Nsdictionary and nsmutabledictionary

2) nsnull Nsnull is probably the simplest class in cocoa. There is only one method. + (Nsnull *) NULL; You can add it to the collection in this way. [Contact setobject: [nsnull null] Forkey: @ "home fax machine"]; Access: Id homefax; Homefax = [contact objectforkey: @ "home fax machine"]; If (homefax = [nsnull null]) { //... No fax machine. Rats. } // [Nsnull null] always returns the same value, so you can use "=" to compare this value with other values ...... 22. nsdictionary and nsmutabledictionary A) nsdictionary A dictionary is a set of keywords and their definitions. It is also used as a hash or associated array. It uses an optimized storage method for key queries. 1) creation method: Use dictionarywithobjectsandkeys to create a dictionary. + (ID) dictionarywithobjectsandkeys: (ID) firstobject ,...; Usage: Tire * T1 = [Tire new]; Tire * t2 = [Tire new]; Tire * T3 = [Tire new]; Tire * t4 = [Tire new]; Nsdictionary * tires; Tires = [nsdictionary dictionarywithobjectsandkeys: T1, @ "front-left", T2, @ "front-Right ", T3, @ "back-left", T4, @ "back-right", nil]; 2) Common Methods -(ID) objectforkey: (ID) akey; Usage: Tire * tire = [Tires objectforkey: @ "back-right"]; // If not, the nil value is returned. B) nsmutabledictionary 1) creation method: You can send a dictionary message to a class nsmutabledictionary. You can also use the function + (ID) dictionarywithcapacity: (unsigned INT) numitems; 2) Common Methods You can use setobject: forkey: to add an element to the dictionary: -(Void) setobject: (ID) anobject forkey: (ID) akey; -(Void) removeobjectforkey: (ID) akey; Usage: Nsmutabledictionary * tires; Tires = [nsmutabledictionary dictionary]; [TIRES setobject: T1 forkey: @ "front-left"]; [TIRES setobject: T2 forkey: @ "front-Right"]; [TIRES setobject: T3 forkey: @ "back-left"]; [TIRES setobject: T4 forkey: @ "back-right"]; // If it already exists, it will replace the original value with the new value [TIRES removeobjectforkey: @ "back-left"]; 23. Do not create nsstring, nsarray, or nsdictionary subclasses, because in cocoa, many classes are actually implemented in the form of class clusters, that is, they are a group of implementation-related classes hidden under common interfaces. 24. Foundation instance // find files A) Use enumeration Traversal Int main (INT argc, const char * argv []) { NSAID utoreleasepool * pool; Pool = [[NSAID utoreleasepool alloc] init]; // Automatically releases the pool. Nsfilemanager * manager; // many classes in cocoa are single-instance architectures, that is, only one instance is required. you really only need one file manager. Manager = [nsfilemanager defaultmanager]; // The defaultmanager method creates an nsfilemanager object. Nsstring * home; Home = [@"~ "Stringbyexpandingtildeinpath]; // The stringbyexpandingtildeinpath method can be set ~ Replace with the current user's home directory Nsdirectoryenumerator * direnum; // subclass of nsenumerator Direnum = [Manager enumeratoratpath: Home]; // create an enumeration Condition Nsmutablearray * files; Files = [nsmutablearray arraywithcapacity: 42]; // store the search results as files Nsstring * filename; While (filename = [direnum nextobject]) {// when you call nextobject, the system will return another path of one file in the directory, or you can search for subdirectories. If ([[filename pathextension] // the extension of the pathextension output file (remove the preceding vertex .) Isequalto: @ "jpg"]) { [Files addobject: Filename]; } } Nsenumerator * fileenum; Fileenum = [files objectenumerator]; While (filename = [fileenum nextobject]) { Nslog (@ "% @", filename ); } [Pool drain]; Return (0 ); } // Main B) Use Quick Traversal Int main (INT argc, const char * argv []) { NSAID utoreleasepool * Pool = [[NSAID utoreleasepool alloc] init]; Nsfilemanager * manager; Manager = [nsfilemanager defamanager manager]; Nsstring * home; Home = [@"~ "Stringbyexpandingtildeinpath]; Nsmutablearray * files; Files = [nsmutablearray arraywithcapacity: 42]; For (nsstring * filename In [Manager enumeratoratpath: Home]) { If ([[filename pathextension] Isequalto: @ "jpg"]) { [Files addobject: Filename]; } } For (nsstring * filename in files ){ Nslog (@ "% @", filename ); } Berwinzheng 19:35:36