Application概念理解
官方释义:
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.There is normally no need to subclass Application. In most situation, static singletons can provide the same functionality in a more modular way. If your singleton needs a global context (for example to register broadcast receivers), the function to retrieve
it can be given a Context which internally uses Context.getApplicationContext() when first constructing the singleton.个人翻译:
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>标签中指定名称进行自己的实现,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。
子类Application通常是没有必要的。大多数情况下,静态的单例可以通过更加模块化的方式提供相同的功能,如果你的单例需要一个全局的Context(例如注册一个广播接收器),当第一次构建单例时,程序内部使用Context.getApplication()方法可以返回一个Context(上下文)。
个人理解:
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,直接在Application中去实现。只需要调用Context的getApplicationContext或者Activity的getApplication方法来就可以获得一个Application对象。
接下来通过例子来看一下具体用法:
GlobalParameterApplication.java
package com.dt5000.ischool.util; import android.app.Application; import com.dt5000.ischool.bean.User; /** * @author: duanyr * @创建时间: 2012-11-14 上午10:50:45 * * 类说明:全局参数类 */ public class GlobalParameterApplication extends Application { private User user; public User getUser() { return user; } public void setUser(User user) { this.user = user; } }
package com.dt5000.ischool.activity; import android.app.Activity; import com.dt5000.ischool.bean.User; import com.dt5000.ischool.util.GlobalParameterApplication; public class UserLoginActivity extends Activity { @Override protected void onStart() { // TODO Auto-generated method stub User user = new User(); user.setUserName("example"); GlobalParameterApplication gpa = (GlobalParameterApplication) getApplicationContext(); gpa.setUser(user);// 将User信息放入到Application gpa.getUser();//取出User信息 super.onStart(); } }
AndroidManifest.xml
<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.dt5000.ischool.activity" android:versionCode="1" android:versionName="1.0" > <uses-sdk android:minSdkVersion="8" android:maxSdkVersion="15" android:targetSdkVersion="8" /> <application android:name="com.dt5000.ischool.util.GlobalParameterApplication" android:icon="@drawable/ic_launcher" android:label="@string/app_name" android:theme="@android:style/Theme.NoTitleBar" > <activity android:name=".WelcomeActivity" android:label="@string/title_activity_welcome" > <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> </manifest>
注意:不用新建<application />,在原有基础上添加内容:android:name=".your_App_Name"