testFutures.dart

#import("dart:io"); 
main(){ 
  int sum = 0; 
  DirectoryLister lister = new Directory("c:\\dropbox").list(true); 
  var filesProcessed = new List<Future>();
  lister.onError = (e) { throw e; }; 
  lister.onFile = (String file) { 
    // print("File: $file"); 
    // Please ignore the length() vs lengthSync(), because my 
    // actual use case is a longer IO operation, e.g. DB call. 
    Future f = new File(file).length(); 
    filesProcessed.add(f);
    f.then((int c) { 
      sum += c; 
      //print(" - sum: $sum ($file)"); 
    }); 
  }; 
  lister.onDone = (bool success) { 
    Futures.wait(filesProcessed).then((_) {
      print("Final sum: $sum");    
    });
  }; 
}