Android LayoutInflater inflate方法效率

很多Android开发可能知道, LayoutInflater.inflate()方法是个耗时操作, 应尽量避免调用.

我也曾经非常担心在Adapter和ViewGroup动态循环添加View时耗时太多, 但是感觉Android应该会有个布局xml的解析缓存, 今天看了下Android的源码, 果然如此. 在第一次调用inflate相应布局xml时会比较耗时, 之后就会很快!

下面贴上核心源码:

1. 在LayoutInflater中:    public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot) {        final Resources res = getContext().getResources();        if (DEBUG) {            Log.d(TAG, "INFLATING from resource: \"" + res.getResourceName(resource) + "\" ("                    + Integer.toHexString(resource) + ")");        }        // 获取布局xml的parser        final XmlResourceParser parser = res.getLayout(resource);        try {            return inflate(parser, root, attachToRoot);        } finally {            parser.close();        }    }

2. 在Resources中:    @NonNull    XmlResourceParser loadXmlResourceParser(@AnyRes int id, @NonNull String type)            throws NotFoundException {        final TypedValue value = obtainTempTypedValue();        try {

3. 在ResourcesImpl中, 首先读取缓存, 如果缓存中不存在, 再去实际读取文件, 解析加载    @NonNull    XmlResourceParser loadXmlResourceParser(@NonNull String file, @AnyRes int id, int assetCookie,            @NonNull String type)            throws NotFoundException {        if (id != 0) {            try {                synchronized (mCachedXmlBlocks) {                    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)) {                            // 已经由缓存, 返回缓存                            return cachedXmlBlocks[i].newParser();                        }                    }                    // 没缓存, 解析加载                    // 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();                    }                }            } 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));    }

final ResourcesImpl impl = mResourcesImpl; impl.getValue(id, value, true); if (value.type == TypedValue.TYPE_STRING) { // 用ResourcesImpl 实际获取布局xml的Parser 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 { releaseTempTypedValue(value); } }

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