第二种实现android应用Theme的方式是通过apk来实现的。下面是一个demo。
1.首先必须新建一个apk，类似的插件，然后在该apk的AndroidManifest.xml文件的application加上一个meta-data。这个是下一步查找是否是自己的插件的apk做一个标记。
<meta-data android:name="skin_demo2_plugin" android:value="com.example.skindemo2.icon"/>2.在该apk添加一些图片，也可以用其他（包括style等）这里主要是为了演示。在该apk的MainActivity定义一个方法。这里主要为了方便主apk快速调用这个方法。
static int allDrawableId[] = {R.drawable.img_apparel_accessories,R.drawable.img_computers_software ,R.drawable.img_electro,R.drawable.img_electronics,R.drawable.img_entertaiment ,R.drawable.img_food_beverage,R.drawable.img_kids_baby,R.drawable.img_sport,R.drawable.img_toys_games}; public int getDrawableIdForOtherApp(int position){ if(position < allDrawableId.length){ return allDrawableId[position]; } return 0; }3.在主apk中通过读取所有安装的应用，通过分析applicationInfo的meta-data，然后判断是否是自己的插件apk。
然后通过context.createPackageContext(packageName,int flag)得到相应插件的context。然后通过类加载器得到MainActivity的class类，然后通过反射得到方法返回的值。然后就可以得到drawable对象。
package com.example.skindemo2;import java.lang.reflect.Method;import java.util.ArrayList;import java.util.List;import android.os.AsyncTask;import android.os.Bundle;import android.app.Activity;import android.content.Context;import android.content.pm.ApplicationInfo;import android.content.pm.PackageInfo;import android.content.pm.PackageManager;import android.content.pm.PackageManager.NameNotFoundException;import android.graphics.drawable.Drawable;import android.view.View;import android.widget.Button;import android.widget.ImageView;public class MainActivity extends Activity { private Button mSwtichImgBgBtn; private ImageView mShowImg; private Context context; private ArrayList<String> mPluginPackageNameList = new ArrayList<String>(); private int position = 0; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); context = this; mSwtichImgBgBtn = (Button) this.findViewById(R.id.swtichImgBgBtn); mSwtichImgBgBtn.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { swtichImgUsePlugin(); } }); mShowImg = (ImageView) this.findViewById(R.id.myShowImg); new AsyncTask<Void, Void, Void>() { @Override protected Void doInBackground(Void... params) { findPluginPackageName(); return null; } @Override protected void onPostExecute(Void result) { swtichImgUsePlugin(); super.onPostExecute(result); } }.execute(); } private void findPluginPackageName() { PackageManager pm = context.getPackageManager(); List<PackageInfo> list = pm.getInstalledPackages(0);//得到所有安装的apk的PackageInfo String meta = null; ApplicationInfo aInfo = null; for (PackageInfo pi : list) { String pkgName = pi.packageName; try { aInfo = pm.getApplicationInfo(pkgName, PackageManager.GET_META_DATA); } catch (NameNotFoundException e) { e.printStackTrace(); } if (aInfo == null || aInfo.metaData == null) continue; meta = aInfo.metaData.getString("skin_demo2_plugin"); if (meta == null || "".equals(meta)) continue; if ("com.example.skindemo2.icon".equals(meta)) { //通过meta的值判断是否是自己的插件apk mPluginPackageNameList.add(aInfo.packageName); } } } //必须在主线程中操作 private void swtichImgUsePlugin() { //我这里为了方便直接就取了第一个插件apk数据，实际中是通过用户选择的apk来切换 if (mPluginPackageNameList.size() != 0) { try { //通过createPackageContext方法得到插件apk的context Context otherplusContext = context.createPackageContext( mPluginPackageNameList.get(0), Context.CONTEXT_INCLUDE_CODE | Context.CONTEXT_IGNORE_SECURITY); //通过得到插件apk的context类加载器，然后得到MainActvity的类对象 Class<?> mainClass = otherplusContext .getClassLoader() .loadClass(mPluginPackageNameList.get(0) + ".MainActivity"); //通过反射得到相应位置的drawable Method m = mainClass.getMethod("getDrawableIdForOtherApp", int.class); int imgBgId = (Integer) m.invoke(mainClass.newInstance(), position); //为了可以循环切换img if(imgBgId == 0){ position = 0; }else{ position += 1; } //得到drawable对象 Drawable drawable = otherplusContext.getResources() .getDrawable(imgBgId); mShowImg.setImageDrawable(drawable); } catch (Exception e) { e.printStackTrace(); } } }}