使用IntentService下载数据 - 生命周期的变化 [英] Downloading data using IntentService - Lifecycle changes

问题描述

铊;博士如何知道什么时候一个 IntentService 已完成下载后返回到活动使用监听其结果广播接收器？

Tl;dr How to know when an IntentService has finished downloading upon returning to the Activity which listens to its result using a BroadcastReceiver?

我要搬到实现数据下载到 IntentService S，并通知当任务使用完广播接收器秒。

I'm moving to implementing data downloading to IntentServices, and notifying when the task has finished using BroadcastReceivers.

我一般启动该服务在我的活动：

I generally start the service in my Activity:

IntentFilter intentFilter = DownloadDataService.startDownloadData(this);
getLocalBroadcastManager().registerReceiver(mBroadcastReceiver, intentFilter);

这是启动服务部分：

/**
 * Starts the service and returns an IntentFilter to subscribe a BroadcastReceiver on. 
 * When the task has finished, a broadcast for returned IntentFilter is sent,
 * containing downloaded data.
 */
public static IntentFilter startDownloadData(final Context context) {
    Intent intent = new Intent(context, DownloadDataService.class);
    intent.setAction(ACTION_DOWNLOAD_DATA);
    context.startService(intent);

    return new IntentFilter(ACTION_DOWNLOAD_DATA);
}

当然， onHandleIntent（意向）（简体）：

@Override
protected void onHandleIntent(final Intent intent){
    Data data = downloadData();
    Intent intent = new Intent(ACTION_DOWNLOAD_DATA);
    intent.putExtra(DATA, data);
    LocalBroadcastManager.getInstance(this).sendBroadcast(intent);
}

这一切运作良好，我能保持状态在我的活动来知道例如改变方向后，我是否在等待下载的数据结果：

This all works well, and I can keep states in my Activity to know for example after an orientation change whether I was waiting for a download data result:

@Override
public void onResume(){
    super.onResume();
    if (mState == State.DOWNLOADING) {
        Log.v(TAG, "Registering receiver for existing download data");
        IntentFilter intentFilter = DownloadDataService.getIntentFilter();
        getLocalBroadcastManager().registerReceiver(mBroadcastReceiver, intentFilter);
    }
}

太好了，现在我也可以处理方向变化。只有一个问题留给：

Great, now I can also handle orientation changes. Only one problem left:

• 活动启动 DownloadDataService


• 用户从活动移开


• DownloadDataService 广播其完成的消息（这不是由活动收到由于 unregisterReceiver 在的onStop（））


• 用户移动回活动


• 活动仍然认为它是等待 DownloadDataService ，和什么也不做。

• Activity starts the DownloadDataService
• User moves away from the Activity
• DownloadDataService broadcasts its done message (which is not received by the Activity due to unregisterReceiver in onStop())
• User moves back into the Activity
• Activity still thinks it's waiting for the DownloadDataService, and does nothing.

我该如何弥补呢？

请注意，我没有这样用于存储下载的数据数据库的任何持久性。在活动从检索数据广播意图。

Note that I do not have any persistence like databases for storing the downloaded data. The Activity retrieves the data from the broadcasted Intent.

注2：有这个答案来的问题如何知道是否服务正在运行。虽然这可能会奏效，但明确表示，该方法是调试或实施服务管理型的用户界面的

Note #2: There is this answer to the question of how to know whether a Service is running. Although this might work, it is explicitly stated that that method is for debugging or implementing service management type user interfaces.

推荐答案

我是不是真的通过使用共享preferences，静态变量和其他哈克的解决方案信服。

I wasn't really convinced by using SharedPreferences, static variables and other 'hacky' solutions.

我也不过发现你可以提供一个 ResultReceiver - 这是parcelable - 你可以用它来通知你的任务就完成了。它接收一个处理程序来指定线程结果的处理上。

I did find however that you can supply a ResultReceiver - which is parcelable - which you can use to notify your task is finished. It receives a Handler to specify the thread the result is handled on.

这样做的好处是，你可以在的onSaveInstanceState 保存 ResultReceiver 。使用一些聪明的你一定可以使这项工作。我创建了有利于这种战术的实验库： https://github.com/nhaarman/Ergo

The advantage of this, is that you can save the ResultReceiver during onSaveInstanceState. Using some clever tricks you can certainly make this work. I have created an experimental library which facilitates this tactic: https://github.com/nhaarman/Ergo

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