* @return false - some files could not deleted, but continue.
	 */
	protected boolean cleanDirectory(final File targetDirectory) {
		boolean result = true;
		String[] filenames = targetDirectory.list(new FilenameFilter() {
			@Override public boolean accept(File dir, String name) {
				if (targetDirectory.equals(dir)) {
					if (!IOSImageUtil.isNullOrWhiteSpace(name)) {
						if (name.toLowerCase().trim().endsWith(".png")) {
							return true;
						}
						if (name.toLowerCase().trim().endsWith(".json")) {
							return true;
						}
					}
				}
				return false;
			}
		});
		for (String filename : filenames) {
			File f = new File(targetDirectory, filename);
			if (f.exists() && f.isFile()) {
				if (!f.delete()) {
					System.err.println("Could not delete file - " + f.getAbsolutePath());
					result = false;
				}
			}
		}
		return result;
	}