nsarray

问题 I have an NSArray formed with objects of a custom class. The class has 3 (city, state, zip) string properties. I would like to get all unique state values from the array . I did read through the NSPredicate class but couldn't make much of how to use it in this case. The only examples I could find were for string operations. Can someone please help me out? 回答1: The totally simple one liner: NSSet *uniqueStates = [NSSet setWithArray:[myArrayOfCustomObjects valueForKey:@"state"]]; The trick is

问题 This array convenience method takes a comma-separated list of objects ending with nil . myArray = [NSArray arrayWithObjects:aDate, aValue, aString, nil]; What is the purpose of the nil ? 回答1: Null terminated variable argument lists , or va_list s, keep walking the list of arguments until they encounter a placeholder or sentinel, which is nil . Since the method has no way of knowing how many arguments you are passing, it needs the sentinel ( nil ) to tell where the list ends. 回答2: To mark the

问题 Is there any way to create a new NSString from a format string like @"xxx=%@, yyy=%@" and a NSArray of objects? In the NSSTring class there are many methods like: - (id)initWithFormat:(NSString *)format arguments:(va_list)argList - (id)initWithFormat:(NSString *)format locale:(id)locale arguments:(va_list)argList + (id)stringWithFormat:(NSString *)format, ... but non of them takes a NSArray as an argument, and I cannot find a way to create a va_list from a NSArray... 回答1: It is actually not

问题 I have an array with custom objects. Each array item has a field named "name". Now I want to remove duplicate entries based on this name value. How should I go about achieving this. Thanks in advance. 回答1: You might have to actually write this filtering method yourself: @interface NSArray (CustomFiltering) @end @implementation NSArray (CustomFiltering) - (NSArray *) filterObjectsByKey:(NSString *) key { NSMutableSet *tempValues = [[NSMutableSet alloc] init]; NSMutableArray *ret =

问题 I am trying to sort an array of managed objects alphabetically. The attribue that they need to be sorted by is the name of the object (NSString) with is one of the managed attributes. Currently I am putting all of the names in an array of strings and then using sortedNameArray = [sortedNameArray sortedArrayUsingSelector:@selector(localizedCaseInsensitiveCompare:)]; and then enumerating them back into an array with the objects. This falls apart when two names are the same so I really need to

问题 I have some data like this : 1, 111, 2, 333, 45, 67, 322, 4445 NSArray *array = [[myData allKeys]sortedArrayUsingSelector: @selector(compare:)]; If I run this code, it sorted like this: 1, 111, 2,322, 333, 4445, 45, 67, but I actually want this: 1, 2, 45, 67, 111, 322, 333, 4445 How can I implement it? thz u. 回答1: Expanding on Paul Lynch's answer, here's an example I have doing exactly this using a comparison method as a category on NSString . This code handles only the case of numbers

问题 I have a plist: <plist version="1.0"> <array> <dict> <key>name</key> <string>Alabama</string> <key>abreviation</key> <string>AL</string> <key>date</key> <string>1819</string> <key>population</key> <string>4,627,851</string> <key>capital</key> <string>Montgomery</string> <key>largestCity</key> <string>Birmingham</string> </dict> <dict> <key>name</key> <string>Alaska</string> <key>abreviation</key> <string>AK</string> <key>date</key> <string>1959</string> <key>population</key> <string>683,478<

问题 What's the usual way to store c-structures in an NSArray ? Advantages, disadvantages, memory handling? Notably, what's the difference between valueWithBytes and valueWithPointer -- raised by justin and catfish below. Here's a link to Apple's discussion of valueWithBytes:objCType: for future readers... For some lateral thinking and looking more at performance, Evgen has raised the issue of using STL::vector in C++ . (That raises an interesting issue: is there a fast c library, not unlike STL:

问题 I have an objective C class like, @interface message : NSObject { NSString *from; NSString *date; NSString *msg; } I have an NSMutableArray of instances of this message class. I want serialize all the instances in the NSMutableArray into a JSON file, using the new JSONSerialization APIs in iOS 5 SDK. How can I do this ? Is creating a NSDictionary of each key, by iterating through each instance of the elements in the NSArray ? Can someone help with code of how to solve this ? I am not able to

问题 When needing to filter an NSArray to get a subset of the items in the array returned, which method is quicker more frequently and in edge cases? 回答1: The following tests (compiled in Release mode, executed on a Mac Pro) indicate that filteredArrayUsingPredicate is slower than indexesOfObjectsPassingTest if you use a "textual" predicate, but faster if you use block-based predicate. The fasted method in my test was a simple (fast-enumeration) loop that adds all matching objects to a mutable