Resources 资源加载

加载res中的资源，都是通过getResources()获取的，但是Resources是在什么时候被创建的呢，如何通过Resources获取到对应的资源的呢？

XmlResourceParser layout = getResources().getLayout(R.layout.activity_change_skin);
int color = getResources().getColor(R.color.color_e83b36);
Drawable drawable = getResources().getDrawable(R.drawable.image_liu);

ContextThemeWrapper的getResources()

@Override
public Resources getResources() {return getResourcesInternal();
}

ContextThemeWrapper的getResourcesInternal()：

1. mResources为null，根据mOverrideConfiguration来判断是从ContextImpl类中获取还是创建之后再获取；
2. mResources不为null，则直接返回；

private Resources getResourcesInternal() {if (mResources == null) {//为null，则直接从ContextImpl类中获取；if (mOverrideConfiguration == null) {mResources = super.getResources();} else {//不为null,则通过ContextImpl类的createConfigurationContext()方法创建；final Context resContext = createConfigurationContext(mOverrideConfiguration);mResources = resContext.getResources();}}return mResources;
}

跳过中间的跳转，直接定位到ContextImpl的createConfigurationContext()方法

@Override
public Context createConfigurationContext(Configuration overrideConfiguration) {//创建ContextImpl对象；ContextImpl context = new ContextImpl(this, mMainThread, mPackageInfo, mSplitName,mActivityToken, mUser, mFlags, mClassLoader);final int displayId = mDisplay != null ? mDisplay.getDisplayId() : Display.DEFAULT_DISPLAY;//通过createResources()方法创建Resources对象；并赋值给mResources；context.setResources(createResources(mActivityToken, mPackageInfo, mSplitName, displayId,overrideConfiguration, getDisplayAdjustments(displayId).getCompatibilityInfo()));return context;
}

ContextImpl的createResources()

private static Resources createResources(IBinder activityToken, LoadedApk pi, String splitName,int displayId, Configuration overrideConfig, CompatibilityInfo compatInfo) {final String[] splitResDirs;final ClassLoader classLoader;try {splitResDirs = pi.getSplitPaths(splitName);classLoader = pi.getSplitClassLoader(splitName);} catch (NameNotFoundException e) {throw new RuntimeException(e);}//调用ResourcesManager的getResources();return ResourcesManager.getInstance().getResources(activityToken,pi.getResDir(),splitResDirs,pi.getOverlayDirs(),pi.getApplicationInfo().sharedLibraryFiles,displayId,overrideConfig,compatInfo,classLoader);
}

ResourcesManager的getResources()；获取或者创建Resources对象；

public @Nullable Resources getResources(@Nullable IBinder activityToken,@Nullable String resDir,@Nullable String[] splitResDirs,@Nullable String[] overlayDirs,@Nullable String[] libDirs,int displayId,@Nullable Configuration overrideConfig,@NonNull CompatibilityInfo compatInfo,@Nullable ClassLoader classLoader) {try {Trace.traceBegin(Trace.TRACE_TAG_RESOURCES, "ResourcesManager#getResources");final ResourcesKey key = new ResourcesKey(resDir,splitResDirs,overlayDirs,libDirs,displayId,overrideConfig != null ? new Configuration(overrideConfig) : null, // CopycompatInfo);classLoader = classLoader != null ? classLoader : ClassLoader.getSystemClassLoader();return getOrCreateResources(activityToken, key, classLoader);} finally {Trace.traceEnd(Trace.TRACE_TAG_RESOURCES);}
}

getOrCreateResources()：是最终获取或则创建Resources的方法，来详细看下系统 是如何创建的；我们主要看第三种情况

1. activityToken不为空，则通过key获取ResourcesImpl对象，然后通过getOrCreateResourcesForActivityLocked()方法获取或者创建一个Resources对象；
2. activityToken为空，则通过key获取ResourcesImpl对象，然后getOrCreateResourcesLocked()获取或者创建一个Resources对象
3. 如果不存在key对应的ResourcesImpl对象，则通过createResourcesImpl()创建ResourcesImpl对象，再根据activityToken是否为null，调用对应的方法，创建Resources对象；

private @Nullable Resources getOrCreateResources(@Nullable IBinder activityToken,@NonNull ResourcesKey key, @NonNull ClassLoader classLoader) {synchronized (this) {//1:activityToken不为null;if (activityToken != null) {final ActivityResources activityResources =getOrCreateActivityResourcesStructLocked(activityToken);// Clean up any dead references so they don't pile up.ArrayUtils.unstableRemoveIf(activityResources.activityResources,sEmptyReferencePredicate);// Rebase the key's override config on top of the Activity's base override.if (key.hasOverrideConfiguration()&& !activityResources.overrideConfig.equals(Configuration.EMPTY)) {final Configuration temp = new Configuration(activityResources.overrideConfig);temp.updateFrom(key.mOverrideConfiguration);key.mOverrideConfiguration.setTo(temp);}//通过Key获取对应的ResourcesImpl对象；ResourcesImpl resourcesImpl = findResourcesImplForKeyLocked(key);if (resourcesImpl != null) {return getOrCreateResourcesForActivityLocked(activityToken, classLoader,resourcesImpl, key.mCompatInfo);}// We will create the ResourcesImpl object outside of holding this lock.} else {//2:activityToken为null;// Clean up any dead references so they don't pile up.ArrayUtils.unstableRemoveIf(mResourceReferences, sEmptyReferencePredicate);// Not tied to an Activity, find a shared Resources that has the right ResourcesImplResourcesImpl resourcesImpl = findResourcesImplForKeyLocked(key);if (resourcesImpl != null) {return getOrCreateResourcesLocked(classLoader, resourcesImpl, key.mCompatInfo);}// We will create the ResourcesImpl object outside of holding this lock.}}//3:创建一个ResourcesImpl对象；ResourcesImpl resourcesImpl = createResourcesImpl(key);if (resourcesImpl == null) {return null;}//再次通过key获取对应的ResourcesImpl对象，判断是否存在，不存在加入ArrayMap中；synchronized (this) {ResourcesImpl existingResourcesImpl = findResourcesImplForKeyLocked(key);if (existingResourcesImpl != null) {resourcesImpl.getAssets().close();resourcesImpl = existingResourcesImpl;} else {// Add this ResourcesImpl to the cache.mResourceImpls.put(key, new WeakReference<>(resourcesImpl));}//根据activityToken是否为null,判断如何创建Resources对象；final Resources resources;if (activityToken != null) {resources = getOrCreateResourcesForActivityLocked(activityToken, classLoader,resourcesImpl, key.mCompatInfo);} else {resources = getOrCreateResourcesLocked(classLoader, resourcesImpl, key.mCompatInfo);}return resources;}
}

createResourcesImpl()：系统是如何创建ResourcesImpl对象的，主要参数：AssetManager对象；

AssetManager类；通过createAssetManager()方法，创建AssetManager对象；可以通过addXXX()方法根据path加载资源；

ResourcesImpl是资源访问的实现，包含AssetManager和与之关联的所有缓存；Resources是Resources的包装类，Resources中的方法都是通过ResourcesImpl对象来实现的；

private @Nullable ResourcesImpl createResourcesImpl(@NonNull ResourcesKey key) {final DisplayAdjustments daj = new DisplayAdjustments(key.mOverrideConfiguration);daj.setCompatibilityInfo(key.mCompatInfo);//根据路径创建AssetManager对象；并且根据path获取资源；final AssetManager assets = createAssetManager(key);if (assets == null) {return null;}final DisplayMetrics dm = getDisplayMetrics(key.mDisplayId, daj);final Configuration config = generateConfig(key, dm);//创建ResourcesImpl对象；final ResourcesImpl impl = new ResourcesImpl(assets, dm, config, daj);if (DEBUG) {Slog.d(TAG, "- creating impl=" + impl + " with key: " + key);}return impl;
}

AssetManager类中主要的方法

//通过路径添加额外的资源，可以是目录或者zip；失败则返回0；
public final int addAssetPath(String path) {return  addAssetPathInternal(path, false);
}private final int addAssetPathInternal(String path, boolean appAsLib) {synchronized (this) {int res = addAssetPathNative(path, appAsLib);makeStringBlocks(mStringBlocks);return res;}
}
//native方法；
private native final int addAssetPathNative(String path, boolean appAsLib);

不管activityToken是否为null，调用getOrCreateResourcesForActivityLocked()还是getOrCreateResourcesLocked()都是类似的，都是遍历集合判断classLoader和impl是否相等，满足条件直接返回；否则创建对象

if (resources != null&& Objects.equals(resources.getClassLoader(), classLoader)&& resources.getImpl() == impl) {return resources;
}

不满足上述条件，直接创建对象；

//创建Resources对象；
Resources resources = compatInfo.needsCompatResources() ? new CompatResources(classLoader): new Resources(classLoader);
//调用setImpl()将ResourcesImpl对象传给Resources对象；
resources.setImpl(impl);
mResourceReferences.add(new WeakReference<>(resources));

系统是如何加载资源的Res资源的呢？

• 创建AssetManager对象，调用addXXXPath()方法，读取对应路径下的资源文件；并添加到ArrayMap对象mResourceImpls中；然后创建ResourcesImpl对象；
• 以ClassLoader对象作为参数创建Resources对象，并setImpl()设置ResourcesImpl对象；

上述是如何获取或者创建Resources对象；有了Resources对象之后，如何获取对应的资源呢？

Resources中的资源文件，如何生成对应的ID的？

具体详见Android应用程序资源的编译和打包过程分析

以Resources的getText()方法为例，会调用AssetManager的getResourceText()方法；

@NonNull public CharSequence getText(@StringRes int id) throws NotFoundException {CharSequence res = mResourcesImpl.getAssets().getResourceText(id);if (res != null) {return res;}throw new NotFoundException("String resource ID #0x"+ Integer.toHexString(id));
}

AssetManager的getResourceText()

@Nullable
final CharSequence getResourceText(@StringRes int resId) {synchronized (this) {final TypedValue outValue = mValue;if (getResourceValue(resId, 0, outValue, true)) {return outValue.coerceToString();}return null;}
}

getResourceValue()方法

final boolean getResourceValue(@AnyRes int resId, int densityDpi, @NonNull TypedValue outValue,boolean resolveRefs) {synchronized (this) {//native方法final int block = loadResourceValue(resId, (short) densityDpi, outValue, resolveRefs);if (block < 0) {return false;}// Convert the changing configurations flags populated by native code.outValue.changingConfigurations = ActivityInfo.activityInfoConfigNativeToJava(outValue.changingConfigurations);if (outValue.type == TypedValue.TYPE_STRING) {outValue.string = mStringBlocks[block].get(outValue.data);}return true;}
}

引入外部资源

我们平时都是使用APP内部的资源文件，除了一键换肤，插件化开发，很少有引入外部资源文件的情况；我们如何如何APP之外的资源文件呢？

通过反射的方式创建Assetmanager，ResourcesImpl，Resources对象；

public class OutResources {private String TAG = OutResources.class.getSimpleName();private Resources resources;private static OutResources outResources;private String mOutPkgName;private String mFilePath;private OutResources() {}public static OutResources getInstance() {if (outResources == null) {synchronized (OutResources.class) {if (outResources == null) {outResources = new OutResources();}}}return outResources;}/*** 创建Resources对象；* <p>* Resources对外公开的构造方法*/void initResources(String filePath) {this.mFilePath = filePath;try {if (resources == null) {//通过反射的方式获取AssetManager assetManager = createAssetManager();if (assetManager == null) {return;}Resources superRes = MyApplication.getContext().getResources();resources = new Resources(assetManager, superRes.getDisplayMetrics(), superRes.getConfiguration());}Log.e(TAG, "加载外部资源文件");} catch (Exception e) {e.printStackTrace();}}//第二种，按照系统的方式创建Resources对象void initRes(String filePath) {this.mFilePath = filePath;if (resources == null) {//创建Resources对象；resources = (Resources) RefInvoke.createObject(Resources.class);AssetManager assetManager = createAssetManager();if (assetManager == null) {return;}Resources superRes = MyApplication.getContext().getResources();DisplayMetrics displayMetrics = superRes.getDisplayMetrics();Configuration configuration = superRes.getConfiguration();//获取DisplayAdjustments的class对象和实例；Class disCls = null;try {disCls = Class.forName("android.view.DisplayAdjustments");} catch (Exception e) {e.printStackTrace();}Object dis = RefInvoke.createObject(disCls);String className = "android.content.res.ResourcesImpl";Class[] pareTyples = {AssetManager.class, DisplayMetrics.class, Configuration.class, disCls};Object[] values = {assetManager, displayMetrics, configuration, dis};//创建ResourcesImpl实例；Object resourcesImpl = RefInvoke.createObject(className, pareTyples, values);Class resourcesImplClass = null;try {resourcesImplClass = Class.forName(className);} catch (Exception e) {e.printStackTrace();}//调用Resources的setImpl()方法；RefInvoke.invokeInstanceMethod(resources, "setImpl", resourcesImplClass, resourcesImpl);}Log.e(TAG, "加载外部资源文件");}/*** 1）相同的资源名称，在不同的APK中，编译后对应的ID会不同；** @param resId* @return*/public Drawable getDrawable(Context context, int resId) {//获取图片//Application mContext = context.getApplication();if (resources == null) {return ContextCompat.getDrawable(context, resId);}//包名+资源名String resName = context.getResources().getResourceName(resId);//资源名String name = context.getResources().getResourceEntryName(resId);//包名String packageName = context.getResources().getResourcePackageName(resId);//对应资源的类型；String typeName = context.getResources().getResourceTypeName(resId);Log.e(TAG, "resName::" + resName);//需要获取的资源的包名；如果不存在对应的ID，获取不到包名；//String mOutPkgName = resources.getResourcePackageName(resId);//通过资源名称，类型获取对应的资源ID；int outResId = resources.getIdentifier(name, typeName, mOutPkgName);//outResId 没有这样的资源被发现；if (outResId == 0) {return ContextCompat.getDrawable(context, resId);}Log.e(TAG, "resId;;" + R.drawable.image_liu + ",,,outResId::" + outResId);return resources.getDrawable(outResId);}public int getColor(Context context, @ColorRes int id) {if (resources == null) {return ContextCompat.getColor(context, id);}Resources superRes = context.getResources();String packageName = superRes.getResourcePackageName(id);String name = superRes.getResourceEntryName(id);String typeName = superRes.getResourceTypeName(id);int outResId = resources.getIdentifier(name, typeName, mOutPkgName);if (outResId == 0) {return ContextCompat.getColor(context, id);}return resources.getColor(outResId);}private AssetManager createAssetManager() {try {Class<AssetManager> assetManagerClass = AssetManager.class;//AssetManager assetManager = (AssetManager) RefInvoke.createObject(clazz);//调用AssetManager的getSystem()方法；AssetManager assetManager = (AssetManager) RefInvoke.invokeStaticMethod(assetManagerClass, "getSystem");Log.e(TAG, "filePath::" + mFilePath);getPackageName(mFilePath);//调用addAssetPath()加载第三方资源；int addAssetPath = (int) RefInvoke.invokeInstanceMethod(assetManager, "addAssetPath", String.class, mFilePath);Log.e(TAG, "addAssetPath::" + addAssetPath);if (addAssetPath == 0) {Log.e(TAG, "加载资源失败");}return assetManager;} catch (Exception e) {e.printStackTrace();}return null;}private void getPackageName(String filePath) {//取得PackageManager引用PackageManager mPm = MyApplication.getContext().getPackageManager();//“检索在包归档文件中定义的应用程序包的总体信息”，说人话，外界传入了一个apk的文件路径，这个方法，//拿到这个apk的包信息,这个包信息包含什么？PackageInfo mInfo = mPm.getPackageArchiveInfo(filePath, PackageManager.GET_ACTIVITIES);//先把包名存起来mOutPkgName = mInfo.packageName;}

然后在点击事件中调用下面两个方法，即可加载app.zip的image_liu资源（app.zip中必须有和相同名称的资源，由apk包改为zip类型文件）；

//可以放在Application中或者MainActivity；
private void initRes() {String filePath = Environment.getExternalStorageDirectory() + File.separator + "a_test_change/app.zip";OutResources.getInstance().initRes(filePath);
}private void loadImage() {imageView.setImageDrawable(OutResources.getInstance().getDrawable(act, R.drawable.image_liu));
}

以上就是Recouces的主要内容了，如有问题，请多指教，谢谢！