Thank you for the update.
Please open a new thread and describe your current problem in detail. I'm trying to follow this one but I'm getting lost with the two overlapping user experiences.
If you would start from the beginning and precisely describe the problem you are currently having I'm sure we can find the correct solution.
If the problem is that the default filename is blank in the code, which is what the only code example has, then try binding it again and switching focus to another field before clicking OK. Sometimes a field value won't update properly until blurred.