如何处理 NIL 值变量

Question

我有如下模型。

struc Info: Decodable {
var firstName: String?
var lastName: String?
}

在表格视图单元格中显示时，我正在做的事情如下。

personName.text = "(personArray[indexPath.row].firstName!) (personArray[indexPath.row].lastName!)"

现在，如果我有以下格式的数据，应用程序就会崩溃

[
{
"firstName" : "F 1",
"lastName" : "L 1"
},
{
"firstName" : "F 2"
},
{
"lastName" : "L 3"
}
]

该应用程序崩溃说姓氏为零

---

解决方案 1

此检查的解决方案为 nil 然后显示名称，但是我不想在运行时进行检查，因为我必须检查所有变量(考虑到我有 25 个变量的模型(。以下是我本可以做的。

var firstName = ""
if (personArray[indexPath.row].firstName == nil) {
firstName = ""
} else {
firstName = personArray[indexPath.row].firstName!
}
var lastName = ""
if (personArray[indexPath.row].lastName == nil) {
lastName = ""
} else {
lastName = personArray[indexPath.row].lastName!
}
personName.text = "(firstName) (lastName)"

解决方案 2

我可以在模型本身中进行更新，如下所示。

struc Info: Decodable {
var firstName: String?
var lastName: String?
var firstName2 : String? {
get {
if (self.firstName==nil) {
return ""
}
return firstName
}
var lastName2 : String? {
get {
if (self.lastName==nil) {
return ""
}
return lastName
}
}
personName.text = "(personArray[indexPath.row].firstName2!) (personArray[indexPath.row].lastName2!)"

但是我对此也有问题。这样，我必须再次创建 N 个变量。

如果 Web 服务中缺少该变量，是否有任何其他替代方法可以分配默认值？

Answer 1

我会推荐以下两个选项之一：

1. 将计算属性添加到结构以确定显示名称。
2. 手动解码，提供默认值。(如果需要，还可以添加显示名称属性(

就个人而言，我喜欢选项 1。我认为它是最紧凑的，也是最容易维护的。

选项 1 示例：

struct Info1: Decodable {
var firstName: String?
var lastName: String?
var displayName: String {
return [self.firstName, self.lastName]
.compactMap { $0 } // Ignore 'nil'
.joined(separator: " ") // Combine with a space
}
}
print(Info1(firstName: "John", lastName: "Smith").displayName)
// Output: "John Smith"
print(Info1(firstName: "John", lastName: nil).displayName)
// Output: "John"
print(Info1(firstName: nil, lastName: "Smith").displayName)
// Output: "Smith"
print(Info1(firstName: nil, lastName: nil).displayName)
// Output: ""

选项 2 示例：

struct Info2: Decodable {
var firstName: String
var lastName: String
enum CodingKeys: String, CodingKey {
case firstName, lastName
}
init(from decoder: Decoder) throws {
let container = try decoder.container(keyedBy: CodingKeys.self)
self.firstName = try container.decodeIfPresent(String.self, forKey: .firstName) ?? ""
self.lastName = try container.decodeIfPresent(String.self, forKey: .lastName) ?? ""
}
// Optional:
var displayName: String {
return [self.firstName, self.lastName]
.compactMap { $0.isEmpty ? nil : $0 } // Ignore empty strings
.joined(separator: " ") // Combine with a space
}
// TEST:
init(from dict: [String: Any]) {
let data = try! JSONSerialization.data(withJSONObject: dict, options: .prettyPrinted)
self = try! JSONDecoder().decode(Info2.self, from: data)
}
}
print(Info2(from: ["firstName": "John", "lastName": "Smith"]).displayName)
// Output: "John Smith"
print(Info2(from: ["lastName": "Smith"]).displayName)
// Output: "Smith"
print(Info2(from: ["firstName": "John"]).displayName)
// Output: "John"
print(Info2(from: [String: Any]()).displayName)
// Output: ""