Android App后台服务报告工作状态实例
本节讲运行在后台服务里的工作请求，如何向发送请求者报告状态。推荐用LocalBroadcastManager发送和接收状态，它限制了只有本app才能接收到广播。
从IntentService汇报状态
从IntentService发送工作请求状态给其他组件，先创建一个包含状态和数据的Intent。也可以添加action和URI到intent里。
下一步，调用LocalBroadcastManager.sendBroadcast()发送Intent,应用中所有注册了接收该广播的接收器都能收到。LocalBroadcastManager.getInstance()获取LocalBroadcastManager实例。
publicfinalclassConstants{
...
//DefinesacustomIntentaction
publicstaticfinalStringBROADCAST_ACTION=
"com.example.android.threadsample.BROADCAST";
...
//Definesthekeyforthestatus"extra"inanIntent
publicstaticfinalStringEXTENDED_DATA_STATUS=
"com.example.android.threadsample.STATUS";
...
}
publicclassRSSPullServiceextendsIntentService{
...
/*
*CreatesanewIntentcontainingaUriobject
*BROADCAST_ACTIONisacustomIntentaction
*/
IntentlocalIntent=
newIntent(Constants.BROADCAST_ACTION)
//PutsthestatusintotheIntent
.putExtra(Constants.EXTENDED_DATA_STATUS,status);
//BroadcaststheIntenttoreceiversinthisapp.
LocalBroadcastManager.getInstance(this).sendBroadcast(localIntent);
...
}
下一步是接收广播并处理。
接收来自IntentService的广播
接收方式与普通的Broadcast一样，用一个BroadcastReceiver的子类，实现BroadcastReceiver.onReceive()方法
//BroadcastreceiverforreceivingstatusupdatesfromtheIntentService
privateclassResponseReceiverextendsBroadcastReceiver
{
//Preventsinstantiation
privateDownloadStateReceiver(){
}
//CalledwhentheBroadcastReceivergetsanIntentit'sregisteredtoreceive
@
publicvoidonReceive(Contextcontext,Intentintent){
...
/*
*HandleIntentshere.
*/
...
}
}定义好了接收器类以后，定义过滤器，匹配指定的action,categorie,data.
//Classthatdisplaysphotos
publicclassDisplayActivityextendsFragmentActivity{
...
publicvoidonCreate(BundlestateBundle){
...
super.onCreate(stateBundle);
...
//Thefilter'sactionisBROADCAST_ACTION
IntentFiltermStatusIntentFilter=newIntentFilter(
Constants.BROADCAST_ACTION);
//AddsadatafilterfortheHTTPscheme
mStatusIntentFilter.addDataScheme("http");
...
注册方式稍有不同，用LocalBroadcastManager.registerReceiver()。
//InstantiatesanewDownloadStateReceiver
DownloadStateReceivermDownloadStateReceiver=
newDownloadStateReceiver();
//RegisterstheDownloadStateReceiveranditsintentfilters
LocalBroadcastManager.getInstance(this).registerReceiver(
mDownloadStateReceiver,
mStatusIntentFilter);
...单个BroadcastReceiver可以处理多种类型的广播，这个特性允许你根据不同的action运行不同的代码，而无需为每个action定义一个BroadcastReceiver。
/*
*Instantiatesanewactionfilter.
*Nodatafilterisneeded.
*/
statusIntentFilter=newIntentFilter(Constants.ACTION_ZOOM_IMAGE);
...
//Registersthereceiverwiththenewfilter
LocalBroadcastManager.getInstance(getActivity()).registerReceiver(
mDownloadStateReceiver,
mIntentFilter);发送广播并不会启动或恢复Activity.BroadcastReceiver让Activity能够接收处理数据，包括应用在后台的时候，但不会强制app回到前台。如果你要在app在后台，对用户不可见时，通知用户一个事件发生，用Notification。绝对不要启动一个Activity来响应广播。