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由于项目需要，我们有时候需要在service中处理耗时操作，然后将结果发送给activity以更新状态。通常情况下，只需要在一个service与一个activity之间通信，这种情况下，我们使用最多的是通过回调接口。具体做法是在service中定义一个接口，在activity中实现改接口，并通过bindservice来传入。当需要将service中的结果一次发送给多个activity时，我们又该如何实现呢？经过检索，存在三种实现的方式，分别是回调接口、广播接收者和观察者模式 。

• Service.java

package com.example.servicecallback;import android.app.Service;import android.content.Intent;import android.os.Binder;import android.os.IBinder;public class ContentService extends Service {
     @Override  public IBinder onBind(Intent arg0) {    // TODO Auto-generated method stub    return new LocalBinder();  }  @Override  public void onCreate() {    // TODO Auto-generated method stub    super.onCreate();  }  public final class LocalBinder extends Binder {
       public ContentService getService() {      return ContentService.this;    }  }  public void asyncSendPerson(final String name) {    // 休息5秒，模拟异步任务    new Thread(new Runnable() {      @Override      public void run() {        try {          Thread.sleep(5000);        } catch (InterruptedException e) {          e.printStackTrace();        }        //可以在子线程中直接发送广播        sendContentBroadcast(name);      }    }).start();  }  /**   * 发送广播   * @param name   */  protected void sendContentBroadcast(String name) {    // TODO Auto-generated method stub    Intent intent=new Intent();    intent.setAction("com.example.servicecallback.content");    intent.putExtra("name", name);    sendBroadcast(intent);  }}

• MainActivity.java

package com.example.servicecallback;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.Menu;import android.view.View;import android.view.View.OnClickListener;import android.widget.TextView;public class MainActivity extends Activity {
     private MyServiceConn conn;  private TextView mContent;  private ContentReceiver mReceiver;  @Override  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.activity_main);    conn = new MyServiceConn();    bindService(new Intent(this, ContentService.class), conn,        BIND_AUTO_CREATE);    mContent = (TextView) findViewById(R.id.content);    this.findViewById(R.id.button1).setOnClickListener(        new OnClickListener() {          @Override          public void onClick(View v) {            // TODO Auto-generated method stub            startActivity(new Intent(MainActivity.this,                OtherActivity.class));          }        });    doRegisterReceiver();  }  /**   * 注册广播接收者   */  private void doRegisterReceiver() {    mReceiver=new ContentReceiver();    IntentFilter filter = new IntentFilter(        "com.example.servicecallback.content");    registerReceiver(mReceiver, filter);  }  @Override  public boolean onCreateOptionsMenu(Menu menu) {    // Inflate the menu; this adds items to the action bar if it is present.    getMenuInflater().inflate(R.menu.main, menu);    return true;  }  public class MyServiceConn implements ServiceConnection {
       @Override    public void onServiceConnected(ComponentName name, IBinder binder) {      // service = ((LocalBinder) binder).getService();    }    @Override    public void onServiceDisconnected(ComponentName name) {      // TODO Auto-generated method stub      // service = null;    }  }  @Override  protected void onDestroy() {    // TODO Auto-generated method stub    super.onDestroy();    unbindService(conn);    if (mReceiver!=null) {      unregisterReceiver(mReceiver);    }  }  public class ContentReceiver extends BroadcastReceiver {
       @Override    public void onReceive(Context context, Intent intent) {      String name = intent.getStringExtra("name");      Person person = new Person();      person.setName(name);      mContent.setText(person.toString());    }  }}

• OtherActivity.java

package com.example.servicecallback;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.view.View.OnClickListener;import android.widget.Button;import android.widget.EditText;import android.widget.TextView;import com.example.servicecallback.ContentService.LocalBinder;public class OtherActivity extends Activity {
     private ContentService service;  private TextView mContent;  private Button mSubmit;  private EditText mEditText;  private ServiceConnection conn;  private ContentReceiver mReceiver;  @Override  protected void onCreate(Bundle savedInstanceState) {    super.onCreate(savedInstanceState);    setContentView(R.layout.other);    mEditText = (EditText) findViewById(R.id.edittext);    mSubmit = (Button) findViewById(R.id.button1);    mContent = (TextView) findViewById(R.id.content);    mSubmit.setOnClickListener(new OnClickListener() {      @Override      public void onClick(View v) {        String name = mEditText.getText().toString();        service.asyncSendPerson(name);      }    });    conn=new MyServiceConn();    bindService(new Intent(OtherActivity.this, ContentService.class), conn,        BIND_AUTO_CREATE);    doRegisterReceiver();  }  private void doRegisterReceiver() {    mReceiver=new ContentReceiver();    IntentFilter filter = new IntentFilter(        "com.example.servicecallback.content");    registerReceiver(mReceiver, filter);  }  public final class MyServiceConn implements ServiceConnection {
       @Override    public void onServiceConnected(ComponentName name, IBinder binder) {      service = ((LocalBinder) binder).getService();    }    @Override    public void onServiceDisconnected(ComponentName name) {      service = null;    }  }  @Override  protected void onDestroy() {    super.onDestroy();    unbindService(conn);    if (mReceiver!=null) {      unregisterReceiver(mReceiver);    }  }  public class ContentReceiver extends BroadcastReceiver {
       @Override    public void onReceive(Context context, Intent intent) {      String name = intent.getStringExtra("name");      Person person = new Person();      person.setName(name);      mContent.setText(person.toString());    }  }}

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