Services 简介和分类

  A Service is an application component that can perform long-running operations in the background and does not provide a user interface. Another application component can start a service and it will continue to run in the background even if the user switches to another application. Additionally, a component can bind to a service to interact with it and even perform interprocess communication (IPC). For example, a service might handle network transactions, play music, perform file I/O, or interact with a content provider, all from the background.

  A service can essentially take two forms:

Started
  A service is "started" when an application component (such as an activity) starts it by calling startService(). Once started, a service can run in the background indefinitely, even if the component that started it is destroyed. Usually, a started service performs a single operation and does not return a result to the caller. For example, it might download or upload a file over the network. When the operation is done, the service should stop itself.
 started类型的service一但启动,一直在后台运行,直到自己停止或被停止,生命周期与启动者无关,不与启动者通信。
Bound
  A service is "bound" when an application component binds to it by calling bindService(). A bound service offers a client-server interface that allows components to interact with the service, send requests, get results, and even do so across processes with interprocess communication (IPC). A bound service runs only as long as another application component is bound to it. Multiple components can bind to the service at once, but when all of them unbind, the service is destroyed.
 Bound类型的service生命随绑定者存在,当有多个时,直到最后一个解绑才销毁。它是c-s中的s,通常与c通信。
  Although this documentation generally discusses these two types of services separately, your service can work both ways—it can be started (to run indefinitely) and also allow binding. It's simply a matter of whether you implement a couple callback methods: onStartCommand() to allow components to start it and onBind() to allow binding.
  Regardless of whether your application is started, bound, or both, any application component can use the service (even from a separate application), in the same way that any component can use an activity—by starting it with an Intent. However, you can declare the service as private, in the manifest file, and block access from other applications. This is discussed more in the section about Declaring the service in the manifest.
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.

The Basics 重要函数

  To create a service, you must create a subclass of Service (or one of its existing subclasses). In your implementation, you need to override some callback methods that handle key aspects of the service lifecycle and provide a mechanism for components to bind to the service, if appropriate. The most important callback methods you should override are:

  The system calls this method when another component, such as an activity, requests that the service be started, by calling startService(). Once this method executes, the service is started and can run in the background indefinitely. If you implement this, it is your responsibility to stop the service when its work is done, by calling stopSelf() or stopService(). (If you only want to provide binding, you don't need to implement this method.)
  The system calls this method when another component wants to bind with the service (such as to perform RPC), by calling bindService(). In your implementation of this method, you must provide an interface that clients use to communicate with the service, by returning an IBinder. You must always implement this method, but if you don't want to allow binding, then you should return null.
  The system calls this method when the service is first created, to perform one-time setup procedures (before it calls either onStartCommand() or onBind()). If the service is already running, this method is not called.
  The system calls this method when the service is no longer used and is being destroyed. Your service should implement this to clean up any resources such as threads, registered listeners, receivers, etc. This is the last call the service receives.

  If a component starts the service by calling startService() (which results in a call to onStartCommand()), then the service remains running until it stops itself with stopSelf() or another component stops it by calling stopService().

  If a component calls bindService() to create the service (and onStartCommand() is not called), then the service runs only as long as the component is bound to it. Once the service is unbound from all clients, the system destroys it.

  The Android system will force-stop a service only when memory is low and it must recover system resources for the activity that has user focus. If the service is bound to an activity that has user focus, then it's less likely to be killed, and if the service is declared to run in the foreground (discussed later), then it will almost never be killed. Otherwise, if the service was started and is long-running, then the system will lower its position in the list of background tasks over time and the service will become highly susceptible to killing—if your service is started, then you must design it to gracefully handle restarts by the system. If the system kills your service, it restarts it as soon as resources become available again (though this also depends on the value you return from onStartCommand(), as discussed later). For more information about when the system might destroy a service, see the Processes and Threading document.

  In the following sections, you'll see how you can create each type of service and how to use it from other application components.

Declaring a service in the manifest (声明一个service)

  Like activities (and other components), you must declare all services in your application's manifest file.

  To declare your service, add a <service> element as a child of the <application> element. For example:

 <manifest ... >
...
<application ... >
<service android:name=".ExampleService" />
...
</application>
</manifest>

  See the <service> element reference for more information about declaring your service in the manifest.

  There are other attributes you can include in the <service> element to define properties such as permissions required to start the service and the process in which the service should run. The android:name attribute is the only required attribute—it specifies the class name of the service. Once you publish your application, you should not change this name, because if you do, you risk breaking code due to dependence on explicit intents to start or bind the service (read the blog post, Things That Cannot Change).

  To ensure your app is secure, always use an explicit intent when starting or binding your Service and do not declare intent filters for the service. If it's critical that you allow for some amount of ambiguity as to which service starts, you can supply intent filters for your services and exclude the component name from the Intent, but you then must set the package for the intent with setPackage(), which provides sufficient disambiguation for the target service.

 两种类型的Service都要以精确型Intent启动。

  Additionally, you can ensure that your service is available to only your app by including the android:exported attribute and setting it to "false". This effectively stops other apps from starting your service, even when using an explicit intent.

Service官方教程(1)Started与Bound的区别、要实现的函数、声明service的更多相关文章

  1. Service官方教程(10)Bound Service的生命周期函数

    Managing the Lifecycle of a Bound Service When a service is unbound from all clients, the Android sy ...

  2. Service官方教程(6)Bound Services主要用来实现通信服务,以及3种实现通信的方案简介。

    1.Bound Services A bound service is the server in a client-server interface. A bound service allows ...

  3. Service官方教程(3)Bound Services

    Bound Services 1.In this document The Basics Creating a Bound Service Extending the Binder class Usi ...

  4. Service官方教程(8)Bound Service示例之2-跨进程使用Messenger

    Compared to AIDL When you need to perform IPC, using a Messenger for your interface is simpler than ...

  5. Service官方教程(9)绑定服务时的注意事项

    Binding to a Service Application components (clients) can bind to a service by calling bindService() ...

  6. Service官方教程(4)两种Service的生命周期函数

    Managing the Lifecycle of a Service The lifecycle of a service is much simpler than that of an activ ...

  7. Service官方教程(2)*IntentService与Service示例、onStartCommand()3个返回值的含义。

    1.Creating a Started Service A started service is one that another component starts by calling start ...

  8. linux下service+命令和直接去执行命令的区别,怎么自己建立一个service启动

    启动一些程序服务的时候,有时候直接去程序的bin目录下去执行命令,有时候利用service启动. 比如启动mysql服务时,大部分喜欢执行service mysqld start.当然也可以去mysq ...

  9. Service官方教程(11)Bound Service示例之2-AIDL 定义跨进程接口并通信

    Android Interface Definition Language (AIDL) 1.In this document Defining an AIDL Interface Create th ...

随机推荐

  1. vux tabbar 组件

    1.App.vue <!-- 入口文件 --> <template> <div id="app"> <!-- 视图层 --> < ...

  2. Java注释中的@deprecated与源代码中的@Deprecated

    用 @Deprecated注释的程序元素,不鼓励程序员使用这样的元素,通常是因为它很危险或存在更好的选择.在使用不被赞成的程序元素或在不被赞成的代码中执行重写时,编译器会发出警告. 其次,请注意标题, ...

  3. #Virtual hosts #Include conf/extra/httpd-vhosts.conf 开启就不能启动apache

    #Virtual hosts#Include conf/extra/httpd-vhosts.conf我只要把其中任何一个开启就是吧#去掉就启动不了apache.怎么回事error.log是这样的ht ...

  4. Struts2框架起源

    曾经也用过S2SH框架做过几个项目,都不是工作中的,学习WEB开发的时候接触的第一套框架也是S2SH,可是工作之后一直没实用到S2SH 框架进行开发. 感觉曾经用这个框架的时候根本没有深入去了解这个框 ...

  5. Hadoop之中的一个:Hadoop的安装部署

    说到Hadoop不得不说云计算了,我这里大概说说云计算的概念,事实上百度百科里都有,我仅仅是copy过来,好让我的这篇hadoop博客内容不显得那么单调.骨感.云计算近期今年炒的特别火,我也是个刚開始 ...

  6. Sublime Text 3设置吊炸天PHP开发环境

    @heiyeluren @created: 2016/5/31 @last modify: 2016/7/8 1. 下载安装Sublime Text 3 http://www.sublimetext. ...

  7. 【iOS系列】-UINavigationController的使用(Segue传递数据)

    [iOS系列]-UINavigationController的使用 UINavigationController是以以栈(先进后出)的形式保存子控制器, 常用属性: UINavigationItem有 ...

  8. button和submit区别

    type=button      就单纯是按钮功能 type=submit      是发送表单 但是对于从事WEB UI的人应该要注意到,使用submit来提高页面易用性: 使用submit后,页面 ...

  9. spring-boot快速搭建解析

    创建方式: 1.在File菜单里面选择 New > Project,然后选择Spring Initializr: 2.使用maven直接构建,添加依赖. 1 2 3 4 pom.xml:Mave ...

  10. python requests 调用restful api

    #!/usr/bin/python# -*- coding: utf-8 -*- import jsonimport requestsfrom urlparse import urljoin BASE ...