Improve DocumentFile performance

CachedDocumentFile.java

package android.support.v4.provider;

import android.net.Uri;
import android.support.v4.provider.DocumentFile;

public class CachedDocumentFile extends DocumentFile {

	final DocumentFile mWrapped;
	final boolean mCacheChildren;
	
	Boolean mCanRead;
	Boolean mCanWrite;
	Boolean mExists;
	String mName;
	String mType;
	Boolean mIsDirectory;
	// Boolean mIsFile;
	Long mLastModified;
	Long mLength;
	DocumentFile[] mListFiles;
	
	public void invalidate() {
		mCanRead = null;
		mCanWrite = null;
		mExists = null;
		mName = null;
		mType = null;
		mIsDirectory = null;
		//mIsFile = null;
		mLastModified = null;
		mLength = null;
		mListFiles = null;
	}
	
	public CachedDocumentFile(DocumentFile wrapped) {
		this(wrapped, true);
	}
	
	public CachedDocumentFile(DocumentFile wrapped, boolean cacheChildren) {
		super(wrapped.getParentFile());
		mWrapped = wrapped;
		mCacheChildren = cacheChildren;
	}

	@Override
	public boolean canRead() {
		if(mCanRead == null) {
			mCanRead = mWrapped.canRead();
		}
		return mCanRead;
	}

	@Override
	public boolean canWrite() {
		if(mCanWrite == null) {
			mCanWrite = mWrapped.canWrite();
		}
		return mCanWrite;

	}

	@Override
	public DocumentFile createDirectory(String arg0) {
		return mWrapped.createDirectory(arg0);
	}

	@Override
	public DocumentFile createFile(String arg0, String arg1) {
		return mWrapped.createFile(arg0, arg1);
	}

	@Override
	public boolean delete() {
		if(mWrapped.delete()) {
			invalidate();
			return true;
		}
		return false;
	}

	@Override
	public boolean exists() {
		if(mExists == null) {
			mExists = mWrapped.exists();
		}
		return mExists;
	}

	@Override
	public String getName() {
		if(mName == null) {
			mName = mWrapped.getName();
		}
		return mName;
	}

	@Override
	public String getType() {
		if(mType == null) {
			mType = mWrapped.getType();
		}
		return mType;
	}

	@Override
	public Uri getUri() {
		return mWrapped.getUri();
	}

	@Override
	public boolean isDirectory() {
		if(mIsDirectory == null) {
			mIsDirectory = mWrapped.isDirectory();
		}
		return mIsDirectory;
	}

	@Override
	public boolean isFile() {
		return !isDirectory();
		/*
		if(mIsFile == null) {
			mIsFile = mWrapped.isFile();
		}
		return mIsFile;
		*/
	}

	@Override
	public long lastModified() {
		if(mLastModified == null) {
			mLastModified = mWrapped.lastModified();
		}
		return mLastModified;
	}

	@Override
	public long length() {
		if(mLength == null) {
			mLength = mWrapped.length();
		}
		return mLength;
	}

	@Override
	public DocumentFile[] listFiles() {
		if(mListFiles == null) {
			mListFiles = mWrapped.listFiles();
			if(mCacheChildren) {
				for(int i = 0 ; i < mListFiles.length ; i++) {
					mListFiles[i] = new CachedDocumentFile(mListFiles[i]);
				}
			}
		}
		return mListFiles;
	}

	@Override
	public boolean renameTo(String arg0) {
		if(mWrapped.renameTo(arg0)) {
			invalidate();
			return true;
		}
		return false;
	}

}