ios - 如果/否则基于数组中对象的存在？

Question

如果我在数组中查找的 indexPath 处没有对象，我想触发 else 语句。

数组是

let exerciseSets = unsortedExerciseSets.sorted { ($0.setPosition < $1.setPosition) }

然后我使用let cellsSet =exerciseSets[indexPath.row]

当用户添加新单元格时，它可能在indexPath 上没有一个exerciseSet 来填充它(将一个新集合添加到现有的集合数组中)，因此我需要运行一个else语句来设置一个空白单元格，而不是尝试填充它并使我的应用程序崩溃。

但是，如果我使用 if let 那么我会收到此错误:

Initializer for conditional binding must have Optional type, not 'UserExerciseSet'

如果需要，这里是上下文的整个函数:

    func configure(_ cell: NewExerciseTableViewCell, at indexPath: IndexPath) {
    if self.userExercise != nil {
        print("RESTORING CELLS FOR THE EXISTING EXERCISE")
        let unsortedExerciseSets = self.userExercise?.exercisesets?.allObjects as! [UserExerciseSet]
        let exerciseSets = unsortedExerciseSets.sorted { ($0.setPosition < $1.setPosition) }

        if let cellsSet = exerciseSets[indexPath.row] { // this causes a creash when user adds new set to existing exercise as it cant populate, needs an else statement to add fresh cell
            cell.setNumber.text = String(cellsSet.setPosition)
            cell.repsPicker.selectRow(Int(cellsSet.setReps), inComponent: 0, animated: true)

            let localeIdentifier = Locale(identifier: UserDefaults.standard.object(forKey: "locale") as! String)
            let setWeight = cellsSet.setWeight as! Measurement<UnitMass>
            let formatter = MassFormatter()
            formatter.numberFormatter.locale = localeIdentifier
            formatter.numberFormatter.maximumFractionDigits = 2

            if localeIdentifier.usesMetricSystem {
                let kgWeight = setWeight.converted(to: .kilograms)
                let finalKgWeight = formatter.string(fromValue: kgWeight.value, unit: .kilogram)
                let NumericKgResult = finalKgWeight.trimmingCharacters(in: CharacterSet(charactersIn: "0123456789.").inverted)
                cell.userExerciseWeight.text = NumericKgResult
            } else {
                let lbsWeight = setWeight.converted(to: .pounds)
                let finalLbWeight = formatter.string(fromValue: lbsWeight.value, unit: .pound)
                let NumericLbResult = finalLbWeight.trimmingCharacters(in: CharacterSet(charactersIn: "0123456789.").inverted)
                cell.userExerciseWeight.text = NumericLbResult
            }

        } else {
            cell.setNumber.text = String((indexPath.row) + 1)
        }

Answer 1

你可以做这样疯狂的事情:

if let cellSet = (indexPath.row < exerciseSets.count ? exerciseSets[indexPath.row] : nil) {
    //
}

但这样做会更简单:

if indexPath.row < exerciseSets.count {
    let cellSet = exerciseSets[indexPath.row]
    ...
}