http://blog.csdn.net/duer8797/article/details/6990965
在代码中经常看到application这个类,一直不知道这个是干什么用的,今天刚好有点时间,所以进行了详细的学习。
一.先对它的整体概念解释:
在android源码中对他的描述是;
* Base class for those who need to maintain global application state. You can
* provide your own implementation by specifying its name in your
* AndroidManifest.xml's <application> tag, which will cause that class
* to be instantiated for you when the process for your application/package is
* created.
SDK中的描述:Application类是为了那些需要保存全局变量设计的基本类,你可以在AndroidManifest.xml的<application>标签中进行自己的实现,这样的结果是:当你的 application或者包被建立的时候将引起那个类被建立。
理解:就是说application是用来保存全局变量的,并且是在package创建的时候就跟着存在了。所以当我们需要创建全局变量的时候,不需 要再像j2se那样需要创建public权限的static变量,而直接在application中去实现。只需要调用Context的getApplicationContext或者Activity的getApplication方法来获得一个application对象,再做出相应 的处理。
例如Launcher模块中;它自己就写了个application,在AndroidManifest.xml中将它进行了设置:
<application
android:name="com.android.launcher2.LauncherApplication"
对于他的设置可以参考这个模块。
二.里面的方法进行说明:
onCreate();
/**
* Called when the application is starting, before any other application
* objects have been created. Implementations should be as quick as
* possible (for example using lazy initialization of state) since the time
* spent in this function directly impacts the performance of starting the
* first activity, service, or receiver in a process.
* If you override this method, be sure to call super.onCreate().
*/
这个函数是当我们的应用开始之时就被调用了,比应用中的其他对象创建的早,这个实现尽可能的快一点,因为这个时间直接影响到我们第一个activity/service
/receiver。如果你要重写这个方法必须调用super.onCreate().
onTerminate():
/**
* This method is for use in emulated process environments. It will
* never be called on a production Android device, where processes are
* removed by simply killing them; no user code (including this callback)
* is executed when doing so.
*/
这个函数是模拟一个过程环境,在真机中永远也不会被调用。
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