如果它在android的同一线程中运行，为什么要使用Service [英] Why use Service if it runs in the same thread in android

问题描述

我正在通过Android Developer网站中的绑定服务.我以为我对服务足够了解，但是我发现了另一种通过使用 类，尤其适用于本地服务.在那里，我感到困惑.也许我把这个概念弄错了.

I was going through Bound Service in Android Developer website. I thought I understood the service enough but I just found another way of connecting service through Using a Messenger class especially for local service. There I got confused. Maybe I got the concept wrong.

这是我对Android Service 的理解.您在以下时间创建服务

Here is my understanding of Android Service. You create a service when

1. 您想在后台中进行单独的工作.
2. 您要使其成为一个单独的过程.
3. 您想使它在独立于启动它的组件的生命周期中运行.

1. You want to do separate jobs in the background.
2. You want to make it a separate process.
3. You want to make it run in a lifecycle that's independent of the component that started it.

混淆是列表中的第一项，即背景的定义.后台不是线程还是进程?我从没想过它可以在主线程上运行.

Confusion is the first item in the list, the definition of the background. Isn't the background a thread or process? I never thought that it can run on the main thread.

这是有关开发页面中的服务警告.

Here is the caution of service in the dev pages about.

警告:服务在其宿主进程的主线程中运行-该服务不会创建自己的线程，也不会在单独的进程中运行(除非您另行指定).这意味着，如果您的服务要执行任何CPU密集型工作或阻止操作(例如MP3播放或联网)，则应在服务内创建一个新线程来执行该工作.通过使用单独的线程，可以降低应用程序无响应(ANR)错误的风险，并且应用程序的主线程可以保持专用于用户与活动的交互.

Caution: A service runs in the main thread of its hosting process—the service does not create its own thread and does not run in a separate process (unless you specify otherwise). This means that, if your service is going to do any CPU intensive work or blocking operations (such as MP3 playback or networking), you should create a new thread within the service to do that work. By using a separate thread, you will reduce the risk of Application Not Responding (ANR) errors and the application's main thread can remain dedicated to user interaction with your activities.

问题

1. 如果服务功能仍将在主线程上运行，为什么选择使用服务?
2. 即使耗时的工作在主线程中完成，我们是否也仅需编写服务来阻止ANR?假定该服务仅适用于我的应用程序.
3. 是否有实际案例或理由将服务作为私有使用并在同一线程中运行?

推荐答案

应用程序主线程并不总是UI线程.例如，当Activity停止时，将调用onStop()，因此UI线程将从该Activity移走，并移至相同或不同应用程序中的另一个Activity.但是，这并不意味着该应用程序不再处于活动状态，它可以继续在后台运行，直到被操作系统或用户关闭.那么谁让它在后台运行呢?它是主线程，而不是UI线程.

Application main thread is not always the UI thread. For example, when Activity is stopped, the onStop() is invoked, hence the UI thread is taken away from that Activity and moved to another Activity within the same or a different application. However it doesn't mean the application is no longer active, it can continue working in the background until it is closed either by OS or by user. Then who keeps it running in the background? It is the main thread and not the UI thread.

什么是服务

在Android中，服务是可以执行的应用程序组件 UI线程在后台长时间运行的操作.经过 背景，则表示它没有用户界面.服务 默认情况下在调用组件的进程的主线程上运行 (因此可能会降低响应速度并引起ANR)，因此您 应该创建一个新的线程来执行长时间运行的操作.一种 服务也可以在完全不同的过程中运行.

In Android, a Service is an application component that can perform long-running operations in the background on the UI thread. By background, it means that it doesn’t have a user interface. A Service runs on the main thread of the calling Component’s process by default (and hence can degrade responsiveness and cause ANRs), hence you should create a new Thread to perform long running operations. A Service can also be made to run in a completely different process.

与活动组件不同，服务没有任何图形 接口.广播接收器也用于接收广播 消息(广播，多播，单播)并执行简短任务 而服务本应像流媒体一样进行冗长的处理 音乐，网络事务，文件I/O，与数据库交互等. 由活动之类的应用程序组件启动服务时 它在后台运行，即使用户切换也可以继续运行 转移到另一个应用程序或启动组件本身已被破坏

Unlike Activity components, Services do not have any graphical interfaces. Also Broadcast Receivers are for receiving broadcast messages (broadcast, multicast, unicast) and perform short tasks whereas Services are meant to do lengthy processing like streaming music, network transactions, file I/O, interact with databases, etc. When a Service is started by an application component like an Activity it runs in the background and keeps running even if the user switches to another application or the starting component is itself destroyed

为什么要使用服务

与其他后台进程相比，服务具有更高的优先级，并且 因此Android终止它的可能性较小.虽然可以 配置为在有足够的可用资源后重新启动 再次.您应该经历不同的过程及其 有关流程和流程的文档中的优先级/重要级别 线程.为他们分配与前台活动相同的优先级是 绝对有可能，在这种情况下，需要有一个可见的 通知处于活动状态(通常用于服务播放音乐).

Services are given higher priority than other Background processes and hence it’s less likely that Android will terminate it. Although it can be configured to restart once there is ample resources available again. You should go through the different processes and their priority/important level in the documentation on processes and threads. Assigning them the same priority as foreground activities is definitely possible in which case it’ll need to have a visible notification active (generally used for Services playing music).

如果您不想自己管理线程，请使用IntentService.否则，请使用AsyncTasks.

Use IntentService if you don't want to fiddle with managing threads on your own. Otherwise, use AsyncTasks.

请阅读这篇出色的文章，以详细了解，并且阅读此答案.

Please read this excellent article to understand more in detail and also read this answer.

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