How to avoid repeating a condition in methods that use it differently?

Question

Let's say I have an app that displays details for a person. Each person can have zero or more phone numbers and zero or more notes attached to it. Thus, I have a Core Data entity Person with one-to-many relationships to the Phone entity and the Note entity. I want to show these in a UITableView, where there is one section "phones" and one section "notes".

So, numberOfRowsInSection would look like that:

func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
 switch section {
 case 0: // Phones
 if self.person.phones.count > 0 {
 return self.person.phones.count
 } else {
 return 1 // We want a different cell to display "no phones"
 }
 case 1: // Notes
 if self.person.notes.count > 0 {
 return self.person.notes.count
 } else {
 return 1 // We want a different cell to display "no notes"
 default:
 return 0
 }
}

And cellForRowAt would look like this:

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
 switch indexPath.section {
 case 0:
 if self.person.phones.count > 0 {
 return UITableViewCell.init(style: .default, reuseIdentifier: "PhoneNumberCell")
 } else {
 return UITableViewCell.init(style: .default, reuseIdentifier: "NoPhoneNumbersCell")
 }
 case 1:
 if self.person.notes.count > 0 {
 return UITableViewCell.init(style: .default, reuseIdentifier: "NoteCell")
 } else {
 return UITableViewCell.init(style: .default, reuseIdentifier: "NoNotesCell")
 }
 default:
 return UITableViewCell.init(style: .default, reuseIdentifier: "default")
 }
}

And then, you can guess already, the same code would repeat for willDisplay:

func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
 switch indexPath.section {
 case 0:
 if self.person.phones.count > 0 {
 // Configure Phone Cell
 } else {
 // Configure No Phones Cell
 }
 case 1:
 if self.person.notes.count > 0 {
 // Configure Note Cell
 } else {
 // Configure No Notes Cell
 }
 default: break
 }
}

Same would apply for didSelectRowAt (and other delegate/datasource methods) but I won't copy more here.

What I want to do is get rid of this long and repeating switch with if..else statement but the problem is that in some cases I use it to return a number, in others a String and in others to just configure a cell.

Does anyone have an idea or pattern to recommend for this case?

• gnat: Possible duplicate of Should I repeat condition checking code or put it in a function?
• gnat: see also: How to avoid spaghetti code when I have a lot of conditions?
• amon: This looks like an excellent opportunity for the "Replace conditionals with polymorphism" refactoring technique. Note that you're essentially managing 5 different table views, each could be their own class.

Answer 1

Here's the kind of data source I would like to see for your example:

func numberOfSections(in tableView: UITableView) -> Int {
 return sections.count
}
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
 return sections[section].itemCount
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
 return sections[indexPath.section].cell(forRow: indexPath.row)
}

To make the above work, you will need a Section Protocol:

protocol Section {
 var itemCount: Int { get }
 var cell(forRow row: Int) -> UITableViewCell 
}

... as well as a PhoneNumberSection and NoteSection that both implement that protocol.

• Daniel T.: This is essentially what @amon was suggesting in his comment.