I'm getting an NSCFDictionary returned to me and I can't figure out how to use it. I know it's of type NSCFDictionary because I printed the class and it came out as __NCSFDictionary. I can't figure out how to do anything with it.
I'm just trying to hold onto it for now but can't even get that to work:
NSDictionary *dict = [[NSURLCredentialStorage sharedCredentialStorage] allCredentials];
for(NSURLProtectionSpace key in [dict keyEnumerator])
{
NSCFDictionary *value = [dict objectForKey:key];
}
The class reference for allCredentials says its supposed to return a dictionary whose values are also dictionaries. My assignment statement isn't working though. Do I need a cast of some kind?
NSDictionary and the other collection classes are actually class clusters: several concrete subclasses classes masquerading under the interface of a single class: they all provide the same functionality (because they are subclasses of the same class — in NSDictionary's case, this involves the three "primitive methods" -count, -objectForKey:, and -keyEnumerator), but have different internal workings to be efficient in different situations, based on how they're created and what type of data they may be storing.
NSCFDictionary is simply a concrete subclass of NSDictionary. That is, your NSDictionaries may actually be NSCFDictionary instances, but you should treat them as instances of NSDictionary, because that will provide you with the required dictionary-storage functionality.
NSDictionary *value = [dict objectForKey:key];
Now, another reason your code doesn't work: NSURLProtectionSpace is a class, so you should use it as a pointer, like this:
for (NSURLProtectionSpace *key ...
NSCFDictionary is the private subclass of NSDictionary that implements the actual functionality. It's just an NSDictionary. Just about any NSDictionary you use will be an NSCFDictionary under the hood. It doesn't matter to you code. You can type the variable as NSDictionary and use it accordingly.
I have an NSCFDictionary that is actually a NSMutableDictionary object, I can delete items from it. I mention this to further clarify jtbandes' answer: the NSCFDictionary object may be any object that inherits from NSDictionary.
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I'm getting an NSCFDictionary returned to me and I can't figure out how to use it. I know it's of type NSCFDictionary because I printed the class and it came out as __NCSFDictionary. I can't figure out how to do anything with it.
I'm just trying to hold onto it for now but can't even get that to work:
NSDictionary *dict = [[NSURLCredentialStorage sharedCredentialStorage] allCredentials];
for(NSURLProtectionSpace key in [dict keyEnumerator])
{
NSCFDictionary *value = [dict objectForKey:key];
}
The class reference for allCredentials says its supposed to return a dictionary whose values are also dictionaries. My assignment statement isn't working though. Do I need a cast of some kind?
NSDictionary and the other collection classes are actually class clusters: several concrete subclasses classes masquerading under the interface of a single class: they all provide the same functionality (because they are subclasses of the same class — in NSDictionary's case, this involves the three "primitive methods" -count, -objectForKey:, and -keyEnumerator), but have different internal workings to be efficient in different situations, based on how they're created and what type of data they may be storing.
NSCFDictionary is simply a concrete subclass of NSDictionary. That is, your NSDictionaries may actually be NSCFDictionary instances, but you should treat them as instances of NSDictionary, because that will provide you with the required dictionary-storage functionality.
NSDictionary *value = [dict objectForKey:key];
Now, another reason your code doesn't work: NSURLProtectionSpace is a class, so you should use it as a pointer, like this:
for (NSURLProtectionSpace *key ...
NSCFDictionary is the private subclass of NSDictionary that implements the actual functionality. It's just an NSDictionary. Just about any NSDictionary you use will be an NSCFDictionary under the hood. It doesn't matter to you code. You can type the variable as NSDictionary and use it accordingly.
I have an NSCFDictionary that is actually a NSMutableDictionary object, I can delete items from it. I mention this to further clarify jtbandes' answer: the NSCFDictionary object may be any object that inherits from NSDictionary.
in my app I have no problem withs saving/retrieving string values(like myTextField.text) into NSUserDefaults but whatever i do to store NSDictionary i coldn't succeed. And i tried a lot of answer from this site+ Google. Can anyone please help? Here is my code too:
id result=[NSJSONSerialization JSONObjectWithData:data options:
NSJSONReadingMutableContainers error:&error];
NSLog(#"Result: %#", result);
NSDictionary *dict= [result objectForKey:#"message"];
//i want to store dict sub dictionary
*EDIT*Note:The dictionary contains a kind of array of objects, and the objects are all members of property list(NSString, NSDate, ...)
What the other answers are trying to tell you is, you have to get rid of your (id). NSUserDefaults and the compiler will complain and throw warnings if you try and put an id into the user defaults. Try it out this way.
NSDictionary *result = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableContainers error:&error];
if (result) {
[[NSUserDefaults standardUserDefaults] setObject:result forKey:#"yourUniqueKey"];
}
This is because some of the objects in your NSDictionary are not Objective C primitive objects, or to put it a better way, iOS doesn't know how to convert the custom data in the NSDictionary to a form that can be saved and loaded again.
So you need to learn how to get those custom objects to conform to NSCoding.
Here is a related question that should have some useful information for you.
It depends on what you are storing. Apple's documentation says
The NSUserDefaults class provides convenience methods for accessing common types such as floats, doubles, integers, Booleans, and URLs. A default object must be a property list, that is, an instance of (or for collections a combination of instances of): NSData, NSString, NSNumber, NSDate, NSArray, or NSDictionary. If you want to store any other type of object, you should typically archive it to create an instance of NSData. For more details, see Preferences and Settings Programming Guide.
I assume you are trying to store a type other than the listed ones.
Im having the following problem:
I've made a NSMutableArray "array" that is going to contain objects of a class named "Class". At the start that array should be empty and it must be filled during the program's execution.
As I never actually told the compiler that my NSMutableArray will be holding elements of the class Class, when I try to write the appropriate methods the compiler wont let me do it.
This is my first experience on Objective-C and iPhone development. I used to code in C/C++ where I declared my arrays in the following way:
Class array[NUMBEROFELEMENTS];
Is there any way to do this in Objective-C?
Thanks!
The truth is that is doesn't matter to the NSMutableArray what type of object it is. NSMutableArray simply stores pointers to all the objects they contain, or reference.
The trick is when you pull the object back out of the array you need to create a new pointer based on the appropriate type:
MyObject *myObject = [myArray objectAtIndex:0];
Then you can use the object however you like:
[myObject doThatThingWithThisValue:10];
Or whatever you need.
Arrays in Objective-C Cocoa are objects (as well as other collections, sets, dictionaries). Arrays can contain references to objects of any type, so the type for the array is simply NSArray, NSMutableArray, etc...
Since they are objects, you can send them messages to manipulate their content.
I suggest you take a look at Apple's excellent Collections Programming Topics, which explain the rudiments of collections.
Here is a quick example :
// two objects of different types
NSNumber *n = [NSNumber numberWithInteger:10];
NSString *s = #"foo";
// alloc/init a new mutable array
NSMutableArray *a = [NSMutableArray arrayWithCapacity:10];
// add an object
[a addObject:n];
[a addObject:s];
// array a now contains a NSNumber and a NSString
Well, you can still have C-style arrays in Objective-C.
However, the characteristics of Objective-C (some people will call it strength, other will call it weakness) is that it has dynamic typing of objects and dynamic dispatch.
It has NSArray and NSMutableArray which are not specialized for the certain class. It can store objects of non-compatible classes.
You can use the following idiom: [obj isMemberOfClass: [Class type]] to make sure an array element is of the desired type and then cast to Class*.
You can also use for-each loop (aka Fast Enumeration):
NSMutableArray* array = //... initialize your array
for (Class* elm in array) {
elm.your_property = 10;
}
The NSMutableArray can store every NSObject, but can I mention the NSMutableArray can get store my item only, for example, a NSMutableArray that store NSString only?
I remember that the java array can do that, can the objective C array do the similar things? Thanks.
Objective-C does not have this kind of generic constraint on NSArray/NSMutableArray. You have therefore two solutions:
Subclass NSArray/NSMutableArray and check for element type. It is strongly discouraged as NSArray/NSMutableArray is a class "cluster" and not obvious to subclass.
Create a category with specific methods that check the right type. You will have a compile-time enforcement of the type.
You can try it like this -
NSMutableArray *arr = [[[NSMutableArray alloc] init] autorelease];
if([obj isKindOfClass:[NSString class]])
[arr addObject:obj];
This way you end up adding only NSString to your arr.
Not by default, no. NSArray and its mutable counterpart just store pointers which happen to point obj-c objects. These objects can of any type. It would be up to you to make sure that only NSString's get in your array.
You could potentially subclass NSArray and override the addObject: methods such that they throw an exception if you try to add a non-NSString object.
I'm a bit confused with key value coding and to-many relationships. I've read that when having such relationship I should use [object mutableArrayValueForKey:#"key"]; to retrieve
the mutable array that holds the objects in that ordered relationship.
What I don't understand is what's the difference between mutableArrayValueForKey or just
valueForKey.
Let me illustrate with an example (array is an NSMutableArray of self setup as a property):
id array1= [self valueForKey:#"array"];
NSLog(#"first element %#",[array1 objectAtIndex:1]);
id array2 = [self mutableArrayValueForKey:#"array"];
NSLog(#"first element %#",[array2 objectAtIndex:1]);
Both calls return exactly the same. In that case, what is the benefit or different of the second one?
Cheers!
mutableArrayValueForKey does not return "array", it returns a proxy for "array." You can see this if you print out the classes:
NSLog(#"%#", [self.array class]);
NSLog(#"%#", [[self valueForKey:#"array"] class]);
NSLog(#"%#", [[self mutableArrayValueForKey:#"array"] class]);
This prints:
2010-02-24 20:06:44.258 Untitled[25523:a0f] NSCFArray
2010-02-24 20:06:44.275 Untitled[25523:a0f] NSCFArray
2010-02-24 20:06:44.276 Untitled[25523:a0f] NSKeyValueSlowMutableArray
Read over the documentation for mutableArrayValueForKey for details on how that proxy works. In this particular case, you happen to have a real NSMutableArray as an ivar. But what if there were no such ivar? You can implement KVC without an ivar backing the property, with methods like countOf<Key> and objectIn<Key>AtIndex:. There's no rule that there be an actual "array" ivar, as long as you can return sensible results to the KVC methods.
But what if you want to expose an NSMutableArray interface, but you don't have a real NSMutableArray? That's what mutableArrayValueForKey is for. It returns a proxy that when accessed will translate into KVC methods back to you, including sending you mutating to-many methods like insertObject:in<Key>AtIndex:.
This even happens in the case that you have a real ivar (as in your case), you just don't notice it because the proxy behaves so much like the real object.
The first element is actually objectAtIndex:0, not objectAtIndex:1.
Also, the second method ensures that you can modify the returned array with addObject: and removeObjectAtIndex:, even if the value for the key #"array" is an immutable array.