用JSON初始化自定义类返回nil

Question

我的代码中有这一行，

Country *country = [[Country alloc] initWithNSDictionary:jsonObject];

我在jsonObject中得到一个元素，但为什么国家为nil?

我在项目中有一个国家类文件，我已经通过这个创建了一个对象。

JSON响应:

{"geonames": [{
  "continent": "AS",
  "capital": "Nuova Delhi",
  "languages": "en-IN,hi,bn,te,mr,ta,ur,gu,kn,ml,or,pa,as,bh,sat,ks,ne,sd,kok,doi,mni,sit,sa,fr,lus,inc",
  "geonameId": 1269750,
  "south": 6.747139,
  "isoAlpha3": "IND",
  "north": 35.504223,
  "fipsCode": "IN",
  "population": "1173108018",
  "east": 97.403305,
  "isoNumeric": "356",
  "areaInSqKm": "3287590.0",
  "countryCode": "IN",
  "west": 68.186691,
  "countryName": "India",
  "continentName": "Asia",
  "currencyCode": "INR"
}]}

initWithNSDictionary方法

- (instancetype) initWithNSDictionary:(NSDictionary*)countryInfo_
{
    self = [super init];
    if(self) {
        NSLog(@"Country Info = %@",countryInfo_);
        self.code = [countryInfo_  valueForKey:@"countryCode"];
        self.name = [countryInfo_  valueForKey:@"countryName"];
        self.continent = [countryInfo_  valueForKey:@"continentName"];
        self.region = [countryInfo_  valueForKey:@"region"];
        self.currencyCode = [countryInfo_  valueForKey:@"currencyCode"];
        self.population = [countryInfo_  valueForKey:@"population"];
    }
    NSLog(@"code %@", code);
    return self;
}

Answer 1

由于你没有提供足够的信息，我在假设的基础上给你答复:

在你的Country类initWithNSDictionary方法应该定义这样的东西

  -(instancetype)initWithNSDictionary : (NSDictionary*)dictionary{
self = [super init];
if (self) {
    self.firstName = [dictionary objectForKey:@"firstName"];  //This is just example because you haven't add sufficient information in question
    self.lastName = [dictionary objectForKey:@"lastName"];
}
return self;
}

然后您可以创建Country的实例或对象，就像您在问题中创建的那样，

 Country *country = [[Country alloc] initWithNSDictionary:jsonObject];

确保json对象具有您在initWithNSDictionary方法中使用的键和值。我只是举了一个姓和名的例子。您应该根据您的json对象管理initWithNSDictionary中的数据。

Answer 2

你的结构是:

-Dictionary
--Array
---Dictionary

这意味着你有一个包含字典数组的顶级字典。

你的错误是，你试图用顶层字典初始化你的对象，它没有针对你提到的值的键，因此它返回nil，而你的对象反过来也有nil值。

简单地说，你传递的是一个只有以下键和值对的字典:

Key: Geonames
Value: An Array 

那么在你的init方法中，你假设它包含其他键，而实际上这些其他键只存在于数组中包含的字典中。下面的字典是:

{
  "continent": "AS",
  "capital": "Nuova Delhi",
  "languages": "en-IN,hi,bn,te,mr,ta,ur,gu,kn,ml,or,pa,as,bh,sat,ks,ne,sd,kok,doi,mni,sit,sa,fr,lus,inc",
  "geonameId": 1269750,
  "south": 6.747139,
  "isoAlpha3": "IND",
  "north": 35.504223,
  "fipsCode": "IN",
  "population": "1173108018",
  "east": 97.403305,
  "isoNumeric": "356",
  "areaInSqKm": "3287590.0",
  "countryCode": "IN",
  "west": 68.186691,
  "countryName": "India",
  "continentName": "Asia",
  "currencyCode": "INR"
}

因此，您需要从数组中获取上面提到的Dictionary，并使用它来初始化对象。

要修复它，您需要修改您的initWithDictionary方法(或者理想情况下，您调用initWithdictionary方法的方式，但现在让我们忘记它)。

- (instancetype) initWithNSDictionary:(NSDictionary*)countryInfo_
{
    self = [super init];
    if(self) {
        NSLog(@"Country Info = %@",countryInfo_);
        NSArray *internalArray = countryInfo_[@"geonames"]; //Now you got your array of dictionaries.
        if([internalArray count]>0){
            NSDictionary *internalDictionary = internalArray[0]; //Assuming there will always be only one dictionary in that array but if there are more, thats your design problem. You got your internal dictionary now
            self.code = internalDictionary[@"countryCode"];
            self.name = internalDictionary[@"countryName"];
            self.continent = internalDictionary[@"continentName"];
            self.region = internalDictionary[@"region"];
            self.currencyCode = internalDictionary[@"currencyCode"];
            self.population = internalDictionary[@"population"];
        }

    }
    NSLog(@"code %@", code);
    return self;
}

注意:这是假设在你的字典数组中总是有一个字典，或者至少只有你想要使用的第一个字典。这意味着有一些信息，你对我们隐瞒或一个真正大的设计缺陷在你的结束。

Answer 3

使用

Country *country = [[Country alloc] initWithNSDictionary:[jsonObject objectForKey:@"your key"]];
//[[NSDictionary alloc] initWithObjectsAndKeys:
                    //jsonObject ?: [NSNull null], @"jsonObject",nil]

Answer 4

将代码行改为

Country *country = [[Country alloc] initWithNSDictionary:(NSDictionary *)jsonObject];

和国家使用

中的访问变量

[countryCode setText:[country.code description]];