Class 数组对象值在 json 序列化后总是 return nil

Question

我创建了一个名为 "GetDataFromURL" 的函数，它的主要任务是从 URL 中获取数据并将其存储到本地 Class 数组对象中。使用 URlSession.shared.dataTask 功能我将数据接收到数据格式，然后通过使用 jsonserialization.jsonObject 方法我进入 json 格式。响应是字典格式，因此存储到临时 class 对象中，最后它将附加到全局 class 数组对象。此函数在 Page 调用 "View Load" 方法时调用。在函数内，它将显示所有数据，但每次我在块外显示时得到 nil 数组对象。

public class Modelclass : NSObject {

var id :Int!
var albumId : Int!
var title : String!
var url : String!
var thumbnailUrl : string! 

}

这是 Class 文件，下面是 viewcontroller 文件：

var temp:[ModelClass]? 

override func viewDidLoad() {

super.viewDidLoad()
self.temp = [ModelClass]()
dispatchQueue.main.async{
    self.GetDataFromURL()
}

print(self.temp,"Tesing print")
}



  func GetDatafromURL() {

  if let url = URL(string : 
  "https://jsonplaceholder.typicode.com/photos"){
   URLSession.shared.dataTask(with: url){(data,response,error) in
    if error != nil {
        print(error)
        return
    }
    do{
        let jsonresponse = try jsonserialization.jsonObject(with:data! , 
        options: .mutablecontainers)
        for dictionary in jsonresponse as! [[String:AnyObject]]
        {
            var test = ModelClass()
            test.title = dictionary["title"] as? String
            test.albumId = dictionary["albumId"] as? Int
            test.id = dictionary["id"] as? Int
            test.thumbnailUrl = dictionary["thumbnailUrl"] as? String
            test.url = dictionary["url"] as? String
            self.temp?.append(test)
        }

    }
    catch let jsonerror{
        print(jsonerror)
    }
 }.resume()
}
}

它向我展示了“optional([]) Tesing print”作为Output.and，同时在 do Block 中打印临时对象，它将显示所有数据。

Answer 1

// 添加这个 var dispatchgroup = DispatchGroup() //

var temp: [Modelclass] = []

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view.


    self.GetDatafromURL()

    //Add this
    dispatchgroup.notify(queue: .main){
         print("temp data : \(self.temp.count)")
    }

}



  func GetDatafromURL() {

    //add this
    dispatchgroup.enter()
    //

  if let url = URL(string :
  "https://jsonplaceholder.typicode.com/photos"){
   URLSession.shared.dataTask(with: url){(data,response,error) in
    if error != nil {
        print(error)
        return
    }
    do{


        let jsonresponse = try JSONSerialization.jsonObject(with: data!, options: .mutableContainers)

        for dictionary in jsonresponse as! [[String:AnyObject]]
        {
            var test = Modelclass()
            test.title = dictionary["title"] as? String
            test.albumId = dictionary["albumId"] as? Int
            test.id = dictionary["id"] as? Int
            test.thumbnailUrl = dictionary["thumbnailUrl"] as? String
            test.url = dictionary["url"] as? String
            self.temp.append(test)
        }

          //add this
        self.dispatchgroup.leave()
        //


    }
    catch let jsonerror{
        print(jsonerror)
    }
 }.resume()
}

}

Answer 2

这是目标 c 的版本，

   @property (strong,nonatomic) NSMutableArray<UserModel *> *jsonarray ;
   @end

   @implementation ViewController

   dispatch_group_t serviceGroup;
   NSMutableDictionary *result ;


  - (void)viewDidLoad {
   [super viewDidLoad];
   // Do any additional setup after loading the view, typically from a nib.

    result = [[NSMutableDictionary alloc]init];
    self.tableView.delegate = self;
    self.tableView.dataSource = self;

     UINib *nib = [UINib nibWithNibName:@"TableViewCell" bundle:nil];
    [self.tableView registerNib:nib forCellReuseIdentifier:@"TableViewCell"];
    serviceGroup = dispatch_group_create();


    _jsonarray = [[NSMutableArray alloc]init];

// \ [用户数据 GetDatafromUrl:@"https://jsonplaceholder.typicode.com/users"];

    [self GEtDataFromurl:@"https://jsonplaceholder.typicode.com/users"];
    }



 -(void)GEtDataFromurl:(NSString *) urlstr{

 dispatch_group_enter(serviceGroup);
[[NSURLSession.sharedSession dataTaskWithURL:[NSURL URLWithString:urlstr] completionHandler:^(NSData *_Nullable data,NSURLResponse *_Nullable response, NSError *_error){
    NSError *err;
    NSArray *json = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingAllowFragments error:&err];
    if(err){
        NSLog(@"Falied to serialization.. ");
        return;
    }

    for (NSDictionary *UserDir in json){
        NSString *Id = UserDir[@"id"] ;
        NSString *name = UserDir[@"name"] ;
        NSString *username = UserDir[@"username"];
        NSString *email = UserDir[@"email"];
        NSString *phone = UserDir[@"phone"];
        NSString *website = UserDir[@"website"];

        struct company *company = CFBridgingRetain(UserDir[@"company"]);
        struct address *address = CFBridgingRetain(UserDir[@"address"]);

        UserModel *model = UserModel.new;
        model.Id =  [Id intValue];
        model.name = name;
        model.address = address;
        model.username = username;
        model.email  = email;
        model.phone = phone;
        model.website = website;
        model.company = company;
        NSLog(@"%@", model.name);
        [_jsonarray addObject:model];

    }
            dispatch_group_leave(serviceGroup);
}]resume];

dispatch_group_notify(serviceGroup,dispatch_get_main_queue(),^{


    NSLog(@" outside user class :  %@", _jsonarray);

    [self.tableView reloadData];
});

}

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView{ return1个； }

-(UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

TableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"TableViewCell" forIndexPath:indexPath];
if(cell == nil){
    NSArray *obj = [[NSBundle mainBundle] loadNibNamed:@"TableViewCell" owner:self options:nil];
    cell = [obj objectAtIndex:0];
}
UserModel *model = _jsonarray[indexPath.row];
cell.displaylabel.text = model.username;

return  cell;

}

- (NSInteger)tableView:(nonnull UITableView *)tableView numberOfRowsInSection:                (NSInteger)section {
 return _jsonarray.count;

}

@end

Class 数组对象值在 json 序列化后总是 return nil

Class array object value always return nil after json serialization

json

ios

nsjsonserialization

nsurlsession

swift