Swift 代码问题 - 试图将对象从 NSMutableArray 中转换为自定义对象
Swift code problem - trying to cast objects out from a NSMutableArray as a custom object
这是我的代码,它无法执行,如下所述。
我正在尝试将一个对象转换为我的名为 UserData 的自定义数据类型。
我遇到的第一个问题是不明白如何正确地从数组中获取值
其次,我似乎无法将对象转换为我需要的类型 UserData。我做错了什么?
func parseJSON(_ data:Data) {
var jsonResult = NSArray()
var users = NSMutableArray();
do{
jsonResult = try JSONSerialization.jsonObject(with: data, options:JSONSerialization.ReadingOptions.allowFragments) as! NSArray
} catch let error as NSError {
print(error)
}
var jsonElement = NSDictionary()
for i in 0 ..< jsonResult.count {
print("loop count :", i );
jsonElement = jsonResult[i] as! NSDictionary
let user = UserData()
//the following insures none of the JsonElement values are nil through optional binding
if let UserID = jsonElement["Userid"] as? String,
let firstName = jsonElement["First_Name"] as? String,
let lastName = jsonElement["Last_Name"] as? String,
let userSessionID = jsonElement["Session_ID"] as? String
{
user.UserID = UserID
user.FirstName = firstName
user.LastName = lastName
user.UserSessionID = userSessionID
print("users firstName:", user.FirstName ?? "blank");
}
users.add(user)
}
print("users size:", users.count); // this shows 2
// So i know I have data loaded... BUT when i try and
// get it then it all goes to heck. See below
// NOT SURE what I am doing here...
// Thought it was java like where I could just get a
// item from the NSMutableArray using an index value
// then cast it as my UserData object
// and print the output... but this does not work
// Why is this so hard??
let userDataVal = users.index(of: 0) as! UserData;
print("firstName:", userDataVal.FirstName);
}
下面是我将如何编写此函数。一些评论
- 没有使用 NS...类,我使用原生数组和字典
- 如果 JSONSerialization.jsonObject 产生错误则函数退出
- 局部变量的定义尽可能接近它们的使用位置
- 为您的
UserData
struct/class 创建一个将值作为参数的初始化方法,这样您就可以执行 let user = UserData(userId: UserId, firstName:...
。
- 以第一个小写字符命名局部变量和属性,这样更容易阅读代码
func parseJSON(_ data:Data) {
var jsonResult: [[String: Any]]?
do {
jsonResult = try JSONSerialization.jsonObject(with: data, options:JSONSerialization.ReadingOptions.allowFragments) as? [[String: Any]]
} catch let error as NSError {
print(error)
return
}
guard let result = jsonResult else {
return
}
var users = [UserData]()
for jsonElement in result {
if let UserID = jsonElement["Userid"] as? String,
let firstName = jsonElement["First_Name"] as? String,
let lastName = jsonElement["Last_Name"] as? String,
let userSessionID = jsonElement["Session_ID"] as? String
{
var user = UserData()
user.UserID = UserID
user.FirstName = firstName
user.LastName = lastName
user.UserSessionID = userSessionID
users.append(user)
}
}
for user in users {
print("firstName:", user.FirstName);
}
}
更好的方法是使用 JSONDecoder() 而不是 JSONSerailizer。尝试使用以下代码。
struct User: Codable {
var userId, firstName, lastName, userSessionId: String
enum CodingKeys: String, CodingKey {
case userId = "Userid"
case firstName = "First_Name"
case lastName = "Last_Name"
case userSessionId = "Session_ID"
}
}
func parseJSON(_ data: Data) {
do {
let users = try JSONDecoder().decode([User].self, from: data)
users.forEach { user in
print("users first name:", user.firstName)
}
} catch {
print(error.localizedDescription)
}
}
这是我的代码,它无法执行,如下所述。
我正在尝试将一个对象转换为我的名为 UserData 的自定义数据类型。 我遇到的第一个问题是不明白如何正确地从数组中获取值 其次,我似乎无法将对象转换为我需要的类型 UserData。我做错了什么?
func parseJSON(_ data:Data) {
var jsonResult = NSArray()
var users = NSMutableArray();
do{
jsonResult = try JSONSerialization.jsonObject(with: data, options:JSONSerialization.ReadingOptions.allowFragments) as! NSArray
} catch let error as NSError {
print(error)
}
var jsonElement = NSDictionary()
for i in 0 ..< jsonResult.count {
print("loop count :", i );
jsonElement = jsonResult[i] as! NSDictionary
let user = UserData()
//the following insures none of the JsonElement values are nil through optional binding
if let UserID = jsonElement["Userid"] as? String,
let firstName = jsonElement["First_Name"] as? String,
let lastName = jsonElement["Last_Name"] as? String,
let userSessionID = jsonElement["Session_ID"] as? String
{
user.UserID = UserID
user.FirstName = firstName
user.LastName = lastName
user.UserSessionID = userSessionID
print("users firstName:", user.FirstName ?? "blank");
}
users.add(user)
}
print("users size:", users.count); // this shows 2
// So i know I have data loaded... BUT when i try and
// get it then it all goes to heck. See below
// NOT SURE what I am doing here...
// Thought it was java like where I could just get a
// item from the NSMutableArray using an index value
// then cast it as my UserData object
// and print the output... but this does not work
// Why is this so hard??
let userDataVal = users.index(of: 0) as! UserData;
print("firstName:", userDataVal.FirstName);
}
下面是我将如何编写此函数。一些评论
- 没有使用 NS...类,我使用原生数组和字典
- 如果 JSONSerialization.jsonObject 产生错误则函数退出
- 局部变量的定义尽可能接近它们的使用位置
- 为您的
UserData
struct/class 创建一个将值作为参数的初始化方法,这样您就可以执行let user = UserData(userId: UserId, firstName:...
。 - 以第一个小写字符命名局部变量和属性,这样更容易阅读代码
func parseJSON(_ data:Data) {
var jsonResult: [[String: Any]]?
do {
jsonResult = try JSONSerialization.jsonObject(with: data, options:JSONSerialization.ReadingOptions.allowFragments) as? [[String: Any]]
} catch let error as NSError {
print(error)
return
}
guard let result = jsonResult else {
return
}
var users = [UserData]()
for jsonElement in result {
if let UserID = jsonElement["Userid"] as? String,
let firstName = jsonElement["First_Name"] as? String,
let lastName = jsonElement["Last_Name"] as? String,
let userSessionID = jsonElement["Session_ID"] as? String
{
var user = UserData()
user.UserID = UserID
user.FirstName = firstName
user.LastName = lastName
user.UserSessionID = userSessionID
users.append(user)
}
}
for user in users {
print("firstName:", user.FirstName);
}
}
更好的方法是使用 JSONDecoder() 而不是 JSONSerailizer。尝试使用以下代码。
struct User: Codable {
var userId, firstName, lastName, userSessionId: String
enum CodingKeys: String, CodingKey {
case userId = "Userid"
case firstName = "First_Name"
case lastName = "Last_Name"
case userSessionId = "Session_ID"
}
}
func parseJSON(_ data: Data) {
do {
let users = try JSONDecoder().decode([User].self, from: data)
users.forEach { user in
print("users first name:", user.firstName)
}
} catch {
print(error.localizedDescription)
}
}