Android 上的“上下文"是什么? [英] What is 'Context' on Android?

问题描述

在 Android 编程中，Context 类到底是什么，它的用途是什么?

In Android programming, what exactly is a Context class and what is it used for?

我在开发者网站上阅读了相关内容，但我无法清楚地了解它.

I read about it on the developer site, but I am unable to understand it clearly.

推荐答案

简单地说:

顾名思义，它是应用程序/对象当前状态的上下文.它让新创建的对象了解发生了什么.通常，您调用它是为了获取有关程序另一部分(活动和程序包/应用程序)的信息.

As the name suggests, it's the context of the current state of the application/object. It lets newly-created objects understand what has been going on. Typically you call it to get information regarding another part of your program (activity and package/application).

您可以通过调用getApplicationContext()、getContext()、getBaseContext() 或this 来获取上下文>(当在从 Context 扩展的类中时，例如 Application、Activity、Service 和 IntentService 类).

You can get the context by invoking getApplicationContext(), getContext(), getBaseContext() or this (when in a class that extends from Context, such as the Application, Activity, Service and IntentService classes).

上下文的典型用途:

• 创建新对象:创建新的视图、适配器、侦听器:

• Creating new objects: Creating new views, adapters, listeners:

 TextView tv = new TextView(getContext());
 ListAdapter adapter = new SimpleCursorAdapter(getApplicationContext(), ...);

访问标准公共资源:LAYOUT_INFLATER_SERVICE、SharedPreferences 等服务:

Accessing standard common resources: Services like LAYOUT_INFLATER_SERVICE, SharedPreferences:

 context.getSystemService(LAYOUT_INFLATER_SERVICE)
 getApplicationContext().getSharedPreferences(*name*, *mode*);

隐式访问组件:关于内容提供者、广播、意图

Accessing components implicitly: Regarding content providers, broadcasts, intent

 getApplicationContext().getContentResolver().query(uri, ...);

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