IOS Singleton

2014-06-22 Kommentare Design Pattern

參考來源：

目前的宣告方式
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MyClass *sharedInstance;

+(MyClass*) sharedInstance{
    if(sharedInstance == nil){
        sharedInstance = [MyClass new];
    }

    return sharedInstance;
}
使用GCD dispatch方式
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+(SchoolManager *)sharedInstance
{
    static SchoolManager *sharedManager;

    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        sharedManager = [[SchoolManager alloc] init];
    });

    return sharedManager;
}
不使用GCD的方式
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//Non-GCD based code
+ (id)sharedManager {
    static MyManager *sharedMyManager = nil;
    @synchronized(self) {
        if (sharedMyManager == nil)
            sharedMyManager = [[self alloc] init];
    }
    return sharedMyManager;
}
非ARC方式
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#import "MyManager.h"

static MyManager *sharedMyManager = nil;

@implementation MyManager

@synthesize someProperty;

#pragma mark Singleton Methods
+ (id)sharedManager {
  @synchronized(self) {
      if(sharedMyManager == nil)
          sharedMyManager = [[super allocWithZone:NULL] init];
  }
  return sharedMyManager;
}
+ (id)allocWithZone:(NSZone *)zone {
  return [[self sharedManager] retain];
}
- (id)copyWithZone:(NSZone *)zone {
  return self;
}
- (id)retain {
  return self;
}
- (unsigned)retainCount {
  return UINT_MAX; //denotes an object that cannot be released
}
- (oneway void)release {
  // never release
}
- (id)autorelease {
  return self;
}
- (id)init {
  if (self = [super init]) {
      someProperty = [[NSString alloc] initWithString:@"Default Property Value"];
  }
  return self;
}
- (void)dealloc {
  // Should never be called, but just here for clarity really.
  [someProperty release];
  [super dealloc];
}

@end
#Design Pattern #IOS #Singleton