UITableViewCell detailTextLabel not showing up

You've registered the UITableViewCell

theTableView.registerClass(UITableViewCell.self,
 forCellReuseIdentifier: "reuseIdentifier")

This means that when you call

tableView.dequeueReusableCellWithIdentifier("reuseIdentifier", 
forIndexPath: indexPath)

one will be automatically created for you using the UITableViewCellStyleDefault style.

Because you want a custom style you need to do a few things:

Remove

theTableView.registerClass(UITableViewCell.self, 
forCellReuseIdentifier: "reuseIdentifier")

Replace

var cell = tableView.dequeueReusableCellWithIdentifier("reuseIdentifier", 
forIndexPath: indexPath)

with the following

var cell = tableView.dequeueReusableCellWithIdentifier("reuseIdentifier")
if cell == nil {
    cell = UITableViewCell(style: .Value1, reuseIdentifier: "reuseIdentifier")
}

What is happening here is dequeueReusableCellWithIdentifier will return nil if it can't dequeue a cell. You can then generate your own cell providing with the specified style.

If you are using Storyboard:

1. select a cell
2. go to attributes inspector
3. click style
4. choose Subtitle

I found that it's not enough to check if the cell is nil. I added this additional check:

var cell: UITableViewCell? = tableView.dequeueReusableCell(withIdentifier: cellReuseIdentifier, for: indexPath)
if cell == nil || cell?.detailTextLabel == nil {
    cell = UITableViewCell(style: .subtitle, reuseIdentifier: cellReuseIdentifier)
}