何时使用 Service、AsyncTask 或 Handler? [英] When to use a Service or AsyncTask or Handler?

问题描述

谁能告诉我真正的区别?

推荐答案

我的经验法则是，AsyncTask 适用于我想做与单个 Activity 和 Service 用于当我想做一些事情时，它会在启动它的 Activity 在后台进行.

My rule of thumb is that an AsyncTask is for when I want to do something tied to single Activity and a Service is for when I want to do something that will carry on after the Activity which started it is in the background.

因此，如果我想在 Activity 中进行少量后台处理而不占用 UI，我将使用 AsyncTask.然后，我将使用该 Activity 中的默认 Handler 将消息传回以确保更新发生在主线程上.在主线程上处理更新有两个好处:UI 更新正确发生，您不必太担心同步问题.

So if I want to do a small bit of background processing in the Activity without tying up the UI I'll use an AsyncTask. I'll then use the default Handler from that Activity to pass messages back to ensure updates happen on the main thread. Processing the updates on the main thread has two benefits: UI updates happen correctly and you don't have to worry so much about synchronisation problems.

例如，如果我想做一个可能需要一段时间的下载，我会使用Service.因此，如果我转到应用程序中的另一个 Activity 或其他应用程序，我的 Service 可以继续运行并继续下载文件，以便在我返回应用程序时准备就绪.在这种情况下，我可能会使用 状态栏通知 下载完成后，用户可以选择在方便时返回我的应用程序.

If for example, I wanted to do a download which might take a while I'd use a Service. So if I went to another Activity in my application or another application entirely my Service could keep running and keep downloading the file so it would be ready when I returned to my application. In this case I'd probably use a Status Bar Notification once the download was complete, so the user could choose to return to my application whenever was convenient for them.

如果您将 AsyncTask 用于长时间运行的进程，您会发现它在您离开 Activity 后可能会继续，但是:

What you'll find if you use an AsyncTask for a long-running process it may continue after you've navigated away from the Activity but:

• 如果处理完成时 Activity 在后台，当您尝试使用结果等更新 UI 时可能会遇到问题.
• 后台Activity在需要内存时比Service更有可能被Android杀死.

• If the Activity is in the background when your processing is complete you may have problems when you try to update the UI with the results etc.
• A background Activity is far more likely to be killed by Android when it needs memory than a Service.

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