iOS-初始化自定义类使用JSON返回nil

Question

我在这行代码，

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

我得到一个元素的JSONObject但为什么国家在零？

我在项目中有国家级文件，我已经通过它做了一个对象。

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

改变的代码行到

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

和访问变量从国家使用

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

此使用说明解决我的问题。

Answer 2

使用此上

Country *country = [[Country alloc] initWithNSDictionary:[jsonObject objectForKey:@"your key"]]; 

//[[NSDictionary alloc] initWithObjectsAndKeys: 
        //jsonObject ?: [NSNull null], @"jsonObject",nil] 

Answer 3

由于您没有提供足够的问题信息，我写的答案假设基础：

在您的Country类initWithNSDictionary方法应该定义类似这样的东西。

-(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，你可以为你在你的问题已经创建创建实例或Country对象，

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

确保JSON对象有你在initWithNSDictionary方法中使用的关键和价值。我刚刚举了名字和姓氏的例子。您应该根据您的json对象管理initWithNSDictionary中的数据。

Answer 4

你的结构是：

-Dictionary 
--Array 
---Dictionary 

这意味着你有一个包含字典数组的顶部字典。

你的错误是，你试图用顶级字典初始化你的对象，而顶级字典没有提供你提到的值的键，所以它返回nil，你的对象依次有nil值。

简单地说，要传递其仅具有下列键值对的字典：

Key: Geonames 
Value: An Array 

然后在您的init方法假定你是它包含了其他键的时候，其实那些其他键存在仅在数组中包含的字典中。这是下面的字典：

{ 
    "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" 
} 

所以你需要从数组中获得上述字典，并用它来初始化你的对象。

要修复它，你需要修改你的initWithDictionary方法（或者理想情况下，你调用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：这是假设将永远存在于你的字典数组一个字典或至少只是你想使用的第一个。这意味着你有一些信息隐瞒了我们，或者在你的设计上有一个很大的设计缺陷。