objective-c dictionary

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dictionary是由键-对象组成的数据集合。正如在词典中查找单词的定义一样，可通过对象的键从objective-c词典中获取所需的值。

词典中的键必须是单值的，尽管它们通常是字符串，但还可以是任何对象类型。和键关联的值可以是任何对象类型，但它们不能为nil。

下面是一个使用词典的类:

 1 #import <Foundation/NSDictionary.h>
 2 #import <Foundation/NSObject.h>
 3 #import <Foundation/NSString.h>
 4 #import <Foundation/NSAutoreleasePool.h>
 5 
 6 int main(int argc, const char *argv[])
 7 {
 8     NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
 9 
10 
11 
12     //immutable dictionary
13     NSDictionary *tires = [NSDictionary  dictionaryWithObjectsAndKeys :
14                             @"front-left",@"t1" , @"front-right",@"t2" ,
15                             @"back-left",@"t3" , @"back-right",@"t4" ,nil];
16 
17     //display immutable dictionary
18     NSLog(@"t1: %@",[tires objectForKey: @"t1"]);
19     NSLog(@"t2: %@",[tires objectForKey: @"t2"]);
20     NSLog(@"t3: %@",[tires objectForKey: @"t3"]);
21     NSLog(@"t4: %@",[tires objectForKey: @"t4"]);
22 
23     //mutable dictionary
24     NSMutableDictionary *glossary = [NSMutableDictionary dictionary];
25 
26     //Store three entries in the glossary
27 //use setObject:forKey: method to set key/value
28     [glossary setObject: @"A class defined so other classes can inherit from it"
29                  forKey: @"abstract class"];
30     [glossary setObject: @"To implment all the methods defined in a protocol"
31                  forKey: @"adopt"];
32     [glossary setObject: @"Storing an object for later use"
33                  forKey: @"archiving"];
34 
35     //Retrieve and display them
36 //use objectForKey:key method to retrieve the value
37     NSLog(@"abstract class: %@",[glossary objectForKey: @"abstract class"]);
38     NSLog(@"adopt: %@",[glossary objectForKey: @"adopt"]);
39     NSLog(@"archiving: %@",[glossary objectForKey: @"archiving"]);
40 
41     [pool drain];
42     return 0;
43 
44 }