第二十七讲：Objective-C设计模式之单例

Sian

单例，即全局变量
ThemeManager.h

1. //
2. //  ThemeManager.h
3. //  ThemeManager
4. //
5. //  Created by yusian on 14-2-1.
6. //  Copyright (c) 2014年 yusian. All rights reserved.
7. //
9. #import <Foundation/Foundation.h>
11. @interface ThemeManager : NSObject
13. @property (nonatomic, retain) NSString *name;
15. + (id) sharedThemeManager;
17. @end

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ThemeManager.m

1. //
2. //  ThemeManager.m
3. //  ThemeManager
4. //
5. //  Created by yusian on 14-2-1.
6. //  Copyright (c) 2014年 yusian. All rights reserved.
7. //
9. #import "ThemeManager.h"
11. @implementation ThemeManager
13. static ThemeManager *s;
15. + (id) sharedThemeManager {
16.     if (s == nil) {
17.         s = [[[self class] alloc] init];
18.     }
19.     return s;
20. }
22. - (id) init {
23.     if (self = [super init]) {
24.         self.name = [NSString stringWithFormat:@"Default"];
25.     }
26.     return self;
27. }
29. - (NSString *) description {
30.     return [NSString stringWithFormat:@"My name is %@",self.name];
31. }
33. - (void) dealloc {
34.     [_name release];
35.     _name = Nil;
36.     [super dealloc];
37. }
39. @end

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main.m

1. //
2. //  main.m
3. //  ThemeManager
4. //
5. //  Created by yusian on 14-2-1.
6. //  Copyright (c) 2014年 yusian. All rights reserved.
7. //
9. #import <Foundation/Foundation.h>
10. #import "ThemeManager.h"
12. int main(int argc, const char * argv[])
13. {
15.     @autoreleasepool {
16.         
17.         ThemeManager * tm = [ThemeManager sharedThemeManager];
18.         
19.         ThemeManager * tm2 = [ThemeManager sharedThemeManager];
20.                         
21.         NSLog(@"tm is %@",tm);
22.         NSLog(@"tm2 is %@",tm2);
23.         
24.         NSLog(@"tm address is  %p, tm2 address is %p",tm,tm2);
25.     }
26.     return 0;
27. }

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运行结果：

1. 2014-02-01 21:40:05.406 ThemeManager[7216:303] tm is My name is Default
2. 2014-02-01 21:40:05.408 ThemeManager[7216:303] tm2 is My name is Default
3. 2014-02-01 21:40:05.408 ThemeManager[7216:303] tm address is  0x100301c00, tm2 address is 0x100301c00
4. Program ended with exit code: 0

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Sian

典型的单例的写法：
+ (id) sharedThemeManager {
        if (s == nil) {
            s = [[[self class] alloc] init];
        }
    return s;
}
加锁的写法：

+ (id) sharedThemeManager {

    @synchronized(self){

    if (s == nil) {

        s = [[[self class] alloc] init];

    }

    }

    return s;

}

GCD的写法：

+ (id) sharedThemeManager {

    static dispatch_once_t onceToken;

    dispatch_once(&onceToken, ^{

    if (s == nil) {

        s = [[[self class] alloc] init];

    }

    });

    return s;

}

Sian

重载的几个方法写法：

+ (id) copyWithZone: (NSZone *)zone {

    return self;

}

- (id) retain {

    return self;

}

- (oneway void) release {

}

- (NSUInteger) retainCount {

    return UINT_MAX;

}

- (id) autorelease {

    return self;

}