Is there a way to store a selector in an NSDictionary, without storing it as an NSString?
SEL is just a pointer, which you could store in an NSValue:
NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:
[NSValue valueWithPointer:#selector(foo)], #"foo",
nil];
To get the selector back, you can use:
SEL aSel = [[dict objectForKey:#"foo"] pointerValue];
An alternative to Georg's solution would be to convert the selector into an NSString before storing it the NSDictionary:
NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:
NSStringFromSelector(#selector(foo)), #"foo",
nil];
SEL selector = NSSelectorFromString([dict objectForKey:#"foo"]);
This technique, though uses more memory, gives you the ability to serialize the entire NSDictionary as a string via libraries like JSONKit.
An NSDictionary is really just a CFDictionary that retains and releases all keys and values. If you create a CFDictionary directly, you can set it up to not retain and release values. You can typecast a CFDictionaryRef to an NSDictionary * and vice versa.
In case of using UILocalNotification the only way is to use NSSelectorFromString([dict objectForKey:#"foo"]). With valueWithPointer the app crashing when setting userInfo property of UILocalNotification object. Be careful.
While Georg's answer should work, NSValue does also support encoding any value using an Objective-C type encoding string, which has a special way of representing SEL— with a ":" (as opposed to the "^v" produced by -valueWithPointer:, which translates into void *).
source: Objective-C Runtime Programming Guide - Type Encodings
Working off of Georg's solution, the best API-compliant way to put a SEL into an NSValue into an NSDictionary would be:
// store
NSDictionary *dict = #{
#"foo": [NSValue value:&#selector(foo) withObjCType:#encode(SEL)]
};
// retrieve
SEL aSel;
[dict[#"foo"] getValue:&aSel];
The rationale for handling a SEL as its own beast is that the docs describe it as “an opaque type”— which means that its internal workings (even what it's typedefd to) are off-limits to app programmers; Apple may mix it up at any time in the future.
Also, using void *s to force the system to do what you want it to do was useful in C back in the '90s, when most of us didn't know any better. You're better than that now.
The above approach should only be used if the retrieval of the SEL happens during the program's running duration— you shouldn't be storing that NSDictionary to disk. If you do need to store SELs long-term (across app launches), you should follow David H's approach and convert it to an NSString.
Related
I added Book object in bookController (NSCreeController). Now i want to get stored Book object when i select the row.
- (IBAction)addClicked:(id)sender {
NSTimeInterval timeStamp = [[NSDate date] timeIntervalSince1970];
// NSTimeInterval is defined as double
NSUInteger indexArr[] = {0,0};
Book *obj = [[Book alloc] init];
NSString *dateString = [NSDateFormatter localizedStringFromDate:[NSDate date] dateStyle:NSDateFormatterNoStyle timeStyle:NSDateFormatterLongStyle];
obj.title = [NSString stringWithFormat:#"New %#",dateString];
obj.filename = [NSString stringWithFormat:#"%d",arc4random()%100000];
[self.booksController insertObject:obj atArrangedObjectIndexPath:[NSIndexPath indexPathWithIndexes:indexArr length:2]];
}
I concede there perhaps could be a better solution--
I am unfamiliar with how NSTreeController works, but I looked a the class reference and noticed that it has a content property, similar to an NSArrayController (Which I am familiar with grabbing specific objects from).
I believe that if the content property is actually of type of some kind of tree data structure, my answer here probably won't work. The class reference says this about content:
The value of this property can be an array of objects, or a
single root object. The default value is nil. This property is
observable using key-value observing.
So this is what I historically have done with the expected results:
NSString *predicateString = [NSString stringWithFormat:NEVER_TRANSLATE(#"(filename == %#) AND (title == %#)"), #"FILENAME_ARGUMENT_HERE", #"TITLE_ARGUMENT_HERE"];
NSArray *matchingObjects = [[self content] filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:predicateString]];
Then simply calling -objectAtIndex: will grab you your object. Note that the NSArray will be empty if the object doesn't exist, and if you have duplicate objects, there will be multiple objects in the array.
I also searched for an answer to your question, and found this SO thread:
Given model object, how to find index path in NSTreeController?
It looks pretty promising if my solution doesn't work, the author just steps through the tree and does an isEqual comparison.
If you could (if it's not too much trouble), leave a comment here to let me know what works for you, I'm actually curious :)
i've made a plist as a dictionary with dictionary entries, one for each ABRecord property that i want to use later.
these dictionaries are key/value NSStrings like this:
kABEmailProperty/email.
i want to be able to use the unpacked plist to gather values from a specified ABRecord by enumerating the unpacked plist dictionary (assume inRecord is an ABRecord):
__block NSMutableArray *valueGroup = [[NSMutableArray alloc] init];
[self.propsDict enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
NSString *valueString = [inRecord valueForProperty:key];
if (valueString) {
NSDictionary *dict = [NSDictionary dictionaryWithObject:valueString forKey:obj];
[valueGroup addObject:dict];
}
}
}];
how do i properly refer to key, so that it is the ABRecord global property reference in ABGlobals.h instead of the string that is stored in the plist ?
i've tried using &key, and (id)key, and (void *)key, but i'm really just flailing around.
i am unsuccessful in searching through the various questions regarding using global externs, although that has been informative.
If I understand you correctly, you've got the following:
NSString *foo = "kABEmailProperty";
And you want to be able to do something like this:
[inRecord valueForProperty:kABEmailProperty];
Based on the value of foo. Correct? There's no way to do this directly, because the name "kABEmailProperty" isn't (easily) accessible at runtime; it's just a compile-time name.
My suggestion would be to make a dictionary with all keys in it; something like this:
NSDictionary *keys = [NSDictionary dictionaryWithObjectsAndKeys:kABEmailProperty, #"kABEmailProperty", kABOtherProperty, #"kABOtherProperty", ..., nil];
And then you can do something like this:
[inRecord valueForProperty:[keys objectForKey:foo]];
i.e. Make a mapping from the string #"kABEmailProperty" to the value that kABEmailProperty actually has.
I often use Transformable for Core Data attributes, so I can change them later.
However, it seems like, if I want to use NSPredicate to find a NSManagedObject, using "uniqueKey == %#", or "uniqueKey MATCHES[cd] %#", it's not working as it should.
It always misses matching objects, until I change the attributes of the uniqueKey of the matching object to have specific class like NSString, or NSNumber.
Can someone explain the limitation of using NSPredicate with Transformable attributes?
Note: I'm not sure when/if this has changed since 5/2011 (from Scott Ahten's accepted answer), but you can absolutely search with NSPredicate on transformable attributes. Scott correctly explained why your assumptions were broken, but if Can someone explain the limitation of using NSPredicate with Transformable attributes? was your question, he implied that it is not possible, and that is incorrect.
Since the is the first google hit for "Core Data transformable value search nspredicate" (what I searched for trying to find inspiration), I wanted to add my working answer.
How to use NSPredicate with transformable properties
Short, heady answer: you need to be smart about your data transformers. You need to transfrom the value to NSData that contains what I'll call "primitive identifying information", i.e. the smallest, most identifying set of bytes that can be used to reconstruct your object. Long answer, ...
Foremost, consider:
Did you actual mean to use a transformable attribute? If any supported data type -- even binary data -- will suffice, use it.
Do you understand what transformable attributes actually are? How they pack and unpack data to and from the store? Review Non-Standard Persistent Attributes in Apple's documentation.
After reading the above, ask: does custom code that hides a supported type "backing attribute" work for you? Possibly use that technique.
Now, past those considerations, transformable attributes are rather slick. Frankly, writing an NSValueTransformer "FooToData" for Foo instances to NSData seemed cleaner than writing a lot of adhoc custom code. I haven't found a case where Core Data doesn't know it needs to transform the data using the registered NSValueTransformer.
To proceed simply address these concerns:
Did you tell Core Data what transformer to use? Open the Core Data model in table view, click the entity, click the attribute, load the Data Model Inspector pane. Under "Attribute Type: Transformable", set "Name" to your transformer.
Use a default transformer (again, see the previous Apple docs) or write your own transformer -- transformedValue: must return NSData.
NSKeyedUnarchiveFromDataTransformerName is the default transformer and may not suffice, or may draw in somewhat-transient instance data that can make two similar objects be different when they are equal.
The transformed value should contain only -- what I'll call -- "primitive identifying information". The store is going to be comparing bytes, so every byte counts.
You may also register your transformer globally. I have to do this since I actually reuse them elsewhere in the app -- e.g. NSString *name = #"FooTrans"; [NSValueTransformer setValueTransformer:[NSClassFromString(name) new] forName:name];
You probably don't want to use transforms heavily queried data operations - e.g. a large import where the primary key information uses transformers - yikes!
And then in the end, I simply use this to test for equality for high-level object attributes on models with NSPredicates -- e.g. "%K == %#" -- and it works fine. I haven't tried some of the various matching terms, but I wouldn't be surprised if they worked sometimes, and others not.
Here's an example of an NSURL to NSData transformer. Why not just store the string? Yeah, that's fine -- that's a good example of custom code masking the stored attribute. This example illustrates that an extra byte is added to the stringified URL to record if it was a file URL or not -- allowing us to know what constructors to use when the object is unpacked.
// URLToDataTransformer.h - interface
extern NSString *const kURLToDataTransformerName;
#interface URLToDataTransformer : NSValueTransformer
#end
...
// URLToDataTransformer.m - implementation
#import "URLToDataTransformer.h"
NSString *const kURLToDataTransformerName = #"URLToDataTransformer";
#implementation URLToDataTransformer
+ (Class)transformedValueClass { return [NSData class]; }
+ (BOOL)allowsReverseTransformation { return YES; }
- (id)transformedValue:(id)value
{
if (![value isKindOfClass:[NSURL class]])
{
// Log error ...
return nil;
}
NSMutableData *data;
char fileType = 0;
if ([value isFileURL])
{
fileType = 1;
data = [NSMutableData dataWithBytes:&fileType length:1];
[data appendData:[[(NSURL *)value path] dataUsingEncoding:NSUTF8StringEncoding]];
}
else
{
fileType = -1;
data = [NSMutableData dataWithBytes:&fileType length:1];
[data appendData:[[(NSURL *)value absoluteString] dataUsingEncoding:NSUTF8StringEncoding]];
}
return data;
}
- (id)reverseTransformedValue:(id)value
{
if (![value isKindOfClass:[NSData class]])
{
// Log error ...
return nil;
}
NSURL *url = nil;
NSData *data = (NSData *)value;
char fileType = 0;
NSRange range = NSMakeRange(1, [data length]-1);
[data getBytes:&fileType length:1];
if (1 == fileType)
{
NSData *actualData = [data subdataWithRange:range];
NSString *str = [[NSString alloc] initWithData:actualData encoding:NSUTF8StringEncoding];
url = [NSURL fileURLWithPath:str];
}
else if (-1 == fileType)
{
NSData *actualData = [data subdataWithRange:range];
NSString *str = [[NSString alloc] initWithData:actualData encoding:NSUTF8StringEncoding];
url = [NSURL URLWithString:str];
}
else
{
// Log error ...
return nil;
}
return url;
}
#end
Transformable attributes are usually persisted as archived binary data. As such, you are attempting to compare an instance of NSData with an instance of NSString or NSNumber.
Since these classes interpret the same data in different ways, they are not considered a match.
you can try this way
NSExpression *exprPath = [NSExpression expressionForKeyPath:#"transformable_field"];
NSExpression *exprKeyword = [NSExpression expressionForConstantValue:nsdataValue];
NSPredicate *predicate = [NSComparisonPredicate predicateWithLeftExpression:exprPath rightExpression:exprKeyword modifier:NSDirectPredicateModifier type:NSEqualToPredicateOperatorType options:0];
I have an NSMutableArray i am trying to convert into a string.
Declaring my NSMutableArray...
NSMutableArray *listData;
And later inside a method...
NSString *foo = [listData componentsJoinedByString:#"|"];
NSLog(#"%#",foo);
It seems no matter what i try i keep getting EXC_BAD_ACCESS.
To make sure each element in my array was an NSString i also tried this...
NSMutableArray *mArray = [[NSMutableArray alloc] init];
for (id ln in listData) {
NSString *boo = [NSString stringWithFormat: #"%#",ln];
[mArray addObject:boo];
}
NSString *foo = [mArray componentsJoinedByString:#"|"];
NSLog(#"%#",foo);
I can manipulate my NSMutableArray by adding/deleting objects in the same method or other methods inside my class. But when i try "componentsJoinedByString" the error pops up. Does anyone have any advice or another way i can combine this array into a single NSString?
In the code you've given, there will never be an NSMutableArray for listData. At some point in your code, you'll need to create one, and presumably populate it.
Edit
Okay, so you may get into memory management problems here, so let's be a bit clearer:
You're synthesizing getters and setters for the instance variable, so it's good practice to use those to access it, they'll take care of retain and releasing appropriately.
To set listData you can simply use
self.listData = [listManage getList:[[NSUserDefaults standardUserDefaults] stringForKey:#"list_name"] list:#"LIST"];
or
[self setListData:[listManage getList:[[NSUserDefaults standardUserDefaults] stringForKey:#"list_name"] list:#"LIST"]];
if you prefer.
I have an Array of NSDictionary objects.
These Dictionaries are parsed from a JSON file.
All value objects in the NSDictionary are of type NSString, one key is called "distanceInMeters".
I had planned on filtering these arrays using an NSPredicate, so I started out like this:
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"(distanceInMeters <= %f)", newValue];
NSArray *newArray = [oldArray filteredArrayUsingPredicate:predicate];
I believe this would have worked if the value for the "distanceInMeters" key was an NSNumber, but because I have it from a JSON file everything is NSStrings.
The above gives this error:****** -[NSCFNumber length]: unrecognized selector sent to instance 0x3936f00***
Which makes sense as I had just tried to treat an NSString as an NSNumber.
Is there a way to cast the values from the dictionary while they are being filtered, or maybe a completely different way of getting around this?
Hope someone can help me :)
Try this:
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"(distanceInMeters.floatValue <= %f)", newValue];
Your problem isn't the predicate; your problem is that you're dealing with NSString objects instead of dealing with NSNumber objects. I would focus my time on changing them to NSNumbers first, and then verify that it's not working.
FYI, the JSON Framework does automatic parsing of numbers into NSNumbers...