I've been looking for a way to serialize custom objects with NSJSONSerialization avoiding the use of third-party libraries, and I couldn't find any example. Is there any way of "automatically" create an NSDictionary and NSArray from an object, without having to create it typing in code all the object's member names yourself one by one and setting manually the values? I found a related post, but it is pretty old, things may have now changed.
Thanks
You can use KVC to ask any object for dictionaryWithValuesForKeys: which will give you a dictionary representation of the object.
If you need to change the property / key names then you want to do some mapping and (depending on what you're using the JSON for) you may find RestKit useful.
Related
JSONModel lets you convert a model object into a NSDictionary as following:
NSDictionary *dict = [myJSONModel toDictionary]
It includes all properties of the model (except optional). However, I also need to create multiple dictionaries having only some model fields required for a particular backend operation.
Some fields could be included in multiple dictionaries, so ideally, it would be awesome if I could do something like:
NSDictionary *dictOne = [myJSONModel dictionaryWithKeyMapper:myJSONMapperOne]
NSDictionary *dictTwo = [myJSONModel dictionaryWithKeyMapper:myJSONMapperTwo]
and it only returns the objects that have been mapped in that particular mapper.
I am sure there's nothing like this at present. The keymapper for every class is created only once and then is cached, so you can't changed it programatically. Plus you cannot ignore properties via the keymapper.
JSONModel is built like so that it supposes you always need to do the same transformations when you convert between JSON and your model, this way it can do the performance optimisations it does.
However "toDictionary" is not too complicated, you could try subclassing JSONModel and playing around with implementing a "toDictionaryWithFieldList" that takes in field names list and exports only those fields ... just an idea
I have an array of cached objects that I retrieve using NSCoding and NSKeyedUnarchiver. These have have many properties.
I now need to check if the contents of an object I create is identical to any of the cached objects contents in the array.
I of course cannot check if the references to the objects are equal using containsObject, but I can check if their contents are identical. I know how to achieve the end result, but what's best practice in this case? I would want it to take as little time as possible.
And keep in mind that the objects are only identical if all their properties match.
Thank you for your time!
Implement the isEqual: and hash methods on the class. The implementation of isEqual: should compare all properties.
Once you have those two methods properly implemented you can make use of collection methods such as NSArray containsObject: or NSArray indexOfObjects:, etc.
I am reading on objective-c (a nerd ranch book), and I can't help thinking about this question: How do I decide which collection type, NSArray or NSDictionary (both with or w/o their mutable subclasses), to use when reading content from URL?
Let's say am reading JSON data from a PHP script (a scenario am dealing with), which to use? I know it is stated in many references that it depends on structure of data (i.e. JSON), but could a clear outline of the two structures be outlined?
Thank you all for helping :)
NSArray is basically just an ordered collection of objects, which can be accessed by index.
NSDictionary provides access to its objects by key(typically NSStrings, but could be any object type like hash table).
To generate an object graph from a JSON string loaded via a URL, you use NSJSONSerialization, which generates an Objective-C object structure. The resulting object depends on the JSON string. If the top-level element in your JSON is an array (starts with "["), you'll get an NSArray. If the top-level element is a JSON object (starts with "{"), you'll get an NSDictionary.
You want to use NSArray when ever you have a collection of the same type of objects, and NSDictionary when you have attributes on an object.
If you have, lets say a person object containing a name, a phone number and an email you would put it in a dictionary.
Doing so allows the order of the values to be random, and gives you a more reliable code.
If you want to have more then one person you can then put the person objects in an array.
Doing so allow you to iterate the user objects.
"withContentOfURL" or "withContentOfFile" requires the data in the URL or the file to be in a specific format as it is required by Cocoa. JSON is not that format. You can only use these methods if you wrote the data to the file or the URL yourself in the first place, with the same data. If you write an NSArray, you can read an NSArray. If you write an NSDictionary, you can read an NSDictionary. Everything else will fail.
I'm trying to create an NSDictionary that keeps track of calling objects for a function. I'd like to create a unique string for each object without knowing anything about it. My first thought is to use the memory address of the object's pointer, but I'm not sure how to do that.
Any thoughts? I need to use some sort of unique id from an NSObject as the keys in my dictionary.
If your application supports iOS6 only check the NSDictionaryOfVariableBindings macro.
The code would be something like :
// Create the dictionary
NSObject *firstObject = [NSString stringWithString:#"My first item"];
NSObject *secondObject = #"[#"an", #"array", #"of", #"strings"]";
NSDictionary *theDic = NSDictionaryOfVariableBindings(firstObject, secondObject);
// Access data
NSString *singleString = [theDic objectForKey:#"firstObject"];
NSArray *listOfStrings = [theDic objectForKey:#"secondObject"];
My suggestion is not to use a dictionary. If you were to place them into an array, you could think of it as a dictionary with automatically generated unique keys (the indexes). It's really exactly what you are describing. If for some reason you have to use a dictionary, my suggestion is to implement that same model I'm speaking of, but you would have to generate and maintain the keys.
While I agree that your solution sounds like it may not be the best approach, have you considered -hash in the NSObject protocol? All NSObjects should return one. Be forewarned that it's a hash, so there's a chance that two different objects could have the same hash.
You could also consider a category on NSObject that your collection implements. The category could generate a UUID to use as a key.
Right now I am using ArrayCollection. But I want to change that to Set as I want make sure do duplicate values come.
var addressList:ArrayCollection = new ArrayCollection();
One way is I can use Dictionary and store addresses as a key. And I can just use keys to iterate.
But I am looking for Java HashSet like implementation.
You want to download Polygonal Data Structures. The swc contains a HashSet. If you want Java-style template syntax for Flash, you should also check out Haxe.
The AS3 equivalent to HashMap or HashSet is the Dictionary class, and to a lesser extent, the Object class. Object keys are stored as strings, while with Dictionary the keys are objects. You can't have duplicate entries with either. Are you looking for a specific implementation other than that?