Android资源动态加载思路

   <p>在很多Android应用上，都有资源动态加载的功能，比如更换主题皮肤，替换聊天界面背景图片等。</p>    <p><img src="https://simg.open-open.com/show/b3b01b2772870e2eab6ac7d6adf2eb59.jpg"></p>    <p style="text-align:center">微信更换聊天窗口背景</p>    <p>以微信为例，当用户选择模板时，会先从网络上下载相应的图片资源，然后再替换为聊天界面的背景图片。我们知道，应用中的资源文件，包括图片，xml文件等，都是在编译的时候打包好的，那怎样才能动态加载资源呢？</p>    <p>其实有一个比较简单的思路，将需要替换的资源文件打包在一个apk文件中，动态下发到本地，然后通过重新构造Resources对象访问apk中的资源，进行本地的动态替换。主要有以下几个步骤：</p>    <h2><strong>一、指定资源文件加载路径</strong></h2>    <p>Android应用中的资源是通过AssetManager来管理的，其中addAssetPath方法可以指定资源加载路径。</p>    <pre>  <code class="language-java">/**     * Add an additional set of assets to the asset manager. This can be     * either a directory or ZIP file.  Not for use by applications.  Returns     * the cookie of the added asset, or 0 on failure.     * {@hide}     */   public final int addAssetPath(String path) {           synchronized (this) {                   int res = addAssetPathNative(path);                      makeStringBlocks(mStringBlocks);                   return res;           }   }</code></pre>    <p>很显然这是个隐藏的API，所以需要通过反射来调用。</p>    <pre>  <code class="language-java">private AssetManager createAssetManager(String skinFilePath) {        try {                  AssetManager assetManager = AssetManager.class.newInstance();                  Method addAssetPath = assetManager.getClass().getMethod("addAssetPath", String.class);                  addAssetPath.invoke(assetManager, skinFilePath);                  return assetManager;          } catch (Exception e) {                 e.printStackTrace();                 return null;          }  }</code></pre>    <h2><strong>二、构造Resources对象</strong></h2>    <pre>  <code class="language-java">private Resources createResources(Context context, AssetManager assetManager) {          Resources superRes = context.getResources();          Resources resources = new Resources(assetManager, superRes.getDisplayMetrics(), superRes.getConfiguration());            return resources;  }</code></pre>    <p>有了Resource对象，就可以访问指定路径的资源文件，进行动态替换，示例如下：</p>    <pre>  <code class="language-java">public class SkinManager {      private Resources mResources;      /**       * 获取APK资源       * @param context 上下文       * @param apkPath APK路径       */      public void loadSkinRes(Context context, String skinFilePath) {          if (TextUtils.isEmpty(skinFilePath)) {              return ;          }          try {              AssetManager assetManager = createAssetManager(skinFilePath);              mResources = createResources(context, assetManager);          } catch (Exception e) {              e.printStackTrace();          }      }        private AssetManager createAssetManager(String skinFilePath) {          try {              AssetManager assetManager = AssetManager.class.newInstance();              Method addAssetPath = assetManager.getClass().getMethod("addAssetPath", String.class);              addAssetPath.invoke(assetManager, skinFilePath);              return assetManager;          } catch (Exception e) {              e.printStackTrace();              return null;          }      }        private Resources createResources(Context context, AssetManager assetManager) {          Resources superRes = context.getResources();          Resources resources = new Resources(assetManager, superRes.getDisplayMetrics(), superRes.getConfiguration());          return resources;      }        public Resources getSkinResource() {          return mResources;      }  }</code></pre>    <p>在进入Activity的时候进行检查，如果有资源apk文件，则通过新的Resources对象进行资源获取。</p>    <pre>  <code class="language-java">public class MainActivity extends Activity {        private Context mContext;      private ImageView mBgView;      private SkinManager mSkinManager;        @Override      protected void onCreate(Bundle savedInstanceState) {          super.onCreate(savedInstanceState);          setContentView(R.layout.activity_main);          mBgView = (ImageView) findViewById(R.id.bg);          mContext = this;          mSkinManager = new SkinManager();          checkNewSkin();      }        private void checkNewSkin() {          String skinDir = "/mnt/sdcard/skin";          File file = new File(skinDir);          File[] skinFile = file.listFiles();          if (skinFile == null || skinFile.length == 0) {              return ;          }          mSkinManager.loadSkinRes(mContext, skinFile[0].getAbsolutePath());          if (mSkinManager.getSkinResource() != null) {              mBgView.setBackgroundDrawable(mSkinManager.getSkinResource().getDrawable(R.mipmap.skin));          }     }  }</code></pre>    <p>这里是非常简单的处理，将编译好的资源apk文件push到本地sd卡直接加载，正常情况下应该是从网络下载，根据不同的模板名称进行资源的动态替换。</p>    <p> </p>    <p>来自：http://www.jianshu.com/p/e6125ddfaea7</p>    <p> </p>