Android Resource.getLayout函数分析-（基于10.0.0）

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在分析LayoutInflater的时候有一处是需要根据资源ID生成一个XmlResourceParser对象的，这个是通过调用Resource类的getLayout函数实现的，该函数的代码如下

/frameworks/base/core/java/android/content/res/Resources.java

    public XmlResourceParser getLayout(@LayoutRes int id) throws NotFoundException {return loadXmlResourceParser(id, "layout");}

可以看出它内部是调用loadXmlResourceParser并传入“layou”来实现，看来loadXmlResourceParser函数是用来解析多种类别xml的,在Resources类中 getLayout、getAnimation、getXml都是在内部直接调用loadXmlResourceParser的，我们继续往下看

/frameworks/base/core/java/android/content/res/Resources.java

    XmlResourceParser loadXmlResourceParser(@AnyRes int id, @NonNull String type) throws NotFoundException {// 获取一个TypedValue对象，这里使用了一个单Item的对象池，减小对象的申请和释放final TypedValue value = obtainTempTypedValue();try {final ResourcesImpl impl = mResourcesImpl;// 根据资源ID获取对应的文件路径，然后把相关信息存储在value里面impl.getValue(id, value, true);if (value.type == TypedValue.TYPE_STRING) {// 根据文件路径创建XML解释器return impl.loadXmlResourceParser(value.string.toString(), id,value.assetCookie, type);}throw new NotFoundException("Resource ID #0x" + Integer.toHexString(id)+ " type #0x" + Integer.toHexString(value.type) + " is not valid");} finally {// 将TypeValue对象归还给对象池releaseTempTypedValue(value);}}

先调用ResourcesImpl类的getValue函数获取XML文件的路径

/frameworks/base/core/java/android/content/res/ResourcesImpl.java

 void getValue(@AnyRes int id, TypedValue outValue, boolean resolveRefs)throws NotFoundException {boolean found = mAssets.getResourceValue(id, 0, outValue, resolveRefs);if (found) {return;}throw new NotFoundException("Resource ID #0x" + Integer.toHexString(id));}

在getValue中实际上调用了AssetManager.getResourceValue(); AssetManager是Android中的资源管理类，下一篇文章我们分析它

在通过AssetManager获取到资源ID对应的文件路径后调用ResourcesImpl类中的loadXmlResourceParser函数来获取XMLResourceParser

/frameworks/base/core/java/android/content/res/ResourcesImpl.java

XmlResourceParser loadXmlResourceParser(@NonNull String file, @AnyRes int id, int assetCookie,@NonNull String type)throws NotFoundException {if (id != 0) {try {synchronized (mCachedXmlBlocks) {// 在缓存中找已经缓存的XmlBlock，XmlBlock是一个编译过的xml文件final int[] cachedXmlBlockCookies = mCachedXmlBlockCookies;final String[] cachedXmlBlockFiles = mCachedXmlBlockFiles;final XmlBlock[] cachedXmlBlocks = mCachedXmlBlocks;// First see if this block is in our cache.final int num = cachedXmlBlockFiles.length;for (int i = 0; i < num; i++) {if (cachedXmlBlockCookies[i] == assetCookie && cachedXmlBlockFiles[i] != null&& cachedXmlBlockFiles[i].equals(file)) {return cachedXmlBlocks[i].newParser(id);}}// 没有已缓存的XmlBlock，就新建一个，并返回// Not in the cache, create a new block and put it at// the next slot in the cache.final XmlBlock block = mAssets.openXmlBlockAsset(assetCookie, file);if (block != null) {final int pos = (mLastCachedXmlBlockIndex + 1) % num;mLastCachedXmlBlockIndex = pos;final XmlBlock oldBlock = cachedXmlBlocks[pos];if (oldBlock != null) {oldBlock.close();}cachedXmlBlockCookies[pos] = assetCookie;cachedXmlBlockFiles[pos] = file;cachedXmlBlocks[pos] = block;return block.newParser(id);}}} catch (Exception e) {final NotFoundException rnf = new NotFoundException("File " + file+ " from xml type " + type + " resource ID #0x" + Integer.toHexString(id));rnf.initCause(e);throw rnf;}}throw new NotFoundException("File " + file + " from xml type " + type + " resource ID #0x"+ Integer.toHexString(id));}

到此我们就知道XmlResourceParser是怎么来的了

 

 

 

 

 

 

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