I have a json structure like this
I am trying to check for the "type" in each nested widgets array.So if it is of a certain type then i am trying to extract properties like fade steps,width, height etc.
Is there a way of doing it using the for loop?
Right now I am doing like this:
for (NSString *widgetArray in widgets)
{
NSLog(#"%#", widgetArray);
}
Its printing the contents, How do I extract corresponding values?
for(NSDictionary *asset in [assets allValues])
{
NSString *type = asset[#"type"];
if ([type isEqualToString:#"gradient"])
{
[gradients addObject:asset];
}
This is the pseudo code provided by one of the members which helped me access the contents of the dictionary, I am not able to apply a similar logic to the nested array structure.
Since the problem is recursive search, you have to use stack. Here are the steps:
Create NSMutableArray that will serve as the stack. Now it is empty.
Take the root widgets array and put all its objects onto the stack (-addObjectsFromArray:).
Take out the first widget (NSDictionary) in stack. Be sure to take it out of the stack (-removeObjectAtIndex:) after storing it in variable.
Do your type comparision and other stuff with that variable.
Take its subwidgets and put all of them onto the stack just like in step 2.
If the stack has something in it, repeat from step 3. Otherwise you processed all widgets.
Pseudo code:
// 1
NSMutableArray *stack = [NSMutableArray array];
// 2
[stack addObjectsFromArray:rootWidgets];
while (stack.count > 0) {
// 3
NSDictionary *widgetDict = [stack objectAtIndex:0];
[stack removeObjectAtIndex:0];
// 4
if ([[widgetDict objectForKey:#"type"] isEqualToString:...]) // Do whatever...
// 5
[stack addObjectsFromArray:[widgetDict objectForKey:#"widgets"]];
}
// 6
// You are done...
To check the type of each element, use the NSObject isKindOfClass: method.
So, you might have something like:
if ([obj isKindOfClass:[NSDictionary class]]) { ... }
Or
if ([obj isKindOfClass:[NSArray class]]) { ... }
Like #H2CO3 says, you use objectAtIndex: to access array elements and objectForKey: to access dictionary elements.
EDIT: I just realized that by "of a certain type" the OP meant the value of the "type" field, rather than the objective-c class of an entry. Still, it is often useful when reading JSON data to determine whether an entry is an array or dictionary, so I will leave my answer here.
In the latest objective C you can use subscripting like C arrays. For example,
NSLog(#"%#", widgetArray[i]);
For dictionaries you can extract via key:
NSString* id = myDict[#"id"];
Related
I need to be able to read some JSON that I no control over. Basically the JSON looks like this:
[ [{"a":1,"b":2}], [{"a":1,"b":2}], [{"a":1,"b":2}] ]
I'm trying to parse it with RestKit and I just couldn't figure out how to handle the first two levels of the object hierarchy. The items in question are more complicated but they are not the issue here. The issue is how should I skip the second array that empirically would seem to have only one item every time.
In short, I'd like to flatten this and get single array instead of an array of arrays.
I've tried to create a mapping for NSArraybut from there I have no idea how to map the items in this array. The inner array has no name and I couldn't figure out how to reference it in the mappings.
Any working solution is greatly appreciated.
Update
The issue here is how should I create the JSON mappings and not how to read multi-dimensional arrays. I've tried the following but I don't know if the mapping for NSArray is ok. The following mapping gives an example, but it doesn't work:
secondMapping = [RKObjectMapping mappingForClass:[MyClass class]];
[secondMapping addAttributeMappingsFromDictionary:#{
#"a": #"a",
#"b": #"b"
}];
firstMapping = [RKObjectMapping mappingForClass:[NSArray class]];
[firstMapping addPropertyMapping:[RKRelationshipMapping relationshipMappingFromKeyPath:nil
toKeyPath:nil
withMapping:secondMapping]];
Can't you just copy over the single element of the inner arrays to another array?
NSMutableArray *newArr = [NSMutableArray new];
for (NSArray *innerArr in jsonObject)
[newArr addObject:innerArr[0]];
You don't say what you're trying to map to, it will be a little difficult to map the base dictionary into a custom object. If you create an object with an array property:
#property (strong, nonatomic) NSArray *items;
Then you can map an array of these objects where the items array will contain NSDictionary instances. This would use a nil keypath to map to the items key.
The best way to make this work without giving up on RestKit was to add a custom JSON serializer. I only needed the secondMapping and mappings from there on required to match the object hierarchy.
[RKMIMETypeSerialization registerClass:[MySerialization class] forMIMEType:#"application/json"];
And here is my serializer:
#implementation MySerialization
+ (id)objectFromData:(NSData *)data error:(NSError **)error
{
id object = [NSJSONSerialization JSONObjectWithData:data options:0 error:error];
// Fix the following weirdness in JSON response:
// [ [{route_1}], ..., [{route_n}] ]
if ([object isKindOfClass:[NSArray class]]
&& [[object lastObject] isKindOfClass:[NSArray class]])
{
object = [object valueForKeyPath:#"#unionOfArrays.#self"];
}
return object;
}
+ (NSData *)dataFromObject:(id)object error:(NSError **)error
{
return [NSJSONSerialization dataWithJSONObject:object options:0 error:error];
}
#end
Other alternative is block in RKResponseMapperOperation mentioned here
- (void)setWillMapDeserializedResponseBlock:(id ( ^ ) ( id deserializedResponseBody ))block
I chose the custom serializer as it was simpler, but this is definitely more scalable way.
From my experience with RestKit, this will only work for ONE mapping. Use #"" as the root keypath and you should be able to get it to work. However what you probably need to do if you intend to use RestKit for your entire application is to modify the response data to include the root element name.
I don't know if what I see with a popup button populated by bindings with a value transformer is the way it's supposed to be or not -- the unusual thing I'm seeing (at least with respect to what I've seen with value transformers and table views) is that the "value" parameter in the transformedValue: method is the whole array bound to the array controller, not the individual strings in the array. When I've done this with table views, the transformer is called once for each displayed row in the table, and the "value" parameter is whatever object is bound to that row and column, not the whole array that serves as the content array for the array controller.
I have a very simple app to test this. In the app delegate there is this:
+(void)initialize {
RDTransformer *transformer = [[RDTransformer alloc] init];
[NSValueTransformer setValueTransformer:transformer forName:#"testTransformer"];
}
- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
self.theData = #[#{#"name":#"William", #"age":#"24"},#{#"name":#"Thomas", #"age":#"23"},#{#"name":#"Alexander", #"age":#"64"},#{#"name":#"James", #"age":#"47"}];
}
In the RDTransformer class is this:
+ (Class)transformedValueClass {
return [NSString class];
}
+(BOOL)allowsReverseTransformation {
return NO;
}
-(id)transformedValue:(id)value {
NSLog(#"%#",value);
return value;
}
In IB, I added an NSPopupButton to the window and an array controller to the objects list. The content array of the controller is bound to App Delegate.theData, and the Content Values of the popup button is bound to Array Controller.arrangedObjects.name with the value transformer, testTransformer.
When I run the program, the log from the transformedValue: method is this:
2012-09-19 20:31:39.975 PopupBindingWithTransformer[793:303] (
)
2012-09-19 20:31:40.019 PopupBindingWithTransformer[793:303] (
William,
Thomas,
Alexander,
James
)
This doesn't seem to be other people's experience from what I can see on SO. Is there something I'm doing wrong with either the bindings or the value transformer?
Unfortunately, this is how NSPopUpButton works. The problem is not limited to that control. If you try binding an NSArrayController.contentArray to another NSArrayControllers.arrangedObject.someProperty you will get the same problem. Here is a simple workaround that I use in all my value transformers, which makes them work with both tables and popups:
You can modify your value transformer in the following way:
-(id)transformedArrayValue:(NSArray*)array
{
NSMutableArray *result = [NSMutableArray array];
for (id value in array)
[result addObject:[self transformedValue:value]];
return result;
}
-(id)transformedValue:(id)value
{
if ([value isKindOfClass:[NSArray class]])
return [self transformedArrayValue:value];
// Do your normal-case transform...
return [value lowercaseString];
}
It's not perfect but it's easy to replicate. I actually put the transformedArrayValue: in a class category so that I don't need to copy it everywhere.
This is probably a long shot, but I've got objects with a lot of properties. The values of these objects are populated from NSDictionary's created from a database request. Because of this, there may be NSNull values contained in those NSDictionaries that will automatically get assigned to the properties. I need the properties to automatically discard values/objects that aren't of the correct type. Currently I do it like this:
- (void) setViewID:(NSString *)viewID{
if (!viewID || [viewID isKindOfClass:[NSString class]]) _viewID = viewID;
}
But that ends up being a lot of extra code when I've got 30-50 properties. Is there a way to synthesize this behavior? It seems like it would be a common enough requirement, but I can't seem to find a way to do it aside from writing it all out.
Why not check for NSNull when you are going through the dictionary? E.g.
for (NSString *key in dictionary) {
id value = [dictionary objectForKey:key];
if (value == [NSNull null]) {
value = nil;
}
[self setValue:value forKey:key];
}
I want to add object to array only if the array already does not contain that object.
How to do opposite of containsObject method in NSArray ?
Use an NSMutableOrderedSet, whose addObject: method does exactly what you want:
Appends a given object to the mutable ordered set, if it is not already a member.
Here's how I'd do it:
if (![myArray containsObject:objectToAdd]){
[myArray addObject:objectToAdd];
}
More detail here:
https://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/NSArray_Class/NSArray.html
Note that because the containsObject method queries every object in the array there are some performance considerations when using it on larger arrays.
if your object is of NSString* type you can do fast enumeration like this
BOOL found = NO;
for(NSString *object in YourArray)
{
if([object isEqualtoString:#"My text"])
{
found = YES;
}
}
if(!found)
{
//addObject
}
there are many isEqual methods in objective-c for different data types
If you can't get an object with objectAtIndex: from an NSSet then how do you retrieve objects?
There are several use cases for a set. You could enumerate through (e.g. with enumerateObjectsUsingBlock or NSFastEnumeration), call containsObject to test for membership, use anyObject to get a member (not random), or convert it to an array (in no particular order) with allObjects.
A set is appropriate when you don't want duplicates, don't care about order, and want fast membership testing.
NSSet doesn't have a method objectAtIndex:
Try calling allObjects which returns an NSArray of all the objects.
it is possible to use filteredSetUsingPredicate if you have some kind of unique identifier to select the object you need.
First create the predicate (assuming your unique id in the object is called "identifier" and it is an NSString):
NSPredicate *myPredicate = [NSPredicate predicateWithFormat:#"identifier == %#", identifier];
And then choose the object using the predicate:
NSObject *myChosenObject = [mySet filteredSetUsingPredicate:myPredicate].anyObject;
NSArray *myArray = [myNSSet allObjects];
MyObject *object = [myArray objectAtIndex:(NSUInteger *)]
replace NSUInteger with the index of your desired object.
For Swift3 & iOS10 :
//your current set
let mySet : NSSet
//targetted index
let index : Int
//get object in set at index
let object = mySet.allObjects[index]
NSSet uses the method isEqual: (which the objects you put into that set must override, in addition, the hash method) to determine if an object is inside of it.
So, for example if you have a data model that defines its uniqueness by an id value (say the property is:
#property NSUInteger objectID;
then you'd implement isEqual: as
- (BOOL)isEqual:(id)object
{
return (self.objectID == [object objectID]);
}
and you could implement hash:
- (NSUInteger)hash
{
return self.objectID; // to be honest, I just do what Apple tells me to here
// because I've forgotten how Sets are implemented under the hood
}
Then, you can get an object with that ID (as well as check for whether it's in the NSSet) with:
MyObject *testObject = [[MyObject alloc] init];
testObject.objectID = 5; // for example.
// I presume your object has more properties which you don't need to set here
// because it's objectID that defines uniqueness (see isEqual: above)
MyObject *existingObject = [mySet member: testObject];
// now you've either got it or existingObject is nil
But yeah, the only way to get something out of a NSSet is by considering that which defines its uniqueness in the first place.
I haven't tested what's faster, but I avoid using enumeration because that might be linear whereas using the member: method would be much faster. That's one of the reasons to prefer the use of NSSet instead of NSArray.
for (id currentElement in mySet)
{
// ** some actions with currentElement
}
Most of the time you don't care about getting one particular object from a set. You care about testing to see if a set contains an object. That's what sets are good for. When you want to see if an object is in a collection sets are much faster than arrays.
If you don't care about which object you get, use -anyObject which just gives you one object from the set, like putting your hand in a bag and grabbing something.
Dog *aDog = [dogs anyObject]; // dogs is an NSSet of Dog objects
If you care about what object you get, use -member which gives you back the object, or nil if it's not in the set. You need to already have the object before you call it.
Dog *spot = [Dog dogWithName:#"Spot"];
// ...
Dog *aDog = [dogs member:spot]; // Returns the same object as above
Here's some code you can run in Xcode to understand more
NSString *one = #"One";
NSString *two = #"Two";
NSString *three = #"Three";
NSSet *set = [NSSet setWithObjects:one, two, three, nil];
// Can't use Objective-C literals to create a set.
// Incompatible pointer types initializing 'NSSet *' with an expression of type 'NSArray *'
// NSSet *set = #[one, two, three];
NSLog(#"Set: %#", set);
// Prints looking just like an array but is actually not in any order
//Set: {(
// One,
// Two,
// Three
// )}
// Get a random object
NSString *random = [set anyObject];
NSLog(#"Random: %#", random); // Random: One
// Iterate through objects. Again, although it prints in order, the order is a lie
for (NSString *aString in set) {
NSLog(#"A String: %#", aString);
}
// Get an array from the set
NSArray *array = [set allObjects];
NSLog(#"Array: %#", array);
// Check for an object
if ([set containsObject:two]) {
NSLog(#"Set contains two");
}
// Check whether a set contains an object and return that object if it does (nil if not)
NSString *aTwo = [set member:two];
if (aTwo) {
NSLog(#"Set contains: %#", aTwo);
}