第五步、爆出所有代码（为了详细点）
package com.chenyu.dexclassloaderapk; import java.io.File; import java.lang.reflect.Field; import java.lang.reflect.Method; import java.util.HashMap; import java.util.Map; import android.content.Context; import android.content.pm.ApplicationInfo; import android.content.pm.PackageInfo; import android.content.pm.PackageManager; import android.content.res.AssetManager; import android.content.res.Resources; import android.graphics.drawable.Drawable; import android.os.Bundle; import android.os.Environment; import android.support.v7.app.ActionBarActivity; import android.util.Log; import android.view.View; import android.view.View.OnClickListener; import android.widget.ImageView; import android.widget.RelativeLayout; import android.widget.TextView; import com.example.dexclassloaderapk.R; import dalvik.system.DexClassLoader; public class MainActivity extends ActionBarActivity { public static final String TAG = "DexClassLoaderApk"; public static final String PKG_NAME = "pkgName"; public static final String APK_PATH = "testClassLoader.apk"; public static final String ADDSSETPATH = "addAssetPath"; public static final String DEX = "dex"; //这个IMAGE_ID是只我放入手机里面APK 在代码里面这个图片的ID,这里我们拿到之后，然后去替换北京图片 public static final String IMAGE_ID = "about_log"; public static final String DRAWABLE = ".R$drawable"; public TextView mTextView; //背景的布局 public RelativeLayout mLayout; public Map<String, String> apkInfo; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); final String apkPath = Environment.getExternalStorageDirectory().toString() + File.separator + APK_PATH; mTextView = (TextView)findViewById(R.id.text); mLayout = (RelativeLayout)findViewById(R.id.re_Layout); mTextView.setOnClickListener(new OnClickListener(){ @Override public void onClick(View v) { //一定要记得加上android.permission.READ_EXTERNAL_STORAGE权限，不然死活都拿不到数据 //我就换了一个这个错误，如果发现代码没问题，网上找也没问题，这个时候应该思考是不是没有加权限 apkInfo = getUninstallApkInfo(MainActivity.this, apkPath); String packageName = apkInfo.get(PKG_NAME); if (null != packageName) { try { dynamicLoadApk(apkPath, packageName); } catch (Exception e) { e.printStackTrace(); Log.i(TAG, "change image fail"); } } else { Log.i(TAG, "package is null"); } } }); } /** * 获取未安装apk的信息 * @param context * @param apkPath apk文件的path * @return */ private Map<String,String> getUninstallApkInfo(Context context, String apkPath) { Map hashMap = new HashMap<String,String>(); PackageManager pm = context.getPackageManager(); PackageInfo pkgInfo = pm.getPackageArchiveInfo(apkPath, PackageManager.GET_ACTIVITIES); if (null != pkgInfo) { ApplicationInfo appInfo = pkgInfo.applicationInfo; String pkgName = appInfo.packageName;//包名 hashMap.put(PKG_NAME, pkgName); } else { Log.d(TAG, "program don't get apk package information"); } return hashMap; } /** * @param apkPath * @return 得到对应插件的Resource对象 */ private Resources getPluginResources(String apkPath) { try { AssetManager assetManager = AssetManager.class.newInstance(); //反射调用方法addAssetPath(String path) Method addAssetPath = assetManager.getClass().getMethod(ADDSSETPATH, String.class); //将未安装的Apk文件的添加进AssetManager中,第二个参数是apk的路径 addAssetPath.invoke(assetManager, apkPath); Resources superRes = this.getResources(); Resources mResources = new Resources(assetManager, superRes.getDisplayMetrics(), superRes.getConfiguration()); return mResources; } catch (Exception e) { e.printStackTrace(); } return null; } /** * 加载apk获得内部资源,并且替换背景 * @param apkDir apk目录 * @param apkName apk名字,带.apk * @throws Exception */ private void dynamicLoadApk(String apkPath, String apkPackageName) throws Exception { //在应用安装目录下创建一个名为app_dex文件夹目录,如果已经存在则不创建,这个目录主要是最优化目录，用于缓存dex文件 File optimizedDirectoryFile = getDir(DEX, Context.MODE_PRIVATE); //打印路径 理论上是/data/data/package/app_dex Log.v(TAG, optimizedDirectoryFile.getPath().toString()); //构建DexClassLoader DexClassLoader dexClassLoader = new DexClassLoader(apkPath, optimizedDirectoryFile.getPath(), null, ClassLoader.getSystemClassLoader()); //通过使用apk自己的类加载器，反射出R类中相应的内部类进而获取我们需要的资源id Class<?> clazz = dexClassLoader.loadClass(apkPackageName + DRAWABLE); //得到名为about_log的这张图片字段,这个图片是为安装apk里面的图片 Field field = clazz.getDeclaredField(IMAGE_ID); //得到图片id int resId = field.getInt(R.id.class); //得到插件apk中的Resource Resources mResources = getPluginResources(apkPath); if (mResources != null) { //通过插件apk中的Resource得到resId对应的资源 Drawable btnDrawable = mResources.getDrawable(resId); mLayout.setBackgroundDrawable(btnDrawable); } else { Log.d(TAG, "mResources is null"); } } } dynamicLoadApk(apkPath, packageName); } catch (Exception e) { e.printStackTrace(); Log.i(TAG, "change image fail"); } } else { Log.i(TAG, "package is null"); } } }); } /** * 获取未安装apk的信息 * @param context * @param apkPath apk文件的path * @return */ private Map<String,String> getUninstallApkInfo(Context context, String apkPath) { Map hashMap = new HashMap<String,String>(); PackageManager pm = context.getPackageManager(); PackageInfo pkgInfo = pm.getPackageArchiveInfo(apkPath, PackageManager.GET_ACTIVITIES); if (null != pkgInfo) { ApplicationInfo appInfo = pkgInfo.applicationInfo; String pkgName = appInfo.packageName;//包名 hashMap.put(PKG_NAME, pkgName); } else { Log.d(TAG, "program don't get apk package information"); } return hashMap; } /** * @param apkPath * @return 得到对应插件的Resource对象 */ private Resources getPluginResources(String apkPath) { try { AssetManager assetManager = AssetManager.class.newInstance(); //反射调用方法addAssetPath(String path) Method addAssetPath = assetManager.getClass().getMethod(ADDSSETPATH, String.class); //将未安装的Apk文件的添加进AssetManager中,第二个参数是apk的路径 addAssetPath.invoke(assetManager, apkPath); Resources superRes = this.getResources(); Resources mResources = new Resources(assetManager, superRes.getDisplayMetrics(), superRes.getConfiguration()); return mResources; } catch (Exception e) { e.printStackTrace(); } return null; } /** * 加载apk获得内部资源,并且替换背景 * @param apkDir apk目录 * @param apkName apk名字,带.apk * @throws Exception */ private void dynamicLoadApk(String apkPath, String apkPackageName) throws Exception { //在应用安装目录下创建一个名为app_dex文件夹目录,如果已经存在则不创建,这个目录主要是最优化目录，用于缓存dex文件 File optimizedDirectoryFile = getDir(DEX, Context.MODE_PRIVATE); //打印路径 理论上是/data/data/package/app_dex Log.v(TAG, optimizedDirectoryFile.getPath().toString()); //构建DexClassLoader DexClassLoader dexClassLoader = new DexClassLoader(apkPath, optimizedDirectoryFile.getPath(), null, ClassLoader.getSystemClassLoader()); //通过使用apk自己的类加载器，反射出R类中相应的内部类进而获取我们需要的资源id Class<?> clazz = dexClassLoader.loadClass(apkPackageName + DRAWABLE); //得到名为about_log的这张图片字段,这个图片是为安装apk里面的图片 Field field = clazz.getDeclaredField(IMAGE_ID); //得到图片id int resId = field.getInt(R.id.class); //得到插件apk中的Resource Resources mResources = getPluginResources(apkPath); if (mResources != null) { //通过插件apk中的Resource得到resId对应的资源 Drawable btnDrawable = mResources.getDrawable(resId); mLayout.setBackgroundDrawable(btnDrawable); } else { Log.d(TAG, "mResources is null"); } } }
dynamicLoadApk(apkPath, packageName);
} catch (Exception e) {
e.printStackTrace();
Log.i(TAG, "change image fail");
}
} else {
Log.i(TAG, "package is null");
}
}
});
}
/**
* 获取未安装apk的信息
* @param context
* @param apkPath apk文件的path
* @return
*/
private Map<String,String> getUninstallApkInfo(Context context, String apkPath) {
Map hashMap = new HashMap<String,String>();
PackageManager pm = context.getPackageManager();
PackageInfo pkgInfo = pm.getPackageArchiveInfo(apkPath, PackageManager.GET_ACTIVITIES);
if (null != pkgInfo) {
ApplicationInfo appInfo = pkgInfo.applicationInfo;
String pkgName = appInfo.packageName;//包名
hashMap.put(PKG_NAME, pkgName);
} else {
Log.d(TAG, "program don't get apk package information");
}
return hashMap;
}
/**
* @param apkPath
* @return 得到对应插件的Resource对象
*/
private Resources getPluginResources(String apkPath) {
try {
AssetManager assetManager = AssetManager.class.newInstance();
//反射调用方法addAssetPath(String path)
Method addAssetPath = assetManager.getClass().getMethod(ADDSSETPATH, String.class);
//将未安装的Apk文件的添加进AssetManager中,第二个参数是apk的路径
addAssetPath.invoke(assetManager, apkPath);
Resources superRes = this.getResources();
Resources mResources = new Resources(assetManager, superRes.getDisplayMetrics(), superRes.getConfiguration());
return mResources;
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
/**
* 加载apk获得内部资源,并且替换背景
* @param apkDir apk目录
* @param apkName apk名字,带.apk
* @throws Exception
*/
private void dynamicLoadApk(String apkPath, String apkPackageName) throws Exception {
//在应用安装目录下创建一个名为app_dex文件夹目录,如果已经存在则不创建,这个目录主要是最优化目录，用于缓存dex文件
File optimizedDirectoryFile = getDir(DEX, Context.MODE_PRIVATE);
//打印路径 理论上是/data/data/package/app_dex
Log.v(TAG, optimizedDirectoryFile.getPath().toString());
//构建DexClassLoader
DexClassLoader dexClassLoader = new DexClassLoader(apkPath, optimizedDirectoryFile.getPath(), null, ClassLoader.getSystemClassLoader());
//通过使用apk自己的类加载器，反射出R类中相应的内部类进而获取我们需要的资源id
Class<?> clazz = dexClassLoader.loadClass(apkPackageName + DRAWABLE);
//得到名为about_log的这张图片字段,这个图片是为安装apk里面的图片
Field field = clazz.getDeclaredField(IMAGE_ID);
//得到图片id
int resId = field.getInt(R.id.class);
//得到插件apk中的Resource
Resources mResources = getPluginResources(apkPath);
if (mResources != null) {
//通过插件apk中的Resource得到resId对应的资源
Drawable btnDrawable = mResources.getDrawable(resId);
点击TextView内容“换皮肤”来触发的，当初背景是设置的一个机器人。
第六步：运行项目爆结果照片
点击换皮护之前背景图片如下
ok,说明获取到了这种图片资源，换皮肤成功，这里只是代表换皮肤意思，效果比较丑，不要喷哈。
第七步、总结
这样做资源和宿主分离了，减轻了apk负担，同时也有解耦和作用，我们手机一些浏览器换模式（日和夜）、QQ换皮肤、表情包、线上下载线下维护、是项目更加灵活，可扩展性更好，同时也复习了DexClassLoader和反射相关知识。
