更新符号可识别的值的值，并且仅使用UserDefault缓存此值

Question

我有2个结构可编码： student 和 adress （与学生链接）

在我的应用程序上，我从firebase rtdb获取数据，然后我将其存储在UserDefault上 假设学生更改了他的电子邮件，我只想通过更新的电子邮件更新存储的UserDefault。

当我要存储它时，我需要指定所有其他数据（名称，adress，dob ...），或者我只能在不指定其他数据的情况下更新/存储电子邮件？

struct Adress : Codable, Identifiable {
    var id: String { Student_UID }
    var Student_UID: String
    var Student_Street: String
    var Student_Country: String
    var Student_City: String
    
    enum CodingKeys: String, CodingKey  {
        case Student_UID = "Adress_Student_UID"
        case Student_Street = "Student_Street"
        case Student_Country = "Student_Country"
        case Student_City = "Student_City"
        
    }
 
}

struct Student_Profile_Data:Codable, Identifiable   {
    var id: String { Student_UID }
    
    var Student_UID: String
    var Student_firstName: String?
    var Student_username : String?
    var Student_Email : String?
    var Student_lastName: String
    var Student_Address: Adress?
    var Student_DOB: String?
    var Student_Studentpoints : Int?
 
    
    enum CodingKeys: String, CodingKey {
        case Student_UID = "Student_UID"
        case Student_firstName = "Student_firstName"
        case Student_username = "Student_username"
        case Student_Email = "Student_Email"
        case Student_lastName = "Student_lastName"
        case Student_Address = "Student_Address"
        case Student_DOB = "Student_DOB"
        case Student_Studentpoints = "Student_Studentpoints"
     
       
 
    }
    
     
}


The USERDEfault part:

 
 
 //READ
 NSLog("userdefault TEST READ")
 let defaults = UserDefaults.standard
 if let savedStudent = defaults.object(forKey: "SavedStudent") as? Data {
     let decoder = JSONDecoder()
 if let loadedStudent = try? decoder.decode(Student_Profile_Data.self, from: savedStudent) {
     NSLog("TEST PROFILE- username : \(loadedStudent.Student_username)")

 }}
 

//WRITE
let add1 = Adress(Student_UID: "", Student_Street: "", Student_Country: "", Student_City: "")
let stud = Student_Profile_Data(Student_firstName: "", Student_username: "Martin", Student_Email: "", Student_lastName: "", Student_Address: add1, Student_DOB: "", Student_Studentpoints: 0, Student_UID: "")
 let encoder = JSONEncoder()
 if let encoded = try? encoder.encode(stud) {
     let defaults = UserDefaults.standard
     defaults.set(encoded, forKey: "SavedStudent")
     NSLog("WRITE OK »)
 }


//UPDATE ONE (OR TWO) VALUES ?


 

Answer 1

如果您以这种方式将学生存储在userDefault中，那么更新它将涉及读取学生的三步过程，更新其值，然后将其写回。

// read
let defaults = UserDefaults.standard
let decoder = JSONDecoder()
var savedStudent = defaults.data(forKey: "SavedStudent").flatMap {
    try? decoder.decode(StudentProfileData.self, from: $0)
} ?? StudentProfileData(...) // some "empty" student to use when there is no previously saved student

// update
savedStudent.firstName = "John"

// write
let encoder = JSONEncoder()
if let encoded = try? encoder.encode(savedStudent) {
    defaults.set(encoded, forKey: "SavedStudent")
}

为了使其更加方便，您可以将其提取为一个函数：

func updateSavedStudent(updateBlock: (inout StudentProfileData) -> Void) {
    // read
    let defaults = UserDefaults.standard
    let decoder = JSONDecoder()
    var savedStudent = defaults.data(forKey: "SavedStudent").flatMap {
        try? decoder.decode(StudentProfileData.self, from: $0)
    } ?? StudentProfileData(...) // some "empty" student to use when there is no previously saved student

    // update
    updateBlock(&savedStudent)

    // write
    let encoder = JSONEncoder()
    if let encoded = try? encoder.encode(savedStudent) {
        defaults.set(encoded, forKey: "SavedStudent")
    }
}

// usage:
updateSavedStudent {
    $0.firstName = "John"
    $0.lastName = "Smith"
}

或者，为此保存的学生制作计算的属性，并将其放在某个地方的公用事业类中。请注意，这将对您更新的每个属性进行编码并解码学生一次。

static var savedStudent: StudentProfileData {
    get {
        let defaults = UserDefaults.standard
        let decoder = JSONDecoder()
        return defaults.data(forKey: "SavedStudent").flatMap {
            try? decoder.decode(StudentProfileData.self, from: $0)
        } ?? StudentProfileData(...) // some "empty" student to use when there is no previously saved student
    }
    set {
        let encoder = JSONEncoder()
        if let encoded = try? encoder.encode(newValue) {
            defaults.set(encoded, forKey: "SavedStudent")
        }
    }
}

// usage
savedStudent.firstName = "John"