Android Service 与 Activity使用Pending Intent通信
service使用pending intent返回结果给客户端
我们使用一个activity作为一个客户端，来通过startService()的方法启动一个服务，这个服务的功能很简单，就是去访问客户端指定的Url，然后返回这个url对应的页面的源代码的字符数量。这个例子中，我们是不允许这个服务被绑定的。即我们在onBind()方法中返回null。那么好了，现在我们这个服务不可以被绑定，只可以通过startService()的方法启动，那么此时服务和客户端的通信方式就只有一种了，即通过Pending Intent了。
1.首先自定义我们的服务类：MyService
public class MyService extends Service {
private ServiceHandler mHandler;
//内部类
private final class ServiceHandler extends Handler{
public ServiceHandler(Looper looper){
super(looper);
}
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
if(msg.what == 0x1234){
Log.v("MyService","handleMessage()被调用");
int charNum = ((String)(msg.obj)).length();
Bundle bundle = msg.getData();
PendingIntent client = bundle.getParcelable("receiver");
Log.v("MyService","字符数为" + charNum);
Intent intent = new Intent();
intent.putExtra("CHARNUM",charNum);
try {
client.send(getApplicationContext(),0,intent);
Log.v("MyService","广播发送完成");
} catch (PendingIntent.CanceledException e) {
e.printStackTrace();
}
}
}
}
@Override
public void onCreate() {
super.onCreate();
mHandler = new ServiceHandler(this.getMainLooper());
Log.v("MyService","onCreate()被调用");
}
@Override
public int onStartCommand(final Intent intent, int flags, final int startId) {
Log.v("MyService","onStartCommand()被调用");
final String urlString = intent.getStringExtra("URL");
new Thread(){
@Override
public void run() {
try {
String result = null;
BufferedReader in = null ;
URL url = new URL(urlString);
URLConnection conn = url.openConnection();
conn.connect();//建立连接
in = new BufferedReader(new InputStreamReader(conn.getInputStream()));
String line = null;
while ((line = in.readLine()) != null ){
result += "
" + line;
}
Log.v("URL请求结果",result);
//发送消息
Message msg = new Message();
msg.what = 0x1234;
msg.arg1 = startId;
msg.obj = result;
msg.setData(intent.getExtras());
mHandler.sendMessage(msg);
} catch (IOException e) {
e.printStackTrace();
}
}
}.start();
return super.onStartCommand(intent, flags, startId);
}
@Nullable
@Override
public IBinder onBind(Intent intent) {
Log.v("MyService","onBind()被调用");
return null;
}
}
对于每一个startService()请求，我们都开启了一个新的线程去访问指定的额URL，并对字符串计数。服务里面最重要的便是自定义的Handler里面的handleMessage()方法了，这个方法里面我们取出client传给服务的intent，然后在这个intent里面取出序列化的pendingintent，然后再将其反序列化成为pending intent对象。最后理由这个客户端定义好的pending intent，给广播接受者发送广播，当然广播内容便是我们需要返回给客户端的的结果了。
2.MainActivity类
public class MainActivity extends AppCompatActivity implements View.OnClickListener,MyBroadcastReceiver.onServiceResultReturnListener{
Button btnStartService,btnBindService,btnStartServiceForResult;
MyBroadcastReceiver receiver;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
btnStartServiceForResult = (Button)findViewById(R.id.id_btn_startServiceForResult);
btnStartServiceForResult.setOnClickListener(this);
//初始化广播接受者
initBroadcastReceiver();
}
@Override
public void onClick(View view) {
switch (view.getId()){
case R.id.id_btn_startServiceForResult:
Intent sfIntent = new Intent(this,MyService.class);
Intent broadIntent = new Intent();
broadIntent.setAction("cn.edu.dlut.receiver");
PendingIntent pIntent = PendingIntent.getBroadcast(this,0,broadIntent,0);
Bundle bundle = new Bundle();
bundle.putParcelable("receiver",pIntent);
sfIntent.putExtras(bundle);
sfIntent.putExtra("URL","http://www.baidu.com");
startService(sfIntent);
Log.v("MainActivity","startService()方法被调用");
break;
}
}
//初始化广播接收者
private void initBroadcastReceiver(){
receiver = new MyBroadcastReceiver(this);
this.registerReceiver(receiver,new IntentFilter("cn.edu.dlut.receiver"));
Log.v("MainActivity","广播接受者动态注册初始化完成");
}
@Override
protected void onDestroy() {
super.onDestroy();
this.unregisterReceiver(receiver);
}
@Override
public void onServiceResultReturn(Intent intent) {
int charNum = intent.getIntExtra("CHARNUM",0);
Toast.makeText(this,"字符数为" + charNum,Toast.LENGTH_SHORT).show();
}
}
//自定义广播接受者
class MyBroadcastReceiver extends BroadcastReceiver{
//回调接口
public interface onServiceResultReturnListener{
void onServiceResultReturn(Intent intent);
}
private onServiceResultReturnListener client;
public MyBroadcastReceiver(onServiceResultReturnListener client){
this.client = client;
}
@Override
public void onReceive(Context context, Intent intent) {
Log.v("MyBroadcaseReceiver","onReceive()方法被调用");
this.client.onServiceResultReturn(intent);
}
}
demo程序源代码，已上传至git上面https://github.com/Spground/ServiceDemo
3.总结
利用pending intent作为started service(即用startService()启动的服务)与client通信的步骤大致如下：
1.实现自己的Service类，并取得client传递过来的intent,因为这个intent里面包含我们序列化的pending intent。
2.自定义广播接受者，并在client端动态注册广播接收者(静态注册也可以，只要广播接受者收到消息后会通知到client)
3.定义好client与广播接受者通信的回调接口
4.在client端调用startService()方法启动服务的时候，讲pending intent准备好，并将其序列化作为Extras放进入启动服务的intent中.
总的来说，使用这种方式来进行服务 和 client通信是十分繁琐的，后面有绑定服务运行方式，会在绑定成功以后给client一个实现了IBinder的实例，
通过让服务实现IBinder接口，便可以将服务的实例的引用作为返回值传递给client，client便可以用这个接口与服务通信了，当然也还是可用使用广播的形式让服务与client通信。