swift - 如何获取数组中枚举案例的索引

Question

我需要更新存储在 Array 中的 Enum 的关联值。如何在不知道其索引的情况下访问正确案例的单元格？

enum MessageCell {
    case from(String)
    case to(String)
    case subject(String)
    case body(String)
}

var cells = [MessageCell.from(""), MessageCell.to(""), MessageCell.subject(""), MessageCell.body("")]

let recipient = "John"

// Hardcoded element position, avoid this
cells[1] = .to(recipient)

// How to find the index of .to case
if let index = cells.index(where: ({ ... }) {
    cells[index] = .to(recipient)
}

Answer 1

使用if case 来测试闭包中的enum case .to，如果找到则返回true , 否则返回 false:

if let index = cells.index(where: { if case .to = $0 { return true }; return false }) {
    cells[index] = .to(recipient)
}

---

这是一个完整的例子:

enum MessageCell {
    case from(String)
    case to(String)
    case subject(String)
    case body(String)
}

var cells: [MessageCell] = [.from(""), .to(""), .subject(""), .body("")]

if let index = cells.index(where: { if case .to = $0 { return true }; return false }) {
    print(".to found at index \(index)")
}

输出:

.to found at index 1