字典：NSDictionary-回忆

字典就是关键字及其定义（描述）的集合。Cocoa中的实现字典的集合NSDictionary在给定的关键字（通常是一个NSString）下存储一个数值（可以是任何类型的对象）。然后你就可以用这个关键字来查找相应的数值。

不同于数组，字典（也被称为散列表或关联数组）使用的是键查询的优化存储方式。它可以立即找出要查询的数据，而不需要遍历整个数组进行查找。

可使用dictionaryWithObjectsAndKeys来创建字典

查询字典的值：objectForKey

NSMutableDictionary的dictionary方法可以创建一个可变字典，也可以使用dictionaryWithCapaticy：。

使用 setObject:forkey: 方法添加字典元素，如果关键字已存在，则用新植替换旧值。

类似的，NSMutableDictionary类允许随意添加或删除字典元素。

添加元素：setObject:forkey:

删除元素：removeObjectForKey:

Example:

1 //

2 // MyClass.h

3 // FoundationKit4

4 //

5 // Created by Elf Sundae on 10/22/10.

6 // Copyright 2010 Control-Strength. All rights reserved.

7 //

8

9 #import <Cocoa/Cocoa.h>

10

11

12 @interface MyClass : NSObject

13 {

14 NSString *firstName;

15 NSString *lastName;

16 }

17

18

19 - (void)
setFirstName:(NSString *)m_firstName;

20 - (NSString *)
firstName;

21

22 - (void)
setLastName: (NSString *) m_lastName;

23 - (NSString *)
lastName;

24

25

26 @end

1 //

2 // MyClass.m

3 // FoundationKit4

4 //

5 // Created by Elf Sundae on 10/22/10.

6 // Copyright 2010 Control-Strength. All rights reserved.

7 //

8

9 #import "MyClass.h"

10

11

12 @implementation MyClass

13

14 - (void)
setFirstName:(NSString *)m_firstName{

15

16 firstName = m_firstName;

17 }

18 - (NSString *)
firstName{

19
return firstName;

20 }

21

22 - (void)
setLastName: (NSString *) m_lastName{

23 lastName = m_lastName;

24 }

25 - (NSString *)
lastName{

26
return lastName;

27 }

28

29

30 - (NSString *)
description

31 {

32
if (firstName == nil || lastName == nil)
{

33
return @"No Name found.";

34 } else {

35
return [NSString stringWithFormat:@"%@ %@",

36 firstName,lastName];

37 }

38

39 }

40

41 @end

1 /*

2 * 示例字典（NSDictionary,NSMutableDictionary）操作

3 *

4 * Elf Sundae 10/22/2010

5
*/

6

7 #import <Foundation/Foundation.h>

8 #import "MyClass.h"

9

10 int main (int argc, const char * argv[])
{

11 NSAutoreleasePool * pool = [[NSAutoreleasePool
alloc] init];

12

13
// 创建字典：dictionaryWithObjectsAndKeys:

14 MyClass *my1 = [MyClass new];

15 MyClass *my2 = [MyClass new];

16 MyClass *my3 = [MyClass new];

17 MyClass *my4 = [MyClass new];

18

19 NSDictionary *myClassDict;

20 myClassDict = [NSDictionary
dictionaryWithObjectsAndKeys:

21 my1, @"my1",

22 my2, @"my2",

23 my3, @"my3",

24 my4, @"my4",
nil];

25
// 获取值 objectForKey

26 MyClass *sub = [myClassDict
objectForKey: @"my3"];

27
if (sub == nil) {

28 exit(1);

29 }

30 [sub setFirstName:@"Elf"];

31 [sub setLastName:@"Sundae"];

32

33 NSLog(@"修改数据：
%@",sub);

34

35
// 遍历字典

36 NSLog(@"***遍历字典myClassDict如下：");

37
for (id key in myClassDict)

38 {

39 NSLog(@"key:
%@ ,value: %@",key,[myClassDict objectForKey:key]);

40 }

41 NSLog(@"***遍历字典myClassDict结束。");

42

43
// MARK: *** 添加新元素 ***

44
// NSDictionary无法添加或删除元素，可以使用NSMutableDictionary.

45 NSMutableDictionary *myNewDict = [NSMutableDictionary
dictionary];

46
// 将原有字典添加到新字典的一对元素

47
//[myNewDict setObject:myClassDic forKey:@"旧的不可变字典myClassDic"];

48

49
// 遍历添加已有数据(原字典)

50
for (id key in myClassDict)

51 {

52 [myNewDict setObject: [myClassDict objectForKey:key]

53 forKey:key];

54 }

55

56 NSString *newkey = @"newKey";

57 NSString *newValue = @"This
is a new Value.";

58 [myNewDict setObject:newValue forKey:newkey];

59

60
// 遍历myNewDict

61 NSLog(@"***遍历字典myNewDict如下：");

62
for (id key in myNewDict)

63 {

64 NSLog(@"key:
%@ ,value: %@",key,[myNewDict objectForKey:key]);

65 }

66 NSLog(@"***遍历字典myNewDict结束。");

67

68
// 删除元素

69 [myNewDict removeObjectForKey: @"newKey"];

70

71
// 遍历myNewDict

72 NSLog(@"***遍历字典myNewDict如下：");

73
for (id key in myNewDict)

74 {

75 NSLog(@"key:
%@ ,value: %@",key,[myNewDict objectForKey:key]);

76 }

77 NSLog(@"***遍历字典myNewDict结束。");

78

79 [pool drain];

80
return 0;

81 }

// 输出结果（省略日期 时间等信息）

修改数据： Elf Sundae

***遍历字典myClassDict如下：

key: my3 ,value: Elf Sundae

key: my4 ,value: No Name found.

key: my1 ,value: No Name found.

key: my2 ,value: No Name found.

***遍历字典myClassDict结束。

***遍历字典myNewDict如下：

key: newKey ,value: This is a new Value.

key: my3 ,value: Elf Sundae

key: my4 ,value: No Name found.

key: my1 ,value: No Name found.

key: my2 ,value: No Name found.

***遍历字典myNewDict结束。

***遍历字典myNewDict如下：

key: my3 ,value: Elf Sundae

key: my4 ,value: No Name found.

key: my1 ,value: No Name found.

key: my2 ,value: No Name found.

***遍历字典myNewDict结束。