IOS Singleton Mode

1. Define a static global variable static settings * sharedsettings = nil; 2. Create a class method to return the class instance + (settings *) sharedinstance {@ synchronized (Self) {If (sharedsettings = nil) {sharedsettings = [[self alloc] init]; // perform some initialization operations} return sharedsettings;} 3. Rewrite the allocwithzone method, it is used to ensure that no new instance is generated when others directly use alloc and init to obtain a new strength. + (ID) allocwithzone :( nszone *) Zone {@ synchronized (Self) {If (sharedsettings = nil) {sharedsettings = [Super allocwithzone: Zone] ;}} return sharedsettings;} 4. Implement allocwithezone, copywithzone, release, and autorelease + (ID) copywithzone :( nszone *) Zone {return self;}-(ID) Retain {return self;}-(unsigned) retaincount {return uint_max;}-(oneway void) release {}-(ID) autorelease {return self ;}