Pattern for determining if object is fully or partially loaded - ios

Question

The question does not strictly tied with iOS, but since I encountered this in iOS app I will speak in terms of Objective-C.
My iOS app is a client, which gets some data from server. The data from server is json, and it is mapped with my classes. The problem appears when the server send only the necessary part of the object.
Lets say the full object is
{
"a" : 1,
"b" : 2,
"c" : 3
}
My class to which it is mapped is
#class MyObject
{
int a, b, c;
}
#property (nonatomic) int a, b, c;
-(id) initFromDictionary:(NSDictionary*)dict
#end
#implementation MyObject
-(id) initFromDictionary:(NSDictionary*)dict
{
self = [super init];
if (self)
{
a = [dict[#"a"] intValue];
b = [dict[#"b"] intValue];
c = [dict[#"c"] intValue];
}
return self;
}
#end
The server can send
{
"a" : 1,
"c" : 3
}
for request getAandC and
{
"a" : 1,
"b" : 2
}
for another - getAandB (these requests are not dependent, the only thing they are similar is the object they use). I do not need any information about b in the first one and about c in the second one.
The problem is the following. When I write code for these requests I surely know which fields are returned and do not use empty field, but after some time I may forget about which request returned partial object or full, and try to use empty field. So there can be a lot of errors, which could be hard to find.
Is there any practices for that case or maybe some pattern for determining if the object is fully or partially loaded and warning the developer about it?

Answer 1

You Can Implement it as :
#implementation MyObject
-(id) initFromDictionary:(NSDictionary*)dict
{
self = [super init];
if (self)
{
a = ([dict objectForKey: #"a"]) ? [[dict objectForKey: #"a"] intValue] : 0;
b = ([dict objectForKey: #"b"]) ? [[dict objectForKey: #"b"] intValue] : 0;
c = ([dict objectForKey: #"c"]) ? [[dict objectForKey: #"c"] intValue] : 0;
// Here you can replace 0 with nil in case if variable a , b , c
are object type i.e. (id) type or You can use default value here as per your convenience so that you can easily track it if it is partially or fully Loaded
if ((a == 0) || (b == 0) || (c == 0))
{
NSLog(#"object is Partially loaded with values a : %d , b : %d , c : %d", a,b,c);
}else{
NSLog(#"object is Completely loaded with values a : %d , b : %d , c : %d", a,b,c);
}
}
return self;
}
#end
Or
#implementation MyObject
-(id) initFromDictionary:(NSDictionary*)dict
{
self = [super init];
if (self)
{
NSArray *keys = [dict AllKeys];
for(NSString * key in keys)
{
[self setValueToItsVariableForKey:key fromDictionary: dict];
}
}
return self;
}
- (void)setValueToItsVariableForKey:(NSString *)key fromDictionary: (NSDictionary *)dict
{
switch ([key intValue])
{
case : a
a = [[dict objectForKey: key] intValue];
break;
case : b
b = [[dict objectForKey: key] intValue];
break;
case : c
c = [[dict objectForKey: key] intValue];
break;
}
}
#end

Answer 2

I would approach this using the KVO pattern. What you can do is setup a counter where you increase the count by adding a KVO on the property that you want to observe. You can then set a observer on the counter and if the conter has reached the predetermined count (of all properties to be loaded) you can consider the object to be fully loaded.