Proper cellForRowAtIndexPath cell return in Swift

Question

So I have started creating a UITableView with multiple prototype cells. I currently have the below code setup, which works fine

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {

    var cell: UITableViewCell?

    if indexPath.row == tableView.numberOfRowsInSection(0) - 1 {
        cell = tableView.dequeueReusableCellWithIdentifier("AddSetCell")
    } else {
        cell = tableView.dequeueReusableCellWithIdentifier("SetCell") as! SetTableViewCell
    }

    return cell!
}

I have learned to avoid using ! as much as possible when dealing with optionals. However, I also don't like creating an if let statement a thousand times. In theory, cell should never be nil because my code only allows cell to be one of the identifiers above. However it still makes me nervous in terms of bad practice.

If I do var cell = UITableViewCell, I have to unwrap both of the calls to dequeueReusableCellWithIdentifier or XCode gets mad at me.

Which is the best approach for this case?

Answer 1

First note that

func dequeueReusableCellWithIdentifier(identifier: String, forIndexPath indexPath: NSIndexPath) -> UITableViewCell

is preferred over

func dequeueReusableCellWithIdentifier(identifier: String) -> UITableViewCell?

because – according to the documentation –

This method uses the index path to perform additional configuration based on the cell’s position in the table view.

and because it returns a non-optional UITableViewCell.

If you just want to return one of the two possible prototype cells then you don't need to cast at all.

But there is no need to make cell an optional. You can even declare it as a constant, this allows the compiler to verify that it is assigned a value exactly once on each code path.

let cell: UITableViewCell
if condition {
    cell = tableView.dequeueReusableCellWithIdentifier("AddSetCell", forIndexPath: indexPath)
} else {
    cell = tableView.dequeueReusableCellWithIdentifier("SetCell", forIndexPath: indexPath)
}
// ... set up common properties ...
return cell

If you want to assign specific properties to the different cell types then you need to cast to the respective type. Since you define the custom class SetTableViewCell for the prototype cell with identifier "SetCell" in the Storyboard,

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

is guaranteed to return an instance of SetTableViewCell, either by re-using a cell or by instantiating a new one from the prototype. This is one of the legitimate use-cases of the forced cast operator as!. Or to put it differently: The cast can only fail if you did not define the prototype cell correctly. That would be a programming error and should be detected early.

let cell: UITableViewCell
if condition {
    let aCell = tableView.dequeueReusableCellWithIdentifier("AddSetCell") as! AddTableViewCell
    // ... set up specific properties ...
    cell = aCell
} else {
    let sCell = tableView.dequeueReusableCellWithIdentifier("SetCell") as! SetTableViewCell
    // ... set up specific properties ...
    cell = sCell
}
// ... set up common properties ...
return cell

or alternatively with "early return":

if condition {
    let aCell = tableView.dequeueReusableCellWithIdentifier("AddSetCell") as! AddTableViewCell
    // ... set up properties ...
    return aCell
} else {
    let sCell = tableView.dequeueReusableCellWithIdentifier("SetCell") as! SetTableViewCell
    // ... set up properties ...
    return sCell
}

that is a matter of personal choice.

Finally, if you write your condition as

indexPath.row == tableView.numberOfRowsInSection(indexPath.section) - 1

then it will work for all sections, not only the first one.