Swift: Creating a csv file in Documents Directory

I am creating a registration form application. The registration form data will be saved in a CSV file. I need to create a csv file in the documents directory and be able to write to it. I'm pretty new to Swift so I'm having a bit of trouble. This is what I've got so far.

var fileManager = NSFileManager.defaultManager()
var fileHandle: NSFileHandle

@IBAction func submitForm(sender: AnyObject) {
    mySingleton.filename = mySingleton.filename + ".csv"
    let documentsPath = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)[0]
    let filePath = documentsPath + mySingleton.filename

    if !fileManager.fileExistsAtPath(mySingleton.filename) {
        fileManager.createFileAtPath(filePath, contents: nil, attributes: nil)
        fileHandle = ...
    }

}

Obviously the code I'm having trouble with is the FileHandle which is what allows to to modify the file. In objective-c it would look something like this:

fileHandle = [NSFileHandle fileHandleForUpdatingAtPath:event];

Then obviously if I wanted to write to the file I could do something like this:

[fileHandle seekToEndOfFile];
[fileHandle writeData:[formData dataUsingEncoding:NSUTF8StringEncoding]];
[fileHandle closeFile];

So I'm really only struggling with that one part. Thanks for the help!

In Swift, fileHandleForUpdatingAtPath has become an initializer of NSFileHandle, adopting the Swift naming convention of avoiding repetition and taking the end of the Objective-C method name, making it the parameter name:

let fileHandle = NSFileHandle(forUpdatingAtPath: yourPath)