Question

If i am using Android 2.2 and call File.list() method in BookGenerator.java, then pages and chapters come in exact sequence, but whenever I execute on Android 4.0 it gives me reverse pages list or reverse pages order.

Is there a compatibility issue between 2.2 and 4.0?

Answer 1

You shouldn’t rely on listFiles() for an ordered list of the pages:

http://docs.oracle.com/javase/1.4.2/docs/api/java/io/File.html#listFiles()

“There is no guarantee that the name strings in the resulting array will appear in any specific order;”

You have to create your own ordering system, based on file name or lastModified or file’s size. You can either use a Comparator < File > or Comparator < String > for sorting the files in a SortedSet, or as mentionned earlier, create an own class for the items to sort that implements Comparable. I would suggest the first solution as it’s a bit stupid to wrap the File or String class into an other one just for this functionality.

An example with a lot of memory overhead:

TreeSet<File> pages = new TreeSet<File>(new Comparator<File>(){
   public int compare(File first, File second) {
      return first.getName().compareTo(second.getName());
   }
});

for (File file : allFiles) {
   pages.add(file());
}

allFiles = pages.toArray();

If you want a more efficient one, you have to implement your own method for sorting an array in its place.