How to add data for NSOutputStream?

Answer 1

My question is where can I add code like "sendStream = ..."?

You're already assigning sendStream with the getStreamsToHost:port:inputStream:outputStream: message. That method returns the two streams by reference.

… how to convert the imageData to NSOutputStream's instance?

You don't need to convert the data to a stream, you need to tell a stream to write the data.

Try NSOutputStream's write:maxLength: method. You'll need to pass the bytes and length from the data object.