Android LayoutInflater inflate方法效率

最新推荐文章于 2024-07-01 14:09:00 发布

David_Ding

最新推荐文章于 2024-07-01 14:09:00 发布

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分类专栏： Android 文章标签： LayoutInflater inflate Android 效率

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本文探讨了Android中LayoutInflater.inflate()方法的性能问题，并详细解释了其内部的缓存机制。首次加载布局文件时可能会稍慢，但之后的加载过程会变得非常快，这是因为系统会在内存中缓存布局文件。

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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); } }