Does inflate cache xml layouts?

Question

When we inflate a layout does it get cached? If I recall correctly I have read that the inflate caches XML for performance. Is that correct? What exactly is being cached?

@MD: So it re-reads the XML file from the FS each time we inflate? — Jim, Jul 17 '17 at 07:24
if any caching is done, it is on system level (file system cache), not app level — pskink, Jul 17 '17 at 07:28
@MD: I am not talking about lists and the holder pattern. I thought that there was some optimization for inflate — Jim, Jul 17 '17 at 07:42
The optimization applied is some sort of compression and binarization of the xmls for faster parsing. But i don't think there is caching by default. — WindRider, Sep 18 '17 at 18:47

score 1 · Answer 1 · answered Jul 21 '20 at 09:59

From ResourcesImpl class under android.content.res, I got some clues that there is an internal caching mechanism while inflating a view from XML.In inflater.inflate() there is an XmlResourceParser object which is responsible for parsing XML. And this object is got from a method named loadXmlResourceParser in the ResourcesImpl class. The method is -

 /**
 * Loads an XML parser for the specified file.
 *
 * @param file the path for the XML file to parse
 * @param id the resource identifier for the file
 * @param assetCookie the asset cookie for the file
 * @param type the type of resource (used for logging)
 * @return a parser for the specified XML file
 * @throws NotFoundException if the file could not be loaded
 */
@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)) {
                        return cachedXmlBlocks[i].newParser();
                    }
                }

                // Not in the cache, create a new block and put it at
                // the next slot in the cache. (EVIDENCE FOR CACHING)
                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));
}

Does inflate cache xml layouts?

1 Answers1