title: How to append data to NSKeyedArchive?
body: <p>I'm reading a file like so:</p>
  
  <pre><code>NSData *data = [NSData dataWithContentsOfFile:myPath];
  
  NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:data];
  
  
  NSData *imgData = [unarchiver decodeObjectForKey:@"myimage"];
  
  if (imgData != nil) {
      self.image = [[NSImage alloc]initWithData:imgData];
  }else{
      self.image = nil;
  }
  
  [unarchiver finishDecoding];
  [unarchiver release];
  </code></pre>
  
  <p>What I'd like to do is to append image data for key @"myimage" to the same file if it doesn't exist.</p>
  
  <p>How to go about it?</p>