Android 实例解说Application类

版本：1.0

日期：2014.3.28

何为Application，有何用途？Google官方文档是这样说的：维护全局应用程序的状态，使用的时候继承于它创建一个子类即可，同时在AndroidManifest.xml文件的<application> 标签的name属性制定它的名字，也就是子类名称。当应用程序的包被创建的时候这个类就会被实例化，而且它的生命周期和应用程序是一样的。不过Google在下面的提示中也说道大多数情况下不需要使用这个类，因为如果应用程序使用了单例模式的话，效果和Application提供的事一样的，而且也更加容易控制、规范。

关于Application类有以下公开方法：

其中最常用的就是onCreaet()、onTerminate()以及onLowMemory()方法，onCreaet()它会在这个类实例化的时候调用（这个地方需要十分注意，它只会在程序第一次启动的时候调用，不是每次都调用，因为Application类会在创建包的时候初始化），onTerminate()会在app关闭的时候调用，onLowMemory()是在内存过低的情况下调用的。那onTerminate()是干什么用的呢？网上介绍说是在程序终结的时候调用，从下面的实例中也是这样用的。不过在Google的开发文档以及很多书籍对这个类的用法很少提及，但实际开发情况是如何的呢。不妨反编译几个常用的app一看究竟，因为涉及到一些因素就不方便说是哪个app，以代号表明。

1、app_1

先把代码贴出来，因为这个app的Application的实现比较简单，就先拿出来说。

import android.annotation.TargetApi;
import android.app.Application;
import android.content.Context;
import android.os.Build.VERSION;
import com.nostra13.universalimageloader.cache.disc.naming.Md5FileNameGenerator;
import com.nostra13.universalimageloader.core.ImageLoader;
import com.nostra13.universalimageloader.core.ImageLoaderConfiguration;
import com.nostra13.universalimageloader.core.ImageLoaderConfiguration.Builder;
import com.nostra13.universalimageloader.core.assist.QueueProcessingType;
import java.io.PrintStream;
import org.apache.http.HttpVersion;
import org.apache.http.client.HttpClient;
import org.apache.http.conn.ClientConnectionManager;
import org.apache.http.conn.scheme.PlainSocketFactory;
import org.apache.http.conn.scheme.Scheme;
import org.apache.http.conn.scheme.SchemeRegistry;
import org.apache.http.conn.ssl.SSLSocketFactory;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.impl.conn.tsccm.ThreadSafeClientConnManager;
import org.apache.http.params.BasicHttpParams;
import org.apache.http.params.HttpConnectionParams;
import org.apache.http.params.HttpProtocolParams;public class MyApplicationextends Application
{private HttpClient httpClient;public boolean isLogin = false;private HttpClient createHttpClient(){BasicHttpParams localBasicHttpParams = new BasicHttpParams();HttpProtocolParams.setVersion(localBasicHttpParams, HttpVersion.HTTP_1_1);HttpProtocolParams.setContentCharset(localBasicHttpParams, "ISO-8859-1");HttpProtocolParams.setUseExpectContinue(localBasicHttpParams, true);HttpConnectionParams.setConnectionTimeout(localBasicHttpParams, 20000);HttpConnectionParams.setSoTimeout(localBasicHttpParams, 20000);HttpConnectionParams.setSocketBufferSize(localBasicHttpParams, 8192);SchemeRegistry localSchemeRegistry = new SchemeRegistry();localSchemeRegistry.register(new Scheme("http", PlainSocketFactory.getSocketFactory(), 80));localSchemeRegistry.register(new Scheme("https", SSLSocketFactory.getSocketFactory(), 443));return new DefaultHttpClient(new ThreadSafeClientConnManager(localBasicHttpParams, localSchemeRegistry), localBasicHttpParams);}public static void initImageLoader(Context paramContext){ImageLoaderConfiguration localImageLoaderConfiguration = new ImageLoaderConfiguration.Builder(paramContext).threadPriority(3).denyCacheImageMultipleSizesInMemory().discCacheFileNameGenerator(new Md5FileNameGenerator()).tasksProcessingOrder(QueueProcessingType.LIFO).writeDebugLogs().build();ImageLoader.getInstance().init(localImageLoaderConfiguration);}private void shutdownHttpClient(){if ((this.httpClient != null) && (this.httpClient.getConnectionManager() != null)) {this.httpClient.getConnectionManager().shutdown();}}public HttpClient getHttpClient(){return this.httpClient;}@TargetApi(9)public void onCreate(){super.onCreate();this.httpClient = createHttpClient();System.out.println(Build.VERSION.SDK_INT);initImageLoader(getApplicationContext());}public void onLowMemory(){super.onLowMemory();shutdownHttpClient();}public void onTerminate(){super.onTerminate();shutdownHttpClient();}public static class Config{public static final boolean DEVELOPER_MODE;}
}

从import导入的包就可以看出来，在这个类里面使用了强大的universalimageloader异步加载图片以及使用的apache的HttpClient。然后整体看一下这个类，发现它不仅重载了onCreate()方法，还重载了onLowMemory()以及onTerminate()方法。onLowMemory()顾名思义就是在Android系统内存低的情况下调用的，可以在这个方法里面做一下释放内存的功能。

那就从onCreate()方法开始，里面代码如下：

  this.httpClient = createHttpClient();System.out.println(Build.VERSION.SDK_INT);initImageLoader(getApplicationContext());

第一个方法，创建httpClient的对象，至于方法的具体细节就不介绍了，不是本文讨论重点，下同。第二个方法就是初始化universalimageloader了。总体来说这个app的Application的实现还是比较简单的，也比较容易理解。接下来介绍一个稍微复杂一点的。

2、app_2

import android.app.Application;
import android.content.pm.ApplicationInfo;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.os.Environment;
import android.widget.Toast;
import com.baidu.mapapi.BMapManager;
import com.baidu.mapapi.MKGeneralListener;
import com.baidu.mapapi.MKLocationManager;
import java.io.File;public class Appextends Application
{public static App app;public static boolean hideOtherExchanges = false;public static boolean hideUpdateNotice = false;public BMapManager mBMapMan = null;public String mStrKey = "4BFEB7A7F3E7CD4B0FBAE61BABD11F1E11D7EAC8";public static void delete(File paramFile){if (paramFile.isFile()) {paramFile.delete();}while (!paramFile.isDirectory()) {return;}File[] arrayOfFile = paramFile.listFiles();if ((arrayOfFile == null) || (arrayOfFile.length == 0)){paramFile.delete();return;}for (int i = 0;; i++){if (i >= arrayOfFile.length){paramFile.delete();return;}delete(arrayOfFile[i]);}}public boolean init(){this.mBMapMan = new BMapManager(this);return this.mBMapMan.init(this.mStrKey, new MyGeneralListener());}public void onCreate(){app = this;if (init()) {this.mBMapMan.getLocationManager().setNotifyInternal(10, 5);}super.onCreate();try{localBundle = getPackageManager().getApplicationInfo(getPackageName(), 128).metaData;str2 = localBundle.getString("UMENG_CHANNEL");arrayOfString1 = localBundle.getString("HIDE_OTHER_EXCHANGE_APK_CHANNEL").split(",");i = 0;}catch (Exception localException1){for (;;){Bundle localBundle;String str2;String[] arrayOfString1;int i;String[] arrayOfString2;int j;Logger.w(localException1);continue;i++;continue;label303:if (arrayOfString2[j].equals(str2)) {hideUpdateNotice = true;} else {j++;}}}if (i >= arrayOfString1.length) {}for (;;){arrayOfString2 = localBundle.getString("HIDE_DOUGUO_UPDATE_NOTICE").split(",");j = 0;int k = arrayOfString2.length;if (j < k) {break label303;}WeiboHelper.setConfig(app);RenrenHelper.setConfig(app);DouguoWebAPI.setConfig(app);Logger.setConfig(app);Thread.setDefaultUncaughtExceptionHandler(new ExceptionHandler(getApplicationContext()));try{String str1 = Environment.getExternalStorageDirectory().getAbsolutePath() + "/douguo/" + getPackageName();File localFile1 = new File(str1);File localFile2 = localFile1.getParentFile();if (!localFile2.exists()) {localFile2.mkdir();}if (!localFile1.exists()) {localFile1.mkdir();}File localFile3 = new File(str1 + "/.nomedia");if (!localFile3.exists()) {localFile3.createNewFile();}return;}catch (Exception localException2){Logger.w(localException2);}if (!arrayOfString1[i].equals(str2)) {break;}hideOtherExchanges = true;}}public void onLowMemory(){super.onLowMemory();Logger.e("!!!!!!!!!!!!!!onLowMemory!!!!!!!!!!!!");}public void onTerminate(){if (this.mBMapMan != null){this.mBMapMan.destroy();this.mBMapMan = null;}super.onTerminate();new Thread(){public void run(){App.delete(new File(Environment.getExternalStorageDirectory() + "/douguo/yummyDiary/"));}}.start();}static class MyGeneralListenerimplements MKGeneralListener{public void onGetNetworkState(int paramInt){Toast.makeText(App.app.getApplicationContext(), "您的网络出错啦！", 1).show();}public void onGetPermissionState(int paramInt) {}}
}

这个类有两个自定义的方法，一个是delete(File paramFile)，用于删除指定文件，一个是init()，用于初始化百度地图以及网络连接。进入onCreate()方法，首选是给变量app实例化。接着调用init()方法进行判断，如果在init()方法返回true，说明有网络连接正常并且已经初始化完毕百度地图，之后会不断发送tNotify通知。然后进入try catch方法里面，由于反编译的问题，有些语句反编译完毕后就是现在这个样子。至于如何解读，以后会介绍，现在不是重点。看一下，在try里面是初始化了友盟的一些东西，然后再catch里面声明了一些变量，并且根据某些条件创建或者删除指定的文件。最后就是onTerminate()方法，可以看到在这个方法里面它销毁了百度地图、删除了一些程序的文件等。

3、app_3

import android.app.ActivityManager;
import android.app.ActivityManager.RunningAppProcessInfo;
import android.app.Application;
import android.content.Context;
import android.os.Process;
import com.baidu.android.silentupdate.SilentManager;
import java.util.Iterator;
import java.util.List;public class FrontiaApplicationextends Application
{private static final String a = "MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCYAFbG0oYmKgh6o7BhZIHf1njBpZXqyWBnYz2ip3Wp+s97OeA/pTe8xebuGJHwq4xbsGQrJWepIbUVrdjm6JRmdvuJhar7/hC/UNnUkJgYdYl10OZKlvcFFgK3V7XGBPplXldDnhbgscna3JG8U3025WSxZCP5vy/8cfxsEoVx5QIDAQAB";public static void initFrontiaApplication(Context paramContext){SilentManager.setKey("MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQCYAFbG0oYmKgh6o7BhZIHf1njBpZXqyWBnYz2ip3Wp+s97OeA/pTe8xebuGJHwq4xbsGQrJWepIbUVrdjm6JRmdvuJhar7/hC/UNnUkJgYdYl10OZKlvcFFgK3V7XGBPplXldDnhbgscna3JG8U3025WSxZCP5vy/8cfxsEoVx5QIDAQAB");SilentManager.enableRSA(false);SilentManager.loadLib(paramContext.getApplicationContext(), "frontia_plugin", "plugin-deploy.jar");}public void onCreate(){super.onCreate();ActivityManager localActivityManager = (ActivityManager)getSystemService("activity");int i = Process.myPid();Iterator localIterator = localActivityManager.getRunningAppProcesses().iterator();while (localIterator.hasNext()){ActivityManager.RunningAppProcessInfo localRunningAppProcessInfo = (ActivityManager.RunningAppProcessInfo)localIterator.next();if ((localRunningAppProcessInfo.pid == i) && (!localRunningAppProcessInfo.processName.endsWith(getPackageName()))) {initFrontiaApplication(getApplicationContext());}}}
}import android.content.Context;
import com.baidu.frontia.FrontiaApplication;
import com.nostra13.universalimageloader.cache.disc.naming.Md5FileNameGenerator;
import com.nostra13.universalimageloader.core.ImageLoader;
import com.nostra13.universalimageloader.core.ImageLoaderConfiguration;
import com.nostra13.universalimageloader.core.ImageLoaderConfiguration.Builder;
import com.nostra13.universalimageloader.core.assist.QueueProcessingType;public class UILApplicationextends FrontiaApplication
{public static void initImageLoader(Context paramContext){ImageLoaderConfiguration localImageLoaderConfiguration = new ImageLoaderConfiguration.Builder(paramContext).threadPriority(3).denyCacheImageMultipleSizesInMemory().discCacheFileNameGenerator(new Md5FileNameGenerator()).tasksProcessingOrder(QueueProcessingType.LIFO).build();ImageLoader.getInstance().init(localImageLoaderConfiguration);}public void onCreate(){com.nostra13.universalimageloader.utils.StorageUtils.basePath = "Meishi";com.nostra13.universalimageloader.utils.StorageUtils.childPath = "Temp";com.nostra13.universalimageloader.utils.StorageUtils.childImgName = "imgs";super.onCreate();CrashHandler.getInstance().init(this);initImageLoader(getApplicationContext());}
}

这个app的Application的实现比较特殊一点，使用了两个类，在第一个类的onCreate()方法里面主要是先是获取所有的进程，然后迭代进行判断，如果满足条件则调用initFrontiaApplication()方法用来设置key。第二个类则用于初始化universalimageloader。其实觉得没有必要分开来操作，写在一个Application类里面即可。

4、app_4

import android.app.Application;
import android.graphics.Bitmap.Config;
import android.text.TextUtils;
import android.webkit.CookieManager;
import android.webkit.CookieSyncManager;
import cn.jpush.android.api.BasicPushNotificationBuilder;
import cn.jpush.android.api.JPushInterface;
import com.baidu.location.BDLocation;
import com.baidu.location.LocationClient;
import com.baidu.location.LocationClientOption;
import com.baidu.mapapi.BMapManager;
import com.baidu.mapapi.MKGeneralListener;
import com.nostra13.universalimageloader.cache.memory.impl.WeakMemoryCache;
import com.nostra13.universalimageloader.core.DisplayImageOptions;
import com.nostra13.universalimageloader.core.DisplayImageOptions.Builder;
import com.nostra13.universalimageloader.core.ImageLoader;
import com.nostra13.universalimageloader.core.ImageLoaderConfiguration;
import com.nostra13.universalimageloader.core.ImageLoaderConfiguration.Builder;
import com.nostra13.universalimageloader.core.assist.ImageScaleType;
import com.nostra13.universalimageloader.core.display.RoundedBitmapDisplayer;
import java.util.Calendar;
import java.util.Date;public class AzkAppextends Application
{public static final String BASEURL = Api.BASE_URL;public static DisplayImageOptions avatarOptions;public static DisplayImageOptions defaultOptions;private static AzkApp instance;private static boolean jpushInitied;public static DisplayImageOptions noStubOptions;private final String COOKIEURL = "http://aimeiwei.me";public BDLocation bdLocation;private CookieManager cookieManager;private CookieSyncManager cookieSyncManager;public BMapManager mBMapMan;public LocationClient mLocationClient;public int mapCount;private String nickname = "";private String password = "";private String username = "";private String getBaiduKey(){return AzkHelper.getMetaData(getApplicationContext(), "BAIDU_KEY");}public static AzkApp getInstance(){return instance;}private void initCookieManager(){this.cookieSyncManager = CookieSyncManager.createInstance(this);this.cookieManager = CookieManager.getInstance();this.cookieManager.setAcceptCookie(true);if (isLogin()){String str = this.cookieManager.getCookie("http://aimeiwei.me");if ((str == null) || (!str.contains("username")) || (!str.contains("password"))){AzkHelper.showLog("初始化cookie");setCookie(this.username, this.password);}}showCookie();}private void initHttp(){AzkHelper.showLog("httpClient初始化");Http.initHttp(AzkHelper.sAzkUserAgent);Http.setBaseUrl(Api.API_URL);if ((!TextUtils.isEmpty(this.username)) && (!TextUtils.isEmpty(this.password))) {Http.setUser(this.username, this.password);}}private void initImageLoader(){AzkHelper.showLog("ImageLoader图片加载器初始化");long l1 = Runtime.getRuntime().maxMemory();long l2 = l1 / 1024L / 1024L;AzkHelper.showLog("maxHeap: " + l2);int i = (int)l1 / 4;DisplayImageOptions.Builder localBuilder1 = new DisplayImageOptions.Builder();DisplayImageOptions.Builder localBuilder2 = localBuilder1.showImageOnLoading(2130837835);Bitmap.Config localConfig;ImageScaleType localImageScaleType;label103:int j;label188:ImageLoaderConfiguration.Builder localBuilder6;if (l2 >= 256L){localConfig = Bitmap.Config.ARGB_8888;DisplayImageOptions.Builder localBuilder3 = localBuilder2.bitmapConfig(localConfig);if (l2 < 256L) {break label283;}localImageScaleType = ImageScaleType.IN_SAMPLE_POWER_OF_2;localBuilder3.imageScaleType(localImageScaleType).cacheInMemory(true).cacheOnDisc(true);defaultOptions = localBuilder1.build();DisplayImageOptions.Builder localBuilder4 = new DisplayImageOptions.Builder();localBuilder4.cacheInMemory(true).cacheOnDisc(true);noStubOptions = localBuilder4.build();ImageLoaderConfiguration.Builder localBuilder5 = new ImageLoaderConfiguration.Builder(getApplicationContext()).memoryCacheExtraOptions(Constants.IMAGE_SIZE, Constants.IMAGE_SIZE);if (l2 < 256L) {break label291;}j = 1;localBuilder6 = localBuilder5.threadPriority(5 - j);if (l2 < 256L) {break label297;}}label283:label291:label297:for (int k = 3;; k = 2){ImageLoaderConfiguration localImageLoaderConfiguration = localBuilder6.threadPoolSize(k).memoryCacheSize(i).memoryCache(new WeakMemoryCache()).denyCacheImageMultipleSizesInMemory().defaultDisplayImageOptions(defaultOptions).build();ImageLoader.getInstance().init(localImageLoaderConfiguration);avatarOptions = localBuilder1.displayer(new RoundedBitmapDisplayer(8)).build();return;localConfig = Bitmap.Config.RGB_565;break;localImageScaleType = ImageScaleType.IN_SAMPLE_INT;break label103;j = 2;break label188;}}private void removeCookie(){this.cookieManager.removeSessionCookie();this.cookieManager.removeAllCookie();this.cookieSyncManager.sync();}private void setCookie(String paramString1, String paramString2){Calendar localCalendar = Calendar.getInstance();localCalendar.set(2025, 11, 29);String str = localCalendar.getTime().toString();this.cookieManager.setCookie("http://aimeiwei.me", "username=" + paramString1 + "; path=/; expires=" + str);this.cookieManager.setCookie("http://aimeiwei.me", "password=" + paramString2 + "; path=/; expires=" + str);this.cookieSyncManager.sync();showCookie();}private void setJpushAlias(){AzkHelper.showLog("jpush", "username: " + this.username);JPushInterface.setAliasAndTags(this, this.username, null);}private void showCookie(){String str = this.cookieManager.getCookie("http://aimeiwei.me");AzkHelper.showLog("cookie:" + str);}public String getNickname(){return this.nickname;}public String getPassword(){return this.password;}public String getUsername(){return this.username;}public void initBMapManager(){if (this.mBMapMan == null){this.mBMapMan = new BMapManager(this);String str = getBaiduKey();AzkHelper.showLog("初始化BMapManager, BAIDU_KEY: " + str);this.mBMapMan.init(str, new MKGeneralListener(){public void onGetNetworkState(int paramAnonymousInt){if (paramAnonymousInt == 2) {AzkHelper.showErrorLog("您的网络出错啦！");}}public void onGetPermissionState(int paramAnonymousInt){if (paramAnonymousInt == 300) {AzkHelper.showLog("请输入正确的百度授权Key");}}});}}public void initJpush(){if (jpushInitied) {return;}AzkHelper.showLog("极光推送初始化");AzkHelper.showLog("jpush", "极光推送初始化");JPushInterface.init(this);BasicPushNotificationBuilder localBasicPushNotificationBuilder = new BasicPushNotificationBuilder(this);localBasicPushNotificationBuilder.statusBarDrawable = 2130837777;JPushInterface.setPushNotificationBuilder(Integer.valueOf(1), localBasicPushNotificationBuilder);if (!TextUtils.isEmpty(this.username)) {setJpushAlias();}jpushInitied = true;}public void initMap(){AzkHelper.showLog("百度地图初始化");this.mLocationClient = new LocationClient(this);LocationClientOption localLocationClientOption = new LocationClientOption();localLocationClientOption.setProdName(getString(2131296262));localLocationClientOption.setOpenGps(true);localLocationClientOption.setPriority(2);localLocationClientOption.setAddrType("all");localLocationClientOption.setCoorType("gcj02");this.mLocationClient.setLocOption(localLocationClientOption);this.mLocationClient.setAK(getBaiduKey());initBMapManager();}public boolean isLogin(){boolean bool = true;if ((TextUtils.isEmpty(this.username)) || (TextUtils.isEmpty(this.password))) {bool = false;}return bool;}public boolean isYourself(User paramUser){if ((TextUtils.isEmpty(this.username)) || (paramUser == null)) {return false;}return this.username.equals(paramUser.getId());}public boolean isYourself(UserNew paramUserNew){if ((TextUtils.isEmpty(this.username)) || (paramUserNew == null)) {return false;}return this.username.equals(paramUserNew.getId());}public void onCreate(){AzkHelper.showLog("Application Aimeiwei onCreate");super.onCreate();instance = this;AzkHelper.prepareUserAgent(this);this.username = AzkHelper.getStringPref(this, "username");this.password = AzkHelper.getStringPref(this, "password");this.nickname = AzkHelper.getStringPref(this, "nickname");AzkHelper.showLog("BuildConfig.DEBUG: false");AzkHelper.closeLog();initHttp();initImageLoader();initJpush();initMap();initCookieManager();}public void onLowMemory(){AzkHelper.showLog("onLowMemory");super.onLowMemory();}public void onTerminate(){instance = null;if (this.mBMapMan != null){this.mBMapMan.destroy();this.mBMapMan = null;}super.onTerminate();}public void removeUser(){Http.clearUser();AzkHelper.removePref(this, "username");AzkHelper.removePref(this, "password");AzkHelper.removePref(this, "nickname");this.username = "";this.password = "";this.nickname = "";AccessTokenKeeper.clear(getApplicationContext());removeCookie();}public void removeUser2(){Http.clearUser();AzkHelper.removePref(this, "username");AzkHelper.removePref(this, "password");AzkHelper.removePref(this, "nickname");this.password = "";this.nickname = "";AccessTokenKeeper.clear(getApplicationContext());AccessTokenKeeperForQQ.clear(getApplicationContext());removeCookie();}public void setNickname(String paramString){AzkHelper.setStringPref(this, "nickname", paramString);this.nickname = paramString;}public void setPassword(String paramString){AzkHelper.setStringPref(this, "password", paramString);this.password = paramString;}public void setUser(String paramString1, String paramString2){setUserName(paramString1);setPassword(paramString2);Http.setUser(paramString1, paramString2);}public void setUser(String paramString1, String paramString2, String paramString3){setNickname(paramString3);setUser(paramString1, paramString2);setCookie(paramString1, paramString2);}public void setUserName(String paramString){AzkHelper.setStringPref(this, "username", paramString);this.username = paramString;setJpushAlias();}
}

这个app的实现相对来说还是比较复杂的，但是无非就是初始化一些信息。从import导包可以看到，使用了极光推送、百度地图以及universalimageloader，所以按照之前的分析经验之后一定会在onCreate()方法里面去初始化这些功能的。看一下onCreate()方法：

  public void onCreate(){AzkHelper.showLog("Application Aimeiwei onCreate");super.onCreate();instance = this;AzkHelper.prepareUserAgent(this);this.username = AzkHelper.getStringPref(this, "username");this.password = AzkHelper.getStringPref(this, "password");this.nickname = AzkHelper.getStringPref(this, "nickname");AzkHelper.showLog("BuildConfig.DEBUG: false");AzkHelper.closeLog();initHttp();initImageLoader();initJpush();initMap();initCookieManager();}

很清晰明了，从方法名称也可以看出来，就是初始化各种功能。至于具体方法的实现，不多做介绍，感兴趣可以自己去研究。

最后总结一下，上面例举了四个市场上的app程序的Application类的实现。从中可以发现，在Application类的实现类中，无非就是做一些初始化程序数据、检查运行环境、销毁数据等。

1、初始化程序数据：

常用的初始化的手段有创建程序所需要的目录，设置开发平台的key，初始化地图信息，初始化http或者其他和网络有关的东西，初始化推送等等。

2、检查运行环境

比如检查是否存在sd卡、判断网络连接状况、检查内存等等。

3、销毁数据

就是在onTerminate()方法里面销毁之前使用到的一些东西。说到onTerminate()这个方法，在官方文档中是这样说的，

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.

它是在模拟环境下调用的，在真机中永远不会被调用。那为什么那么多app的Application类都用到这个方法呢？下面写一个demo测试一下，看结果如何。

首先在真机测试，代码：

import android.app.Application;public class APP extends Application{@Overridepublic void onCreate() {// TODO Auto-generated method stubsuper.onCreate();System. out.println("onCreate()" );}@Overridepublic void onLowMemory() {// TODO Auto-generated method stubsuper.onLowMemory();System. out.println("onCreate()" );}@Overridepublic void onTerminate() {// TODO Auto-generated method stubsuper.onTerminate();System. out.println("onCreate()" );}}

结果：

打开程序的时候调用了ocCreate()方法，这个没有问题，下面退出程序看看。我直接按返回家退出，发现并没有调用onTerminate()方法。接下来使用模拟器看看结果如何：

运行程序，发现调用了ocCreate()方法，

退出程序看看，发现也没有调用。所以感觉onTerminate()这个方法还是不要使用为好，官方既然说了不会再真机中调用，那么应该不会有错。所以在很多app里面使用到了这个方法，有点不明觉厉，明白的朋友可以交流一下。

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android application 全局变量空指针,Android编程之Application设置全局变量及传值用法实例分析...
本文实例讲述了Android编程之Application设置全局变量及传值用法.分享给大家供大家参考,具体如下: /** * 重写Application,主要重写里面的onCreate方法,就是创建的 ...
Android学习笔记（三）Application类简介
每次运行APP时,Application类都保持实例化状态.与Activity不同,配置改变不会导致应用程序重启.通过继承Application类,可以完成一下3项工作: · 对Android运行时广 ...
android获得application类对象,android之Application类介绍
Application类 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. 当我们需要创建全局变量的时候,而直接在application中去实现. 只需要调用 ...
android 快速开发常用工具类,实例详解Android快速开发工具类总结
一.日志工具类 Log.java public class L { private L() { /* 不可被实例化 */ throw new UnsupportedOperationException ...
Android中用Application类实现全局变量
在Java中如果要使用全局变量,一般定义public static类型的变量.但是这种方法不符合Android的框架架构,Android中要使用Application context. Applica ...
Android中Application类用法
Application类 Application和Activity,Service一样是Android框架的一个系统组件,当Android程序启动时系统会创建一个Application对象,用来存储系 ...
Android application类
什么是application类? application是维护应用全局状态的基类,应用进程启动时android系统会创建application类并调用类的onCreate()函数,applicatio ...

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