Swift 如何获取数组中枚举大小写的索引
我需要更新存储在Swift 如何获取数组中枚举大小写的索引,swift,enums,Swift,Enums,我需要更新存储在数组中的Enum的关联值。如何在不知道其索引的情况下访问适当案例的单元格 enum MessageCell { case from(String) case to(String) case subject(String) case body(String) } var cells = [MessageCell.from(""), MessageCell.to(""), MessageCell.subject(""), MessageCell.bo
数组中的Enum
的关联值。如何在不知道其索引的情况下访问适当案例的单元格
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)
}
试试这个:
if let index = cells.index(where: { (messageCell) -> Bool in
switch messageCell
{
case .to(let x):
return x == recipient ? true : false
default:
return false
}
})
{
cells[index] = .to(recipient)
}
下面是一个简化的演示,演示如何解决此问题,以便了解其工作原理:
var arr = ["a", "b"] // a, b
if let index = arr.index(where: { $0 == "a" }) {
arr[index] = "c"
}
print(arr) // c, b
就你而言:
if let index = cells.index(where: { if case .to = $0 { return true } else { return false } }) {
cells[index] = .to(recipient)
}
使用if case
测试闭包中的枚举案例。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)
}
下面是一个完整的示例:
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:
作为使用索引(其中:)
的替代方法,您可以将模式匹配与for
循环一起使用,以迭代与给定情况匹配的元素的索引,然后在第一次匹配时简单地中断
:
var cells: [MessageCell] = [.from(""), .to(""), .subject(""), .to("")]
let recipient = "John"
for case let (offset, .to) in cells.enumerated() {
cells[offset] = .to(recipient)
break
}
print(cells)
// [MessageCell.from(""), MessageCell.to("John"),
// MessageCell.subject(""), MessageCell.to("")]
看看这个,它吸吮关闭必须是如此复杂;查阅
var cells: [MessageCell] = [.from(""), .to(""), .subject(""), .to("")]
let recipient = "John"
for case let (offset, .to) in cells.enumerated() {
cells[offset] = .to(recipient)
break
}
print(cells)
// [MessageCell.from(""), MessageCell.to("John"),
// MessageCell.subject(""), MessageCell.to("")]