Add an Index in TableView

I want to create a tableView which is about a friend list. If there is a large mass of data. I’d like to have an index that sort list by the first letter in the tableView.

let names = ["Aaron", "Adam", "Adolph", "Bert", "Carey", "Colin", "Eden", "Edmund", "Elmo", "Gary", "Giles", "Harvie", "Hiram", "Jeff", "Jeremy", "Jo", "Kelly", "Nick", "Neil", "Noah", "Perry", "Philip", "Sampson", "Scott", "Sidney", "Simon", "Tim", "Todd", "Tracy", "Troy", "Vincent", "Walker", "Wayne", "Wythe", "Yasir", "York", "Zavier"]

First of all, I declare an empty dictionary named nameDict for sorting name list, an empty dictionary named nameSectionTitles for the section titles, and a constant named nameIndexTitles for the index.

var nameDict = [String: [String]]()
var nameSectionTitles = [String]()
let nameIndexTitles = ["A", "B", "C","D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"]

There are functions to deal with the number of sections and section titles in tableView.

override func numberOfSections(in tableView: UITableView) -> Int {
return nameSectionTitles.count
}
override func tableView(_ tableView: UITableView, titleForHeaderInSection section: Int) -> String? {
return nameSectionTitles[section]
}

Set the index titles and fix the section index doesn’t exist any item.

override func sectionIndexTitles(for tableView: UITableView) -> [String]? {
return nameIndexTitles
}
override func tableView(_ tableView: UITableView, sectionForSectionIndexTitle title: String, at index: Int) -> Int {
guard let index = nameSectionTitles.firstIndex(of: title) else {
return -1
}
return index
}

Set numbers of rows in the section

override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
let firstLetter = nameSectionTitles[section]
guard let nameValues = namesDict[firstLetter] else {
return 0
}
return nameValues.count
}

Set the cell

override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: “Cell”, for: indexPath)
// Configure the cell
let firstLetter = nameSectionTitles[indexPath.section]
if let nameValues = namesDict[firstLetter] {
cell.textLabel?.text = nameValues[indexPath.row]
}
return cell
}

This is a very important part, that is about how to make the dictionary of the names. After collected key in the dictionary, sort them by the last two lines code.

func createNameDict() {
for name in names {
let firstLetter = String(name.prefix(1))
if var nameValues = namesDict[firstLetter]{
nameValues.append(name)
namesDict[firstLetter] = nameValues
} else {
namesDict[firstLetter] = [name]
}
nameSectionTitles = [String](namesDict.keys)
nameSectionTitles = nameSectionTitles.sorted(by: {$0 < $1})
}
}

There is a skill about debugging. Print the variables in the function. It'd let me know how the function works and how the variable change in a particular place.

let firstLetter = String(name.prefix(1))
print(namesDict)
if var nameValues = namesDict[firstLetter] {
print(“in if”)
print(namesDict)
nameValues.append(name)
namesDict[firstLetter] = nameValues
print(“in end if”)
print(namesDict)
} else {
print(“in else”)
print(namesDict)
namesDict[firstLetter] = [name]
print(“in end else”)
print(namesDict)
}

Feel free to visit my Github for further details.