Android中Context简介

Android中Context简介

Context字面意思是上下文，位于framework package的android.content.Context中，其实该类为LONG型，类似Win32中的Handle句柄。很多方法需要通过 Context才能识别调用者的实例：比如说Toast的第一个参数就是Context，一般在Activity中我们直接用this代替，代表调用者的实例为Activity，而到了一个button的onClick(View view)等方法时，我们用this时就会报错，所以我们可能使用ActivityName.this来解决，主要原因是因为实现Context的类主要有Android特有的几个模型，Activity以及Service。
Context提供了关于应用环境全局信息的接口。它是一个抽象类，它的执行被Android系统所提供。它允许获取以应用为特征的资源和类型。同时启动应用级的操作，如启动Activity，broadcasting和接收intents。
下面介绍Context的一些get方法，通过这些get方法可以获取应用环境全局信息：
1.public abstract
Context getApplicationContext ()
Return the context of the single, global
Application object of the current process.
2.public abstract
ApplicationInfo getApplicationInfo ()
Return the full application info for this
context's package.
3.public abstract
ContentResolver getContentResolver ()
Return a ContentResolver instance for your
application's package.
4.public abstract
PackageManager getPackageManager ()
Return PackageManager instance to find
global package information.
5.public abstract
String getPackageName ()
Return the name of this application's
package.
6.public abstract
Resources getResources ()
Return a Resources instance for your
application's package.
7.public abstract SharedPreferences getSharedPreferences (String
name, int mode)
Retrieve and hold the contents of the
preferences file 'name', returning a SharedPreferences through which you can
retrieve and modify its values. Only one instance of the SharedPreferences object
is returned to any callers for the same name, meaning they will see each
other's edits as soon as they are made.
8.public final
String getString (int resId)
Return a localized string from the
application's package's default string table.
9.public abstract
Object getSystemService (String name)
Return the handle to a system-level
service by name. The class of the returned object varies by the requested name.
Currently available names are:
还有很多有用的方法，具体不一一列举。详情请参考文档，反正Context很有用。