Android源代码之DeskClockProxy/Delegate Application 框架应用 _Application

青春须早为，岂能长少年。这篇文章主要讲述Android源代码之DeskClockProxy/Delegate Application 框架应用相关的知识，希望能为你提供帮助。
一.概述当项目有加壳子,插件化或热修复等需求的时候,能够使用Proxy/Delegate Application框架的方式,在正常的模式中,一个程序一般仅仅有一个Application入口,而Proxy/Delegate模式中须要有两个Application,原程序的Application改为Delegate Application,再新加一个Proxy Application,由Proxy Application 提供一系列的个性化定制,再将所有的context和context相关的引用所有转化为Delegate Application的实例,让外界包含Delegate Application自身都以为该App的Application入口就是Delegate Application.
二.实例 1.Proxy/Delegate 之前这里就在android 4.4原生的DeskClock程序上应用Proxy/Delegate框架为演示样例原生的DeskClock程序没有自己定义Application,这里先定义一个,并print该程序眼下ApplicationContext的名字(在DeskClock中使用的Log是自己定义的)

/** * Created by jesse on 15-7-17. */ public class MyApplication extends Application{ private final String TAG = MyApplication.class.getSimpleName(); @Override public void onCreate() { super.onCreate(); Log.i(TAG + " , onCreate " + this.getApplicationContext().getClass().getSimpleName()); } }

而且在DeskClock的入口Activity,DeskClock处也print出该程序眼下ApplicationContext的名字用于兴许Proxy后的对照. Application的Manifest配置是

< application android:name=" cn.jesse.MyApplication" android:label=" @string/app_label" android:icon=" @mipmap/ic_launcher_alarmclock" android:requiredForAllUsers=" true" android:supportsRtl=" true" >

过滤后的执行Log: 简单的流程就是先启动自己定义MyApplication 之后再launch DeskClock，同一时候都打印出来ApplicationContext的名字

Android源代码之DeskClockProxy/Delegate Application 框架应用

2.使用Proxy/Delegate框架之后使用Proxy/Delegate框架,须要又一次构建出来一个新的ProxyApplication,用来做代理Application,原先的MyApplication的作用为DelegateApplication 所以Manifest的配置须要更改,app的主入口更改为MyProxyApplication,把DelegateApplication的信息以meta-data子元素的形式存储(当然也能够用其它的方式)

< application android:name=" cn.jesse.MyProxyApplication" android:label=" @string/app_label" android:icon=" @mipmap/ic_launcher_alarmclock" android:requiredForAllUsers=" true" android:supportsRtl=" true" > < meta-data android:name=" DELEGATE_APPLICATION_CLASS_NAME" android:value=https://www.songbingjia.com/android/" cn.jesse.MyApplication" > < /meta-data> < /application>

定义一个抽象类,提供一个用于替换当前ProxyApplication 的ClassLoader成父类的ClassLoader的抽象方法(或者一些其它的个性化定制)

* Created by jesse on 15-7-17. */ public abstract class ProxyApplication extends Application{ protected abstract void initProxyApplication(); }

当我们要替换当前ProxyApplication的ClassLoader为父类的ClassLoader,所以这个替换的动作要足够得早(要保证在app Context最早被构建的入口处替换ClassLoader),要不然就会出现替换不干净的情况,就会有程序中大部分使用的DelegateApplication的ClassLoader,而一小部分是使用的ProxyApplication的ClassLoader,这样可能会出现一些意想不到的bug. 通常来说在Application的OnCreate中来做替换就足够了,可是当app有注冊ContentProvider的时候ContentProvider：OnCreate的调用是在Application:OnCreate之前的,所以我们必须保证替换ClassLoader的动作要在ContentProvider之前. 通过查看源代码能够看到Application是继承自ContextWrapper,而在ContextWrapper中系统在构建完毕完好的Context之后第一次回调是通过attachBaseContext方法,既然这样就通过在ProxyApplication中复写该方法来获取刚出炉热喷喷的Context来转换ClassLoader.

/** * Set the base context for this ContextWrapper.All calls will then be * delegated to the base context.Throws * IllegalStateException if a base context has already been set. * * @param base The new base context for this wrapper. */ protected void attachBaseContext(Context base) { if (mBase != null) { throw new IllegalStateException(" Base context already set" ); } mBase = base; }

转换ClassLoader的入口也确定之后就能够自己定义一个MyProxyApplication,继承自ProxyApplication而且复写attachBaseContext方法,print相关信息

/** * Created by jesse on 15-7-17. */ public class MyProxyApplication extends ProxyApplication { private final String TAG = MyProxyApplication.class.getSimpleName(); private Context mContext; @Override protected void attachBaseContext(Context base) { super.attachBaseContext(base); Log.i(TAG + " , attachBaseContext" ); mContext = base; this.initProxyApplication(); }@Override public void onCreate() { super.onCreate(); Log.i(TAG + " , onCreate" + this.getApplicationContext().getClass().getSimpleName()); BootLoader.boot(mContext); }@Override protected void initProxyApplication() { Log.i(TAG + " , initProxyApplication" ); BootLoader.resetClassLoader(mContext); } }

Log执行的顺序,先进入attachBaseContext-> initProxyApplication-> onCreate-> DeskClock:onCreate (这里DeskClock的onCreate获取到的ApplicationContext的名字是(MyProxyApplication)

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入口的顺序没问题了之后,就能够在initProxyApplication方法中替换当前的ClassLoader到父类的ClassLoader,而且在MyProxyApplication的onCreate中将应用层全部的Application的引用全部从ProxyApplication替换成MyApplication(当前在DeskClock程序中没有替换ClassLoader的需求,仅仅须要替换全部的Application的引用就能达到代理的效果,所以在initProxyApplication方法处就写了一个空方法带过). 先从AndroidManifest配置文件里的metadata拿到DelegateApplication的属性

String className = CLASS_NAME; ApplicationInfo appInfo = getPackageManager().getApplicationInfo(super.getPackageName(), PackageManager.GET_META_DATA); Bundle bundle = appInfo.metaData; if (bundle != null & & bundle.containsKey(KEY)) { className = bundle.getString(KEY); if (className.startsWith(" ." )) className = super.getPackageName() + className; }

依据className反射得到MyApplication,创建MyApplication实例而且取得MyProxyApplication的实例

Class delegateClass = Class.forName(className, true, getClassLoader()); Application delegate = (Application) delegateClass.newInstance(); Application proxyApplication = (Application)getApplicationContext();

使用反射更换MyProxyApplication context成员中的mOuterContext属性

Class contextImplClass = Class.forName(" android.app.ContextImpl" ); Field mOuterContext = contextImplClass.getDeclaredField(" mOuterContext" ); mOuterContext.setAccessible(true); mOuterContext.set(mContext, delegate);

获取MyProxyApplication Context的PackageInfo对象,替换掉当中的mApplication属性

Field mPackageInfoField = contextImplClass.getDeclaredField(" mPackageInfo" ); mPackageInfoField.setAccessible(true); Object mPackageInfo = mPackageInfoField.get(mContext); Class loadedApkClass = Class.forName(" android.app.LoadedApk" ); Field mApplication = loadedApkClass.getDeclaredField(" mApplication" ); mApplication.setAccessible(true); mApplication.set(mPackageInfo, delegate);

再依据之前反射得到的packageInfo对象获取到mActivityThread属性,替换掉当中的mInitialApplication属性

Class activityThreadClass = Class.forName(" android.app.ActivityThread" ); Field mAcitivityThreadField = loadedApkClass.getDeclaredField(" mActivityThread" ); mAcitivityThreadField.setAccessible(true); Object mActivityThread = mAcitivityThreadField.get(mPackageInfo); Field mInitialApplicationField = activityThreadClass.getDeclaredField(" mInitialApplication" ); mInitialApplicationField.setAccessible(true); mInitialApplicationField.set(mActivityThread, delegate);

拿着之前的mActivityThread对象获取到mAllApplications属性,注意该属性是一个list。这里就移除MyProxyApplication加入DelegateApplication,至此应用层MyProxyApplication的Context的引用所有都替换成了MyApplication的引用.

Field mAllApplicationsField = activityThreadClass.getDeclaredField(" mAllApplications" ); mAllApplicationsField.setAccessible(true); ArrayList< Application> al = (ArrayList< Application> )mAllApplicationsField.get(mActivityThread); al.add(delegate); al.remove(proxyApplication);

给MyApplication通过反射和attach内部方法设置baseContext,并调用MyApplication的onCreate方法完毕DelegateApplication的初始化.

Method attach = Application.class.getDeclaredMethod(" attach" , Context.class); attach.setAccessible(true); attach.invoke(delegate, mContext); delegate.onCreate();

完毕这些步骤之后再又一次执行查看Log,观察DeskClock处获取的ApplicationContext的名字已经变成MyApplication.

可是这样还没有全然结束,还记得开头说的ContentProvider吗?他的构造是在Application的onCreate之前的,那么ContentProvider部分有没有须要替换的Context引用呢？从framework/base/core/java/android/app下能够找到ActivityThread.java从当中装载ContentProvider的部分能够看到,假设当前Context的包名和ProviderInfo的包名一样的话,ContentProvider就会引用当前的MyProxyApplication的Context.因为当前的MyProxyApplication仅仅是做代理启动用的,所以在MyProxyApplication处复写getPackageName而且返回空就能够避免ContentProvider复用当前Context了.

private IActivityManager.ContentProviderHolder installProvider(Context context, IActivityManager.ContentProviderHolder holder, ProviderInfo info, boolean noisy, boolean noReleaseNeeded, boolean stable) { ContentProvider localProvider = null; IContentProvider provider; if (holder == null || holder.provider == null) { if (DEBUG_PROVIDER || noisy) { Slog.d(TAG, " Loading provider " + info.authority + " : " + info.name); } Context c = null; ApplicationInfo ai = info.applicationInfo; if (context.getPackageName().equals(ai.packageName)) { c = context; } else if (mInitialApplication != null & & mInitialApplication.getPackageName().equals(ai.packageName)) { c = mInitialApplication; } else { try { c = context.createPackageContext(ai.packageName, Context.CONTEXT_INCLUDE_CODE); } catch (PackageManager.NameNotFoundException e) { // Ignore } }

三.总结这篇仅仅是先简单的走了下Proxy/Delegate框架的流程,这个框架事实上是有非常多使用场景的,比如多dex动态载入,插件化,线上程序热修复bug等能够灵活使用出非常多有趣的技术,有时间的话还会再发一篇以Proxy/Delegate实现的线上程序热修复bug的博客.
【Android源代码之DeskClockProxy/Delegate Application 框架应用】转载请注明出处:http://blog.csdn.net/l2show/article/details/46914881