1). 换肤思路

在源应用APP中，下载皮肤包，使得对应的文件资源得以应用。使用DexClassLoader加载资源包，使用反射来获取资源ID.

2). 创建SkinChange工程

图1.png

app是应用Module，spinone和spintwo是皮肤插件工程

3). app Module

• BaseActivity

/*** Activity基类* Created by mazaiting on 2018/6/27.*/public abstract class BaseActivity extends AppCompatActivity {/**资源管理器*/protected AssetManager mAssetManager;/**资源*/protected Resources mResources;/**主题*/protected Theme mTheme;/*** 加载资源* @param dexPath dex路径*/protected void loadResources(String dexPath) {try {AssetManager assetManager = AssetManager.class.newInstance();Method addAssetPath = assetManager.getClass().getMethod("addAssetPath",String.class);addAssetPath.invoke(assetManager, dexPath);mAssetManager = assetManager;} catch (Exception e) {e.printStackTrace();}Resources superRes = super.getResources();superRes.getDisplayMetrics();superRes.getConfiguration();mResources = new Resources(mAssetManager, superRes.getDisplayMetrics(), superRes.getConfiguration());mTheme = mResources.newTheme();mTheme.setTo(super.getTheme());}@Overridepublic AssetManager getAssets() {return mAssetManager == null ? super.getAssets() : mAssetManager;}@Overridepublic Resources getResources() {return mResources == null ? super.getResources() : mResources;}@Overridepublic Theme getTheme() {return mTheme == null ? super.getTheme() : mTheme;}
}

• MainActivity

public class MainActivity extends BaseActivity {private static final String TAG = "MainActivity";private TextView mTextView;private ImageView mImageView;private ClassLoader mClassLoader;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);mTextView = findViewById(R.id.tv_show);mImageView = findViewById(R.id.iv_show);}/*** 切换主题1*/public void changeThemeOne(View view) {// 获取缓存路径String fileDir = getCacheDir().getAbsolutePath();// 获取文件路径String filePath = fileDir + File.separator + "spinone-release.apk";mClassLoader = new DexClassLoader(filePath, fileDir, null, getClassLoader());loadResources(filePath);setContentOne();}/*** 切换主题2*/public void changeThemeTwo(View view) {// 获取缓存路径String fileDir = getCacheDir().getAbsolutePath();// 获取文件路径String filePath = fileDir + File.separator + "spintwo-release.apk";mClassLoader = new DexClassLoader(filePath, fileDir, null, getClassLoader());loadResources(filePath);setContent();}/*** 设置主题内容*/private void setContent() {try {Class clazz = mClassLoader.loadClass("com.mazaiting.UiUtil");// 设置TextView内容Method method = clazz.getMethod("getTextString", Context.class);String string = (String) method.invoke(null, this);mTextView.setText(string);// 设置ImageView背景method = clazz.getMethod("getImageDrawable",Context.class);Drawable drawable = (Drawable) method.invoke(null,this);mImageView.setBackground(drawable);} catch (Exception e) {e.printStackTrace();}}/*** 设置主题1*/private void setContentOne() {int stringId = getTextStringId();int drawableId = getImgDrawableId();Log.d(TAG, "stringId: " + stringId + ",  drawableId: " + drawableId);}/*** 获取图片ID* @return*/private int getImgDrawableId() {try {// "com.mazaiting.spinone.R$color" -- spinone module 下的R.color.imgClass clazz = mClassLoader.loadClass("com.mazaiting.spinone.R$color");Field field = clazz.getField("img");int resId = (int) field.get(null);return resId;} catch (Exception e) {e.printStackTrace();}return 0;}/*** 获取字符串ID* @return*/private int getTextStringId() {try {// "com.mazaiting.spinone.R$string" -- spinone module下的R.string.textClass clazz = mClassLoader.loadClass("com.mazaiting.spinone.R$string");Field field = clazz.getField("text");int resId = (int) field.get(null);return resId;} catch (Exception e) {e.printStackTrace();}return 0;}
}

• activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayoutxmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"tools:context="com.mazaiting.skinchange.MainActivity"><LinearLayoutandroid:layout_width="match_parent"android:layout_height="wrap_content"><Buttonandroid:onClick="changeThemeOne"android:text="主题1"android:layout_width="wrap_content"android:layout_height="wrap_content"/><Buttonandroid:onClick="changeThemeTwo"android:text="主题2"android:layout_width="wrap_content"android:layout_height="wrap_content"/></LinearLayout><LinearLayoutandroid:paddingTop="50dp"android:layout_width="match_parent"android:layout_height="wrap_content"android:orientation="vertical"><TextViewandroid:id="@+id/tv_show"android:text="@string/text"android:layout_width="match_parent"android:layout_height="wrap_content"/><ImageViewandroid:id="@+id/iv_show"android:background="@color/img"android:layout_width="200dp"android:layout_height="200dp"/></LinearLayout></android.support.constraint.ConstraintLayout>

• 资源文件

  

  图2.png

4). 插件Module

spinone和spintwo中同样使用一个类，包的全路径名与MainActivity中setContent方法中的Class clazz = mClassLoader.loadClass("com.mazaiting.UiUtil");中com.mazaiting.UiUtil相同。并在插件Module中使用相同的资源文件名进行替换。

package com.mazaiting;
/*** Created by mazaiting on 2018/6/27.*/public class UiUtil {/*** 获取字符串*/public static String getTextString(Context ctx) {return ctx.getResources().getString(R.string.text);}/*** 获取图片*/public static Drawable getImageDrawable(Context ctx) {return ctx.getResources().getDrawable(R.color.img);}public static int getTextStringId(){return R.string.text;}public static int getImageDrawableId(){return R.color.img;}
}

5). 运行

安装app Module 至手机，spinone和spintwo Module打包为apk文件，使用命令安装至手机，此处必须将spinone-release.apk文件push到/data/data/<包名>/cache/目录下

adb push C:\Users\mazaiting\Desktop\release\s
pinone-release.apk /data/data/com.mazaiting.skinchange/cache

示例效果：

图4.gif

6). 残留的问题

• 每个插件包都包含一个UiUtil文件，造成代码冗余（主题2的加载）
• 主工程无法获取插件包的应用包名，从而实现动态加载。（主题1的加载）（能想到的解决办法：插件的文件名即包名）

代码下载