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。

public final class constants {
    ...
    // defines a custom intent action
    public static final string broadcast_action =
        "com.example.android.threadsample.broadcast";
    ...
    // defines the key for the status "extra" in an intent
    public static final string extended_data_status =
        "com.example.android.threadsample.status";
    ...
}
public class rsspullservice extends intentservice {
...
    /*
     * creates a new intent containing a uri object
     * broadcast_action is a custom intent action
     */
    intent localintent =
            new intent(constants.broadcast_action)
            // puts the status into the intent
            .putextra(constants.extended_data_status, status);
    // broadcasts the intent to receivers in this app.
    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

// broadcast receiver for receiving status updates from the intentservice
private class responsereceiver extends broadcastreceiver
{
    // prevents instantiation
    private downloadstatereceiver() {
    }
    // called when the broadcastreceiver gets an intent it's registered to receive
    @
    public void onreceive(context context, intent intent) {
...
        /*
         * handle intents here.
         */
...
    }
}

定义好了接收器类以后，定义过滤器，匹配指定的action,categorie,data.

// class that displays photos
public class displayactivity extends fragmentactivity {
    ...
    public void oncreate(bundle statebundle) {
        ...
        super.oncreate(statebundle);
        ...
        // the filter's action is broadcast_action
        intentfilter mstatusintentfilter = new intentfilter(
                constants.broadcast_action);
 
        // adds a data filter for the http scheme
        mstatusintentfilter.adddatascheme("http");
        ...

注册方式稍有不同，用localbroadcastmanager.registerreceiver()。

  // instantiates a new downloadstatereceiver
        downloadstatereceiver mdownloadstatereceiver =
                new downloadstatereceiver();
        // registers the downloadstatereceiver and its intent filters
        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。

  /*
         * instantiates a new action filter.
         * no data filter is needed.
         */
        statusintentfilter = new intentfilter(constants.action_zoom_image);
        ...
        // registers the receiver with the new filter
        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。