new Intent(action); intent.putExtra("key", i); sendBroadcast(intent); } catch (InterruptedException e) { e.printStackTrace(); } } } }).start(); } }
Service使用實例2:
客戶端代碼如下:
package com.xjp.broadcast; import android.app.Activity; import android.content.BroadcastReceiver; import android.content.ComponentName; import android.content.Context; import android.content.Intent; import android.content.IntentFilter; import android.content.ServiceConnection; import android.os.Bundle; import android.os.IBinder; import android.view.View; import android.widget.Button; import android.widget.TextView; public class MainActivity extends Activity { private final static String action = "com.xjp.MainActivity"; private TextView result; private Button startService; private Button stopService; private CalculationService calculationService; private BroadcastReceiver broadcastReceiver = new BroadcastReceiver() { @Override public void onReceive(Context context, Intent intent) { int i = intent.getIntExtra("key", 0); result.setText(i + ""); } }; private ServiceConnection serviceConnection = new ServiceConnection() { @Override public void onServiceConnected(ComponentName name, IBinder service) { calculationService = ((CalculationService.CalulationBinder) service).getService(); calculationService.startThread(); } @Override public void onServiceDisconnected(ComponentName name) { calculationService = null; } }; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); result = (TextView) findViewById(R.id.result); startService = (Button) findViewById(R.id.startService); startService.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { Intent service = new Intent(MainActivity.this, CalculationService.class); bindService(service, serviceConnection, Context.BIND_AUTO_CREATE); } }); stopService = (Button) findViewById(R.id.stopService); stopService.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { unbindService(serviceConnection); } }); } @Override protected void onResume() { super.onResume(); initFilter(); } @Override protected void onDestroy() { super.onDestroy(); unregisterReceiver(broadcastReceiver); } private void initFilter() { IntentFilter filter = new IntentFilter(); filter.addAction(action); registerReceiver(broadcastReceiver, filter); } }
服務端代碼如下:
package com.xjp.broadcast; import android.app.Service; import android.content.Intent; import android.os.Binder; import android.os.IBinder; import android.util.Log; /** * Description: * User: xjp * Date: 2015/5/4 * Time: 14:14 */ public class CalculationService extends Service { private final static String TAG = "CalculationService"; private final static String action = "com.xjp.MainActivity"; private boolean quit = false; private IBinder binder = new CalulationBinder(); public class CalulationBinder extends Binder { public CalculationService getService() { return CalculationService.this; } } @Override public IBinder onBind(Intent intent) { Log.e(TAG, "====onBind====="); return binder; } @Override public boolean onUnbind(Intent intent) { Log.e(TAG, "====onUnbind====="); return super.onUnbind(intent); } @Override public void onCreate() { Log.e(TAG, "====onCreate====="); super.onCreate(); } @Override public int onStartCommand(Intent intent, int flags, int startId) { Log.e(TAG, "====onStartCommand====="); startThread(); return super.onStartCommand(intent, flags, startId); } @Override public void onDestroy() { Log.e(TAG, "====onDestroy====="); quit = true; super.onDestroy(); } /** * 開啟線程模擬耗時任務 */ public void startThread() { new Thread(new Runnable() { int i = 0; @Override public void run() { while (i < 200 && !quit) { try { Thread.sleep(1000); i++; Intent intent = new Intent(action); intent.putExtra("key", i); sendBroadcast(intent); } catch (InterruptedException e) { e.printStackTrace(); } } } }).start(); } }
一次點擊“啟動服務”按鈕和 “停止服務” 按鈕,生命周期 打印結果如下:
綁定服務,如果退出的時候沒有解除綁定 ,也就是沒有調用 context.unbindService().的話,會報錯誤。所以,一般都在客戶端的 onDestory()中調用 context.unbindService(). 所以這種服務不太適合後臺長時間的任務。 這種服務綁定和解除綁定是成對出現的。
兩種Service總結:
第一種,非綁定的Service,應用退出時可以不停止服務退出。可以讓服務一直在後臺運行。缺點:啟動服務即 啟動後臺任務,不能很好的在客戶端隨時控制 服務的後臺任務執行時間。 第二種,綁定的Service,應用退出時必須解除綁定Service,否則程序報錯。優點:不過綁定的Service可獲得 Service 的Binder,可以靈活控制 Service裡的各種方法的調用。