I'm working on an iOS app that requires an @mention system in a UITextView, similar to those in apps like Twitter or Slack. Specifically, I need to:
Detect @ Symbol and Show Dropdown: When the user types "@", display a dropdown (UITableView or similar) below the cursor with a list of mentionable users, filtered as the user types.
Handle Selection: Insert the selected username as a styled mention (e.g., blue text).
Smart Backspace Behavior: Ensure backspace deletes an entire mention as a single unit when the cursor is at its end, and cancels the mention process if "@" is deleted.
I've implemented a solution using UITextViewDelegate textViewDidChange(_:) to detect "@", a UITableView for the dropdown, and NSAttributedString for styling mentions. For smart backspace, I track mention ranges and handle deletions accordingly. However, I’d like to know:
What is Apple’s recommended approach for implementing this behavior?
Are there any UIKit APIs that simplify this, for proving this experience like smart backspace or custom text interactions?
I’m using Swift/UIKit. Any insights, sample code, or WWDC sessions you’d recommend would be greatly appreciated!
Edit: I am adding the ViewController file to demonstrate the approach that I m using.
import UIKit
// MARK: - Dummy user model
struct MentionUser {
let id: String
let username: String
}
class ViewController: UIViewController, UITextViewDelegate, UITableViewDelegate, UITableViewDataSource {
// MARK: - UI Elements
private let textView = UITextView()
private let mentionTableView = UITableView()
// MARK: - Data
private var allUsers: [MentionUser] = [...]
private var filteredUsers: [MentionUser] = []
private var currentMentionRange: NSRange?
// MARK: - View Lifecycle
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .white
setupTextView() // to setup the UI
setupDropdown() // to setup the UI
}
// MARK: - UITextViewDelegate
func textViewDidChange(_ textView: UITextView) {
let cursorPosition = textView.selectedRange.location
let text = (textView.text as NSString).substring(to: cursorPosition)
if let atRange = text.range(of: "@[a-zA-Z0-9_]*$", options: .regularExpression) {
let nsRange = NSRange(atRange, in: text)
let query = (text as NSString).substring(with: nsRange).dropFirst()
currentMentionRange = nsRange
filteredUsers = allUsers.filter {
$0.username.lowercased().hasPrefix(query.lowercased())
}
mentionTableView.reloadData()
showMentionDropdown()
} else {
hideMentionDropdown()
currentMentionRange = nil
}
}
func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
if text.isEmpty, let attributedText = textView.attributedText {
if range.location == 0 { return true }
let attr = attributedText.attributes(at: range.location - 1, effectiveRange: nil)
if let _ = attr[.mentionUserId] {
let fullRange = (attributedText.string as NSString).rangeOfMentionAt(location: range.location - 1)
let mutable = NSMutableAttributedString(attributedString: attributedText)
mutable.deleteCharacters(in: fullRange)
textView.attributedText = mutable
textView.selectedRange = NSRange(location: fullRange.location, length: 0)
textView.typingAttributes = [
.font: textView.font ?? UIFont.systemFont(ofSize: 16),
.foregroundColor: UIColor.label
]
return false
}
}
return true
}
// MARK: - Dropdown Visibility
private func showMentionDropdown() {
guard let selectedTextRange = textView.selectedTextRange else { return }
mentionTableView.isHidden = false
}
private func hideMentionDropdown() {
mentionTableView.isHidden = true
}
// MARK: - UITableViewDataSource
func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return filteredUsers.count
}
func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCell(withIdentifier: "cell", for: indexPath)
cell.textLabel?.text = "@\(filteredUsers[indexPath.row].username)"
return cell
}
// MARK: - UITableViewDelegate
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
insertMention(filteredUsers[indexPath.row])
}
// MARK: - Mention Insertion
private func insertMention(_ user: MentionUser) {
guard let range = currentMentionRange else { return }
let mentionText = "\(user.username)"
let mentionAttributes: [NSAttributedString.Key: Any] = [
.foregroundColor: UIColor.systemBlue,
.mentionUserId: user.id
]
let mentionAttrString = NSAttributedString(string: mentionText, attributes: mentionAttributes)
let mutable = NSMutableAttributedString(attributedString: textView.attributedText)
mutable.replaceCharacters(in: range, with: mentionAttrString)
let spaceAttr = NSAttributedString(string: " ", attributes: textView.typingAttributes)
mutable.insert(spaceAttr, at: range.location + mentionText.count)
textView.attributedText = mutable
textView.selectedRange = NSRange(location: range.location + mentionText.count + 1, length: 0)
textView.typingAttributes = [
.font: textView.font ?? UIFont.systemFont(ofSize: 16),
.foregroundColor: UIColor.label
]
hideMentionDropdown()
}
}
// MARK: - Custom Attributed Key
extension NSAttributedString.Key {
static let mentionUserId = NSAttributedString.Key("mentionUserId")
}
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