Objective-C语法之NSDictionary和NSMutableDictionary

Java 有Map，可以把数据以键值对的形式储存起来，取值的时候通过key就可以直接拿到对应的值，方便快捷。在Objective-C语言中，词典就是做这样的事情的，和NSArray一样，一个词典对象也能保存不同类型的值，词典也分别有不可变词典和可变的词典（NSDictionary与 NSMutableDictionary），前者是线程安全的，后者不是。

PS：跟数组的区别是：词典乱序存储数据，例如通过[词典对象实例 allKeys]获取的数组对象实例是乱序的，这时需要通过[数组对象实例 sortedArrayUsingComparator:自定义排序比较器]来进一步自定义排序。

1、不可变词典NSDictionary的主要用法：

[NSDictionary dictionaryWithObjectsAndKeys:..] : 使用键值对直接创建词典对象，结尾必需使用nil标志结束。

[dictionary count]: 得到词典的键值对数量。
[dictionary keyEnumerator]: 将词典的所有key储存在NSEnumerator中，乱序；类似于Java语言中的迭代器。
[dictionary objectEnumerator]: 将词典的所有value储存在NSEnumerator中；乱序。
[dictionary objectForKey:key]: 通过传入key对象可以拿到当前key对应储存的值。

2、可变的词典NSMutableDictionary。

NSMutableDictionary是NSDictionary的子类，所以继承了NSDictionary的方法, 以上的代码对NSMutableDictionary来说完全可用。我们试试不一样的地方

增删键值数据。

[dictionary setObject: forKey:] :向可变的词典动态的添加数据 
[dictionary removeAllObjects..] : 删除掉词典中的所有数据。
[dictionary removeObjectForKey..] :删除掉词典中指定key的数据

代码示例：

main.m

#import <Foundation/Foundation.h>
/**
 NSDictionary 不可变词典，NSEnumerator对应的Value(objectEnumerator)/Key(keyEnumerator)枚举器是乱序的
 */
void testDictionary() {
    NSDictionary *dictionary = [NSDictionary dictionaryWithObjectsAndKeys:@"某某人", @"ChineseName", @"KK", @"EnglishName", @"18", @"Age", nil]; //Value and Key, don't ignore match case
    NSLog(@"[dictionary count]=%d", (int)[dictionary count]);
    
    NSEnumerator *enumeratorKey = [dictionary keyEnumerator];
    for (NSObject *obj in enumeratorKey) {
        NSLog(@"dictionary Key=%@, Value=%@", obj, [dictionary objectForKey:obj]);
    }
    
    NSEnumerator *enumeratorValue = [dictionary objectEnumerator];
    for (NSObject *obj in enumeratorValue) {
        NSLog(@"dictionary Value=%@", obj);
    }
    
    //进行根据Key的降序排序
    NSArray *array = [dictionary allKeys];
    array = [array sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
        return [obj1 compare:obj2] == NSOrderedDescending; //obj1是从最后的数组元素开始；最终结果是A-Z，1-9；相当于实际的升序排序
    }];
    for (NSObject *obj in array) {
        NSLog(@"dictionary Key=%@, Value=%@", obj, [dictionary objectForKey:obj]);
    }
}
/**
 NSMutableDictionary 可变词典，NSEnumerator对应的Value(objectEnumerator)/Key(keyEnumerator)枚举器是乱序的
 */
void testMutableDictionary() {
    NSMutableDictionary *dictionary2 = [NSMutableDictionary dictionaryWithObjectsAndKeys:@"某某人", @"ChineseName", @"KK", @"EnglishName", @"18", @"Age", nil]; //Value and Key, don't ignore match case
    [dictionary2 setObject:@"Male" forKey:@"Gender"];
    NSLog(@"[dictionary2 count]=%d", (int)[dictionary2 count]);
    
    NSEnumerator *enumeratorKey = [dictionary2 keyEnumerator];
    for (NSObject *obj in enumeratorKey) {
        NSLog(@"dictionary2 Key=%@, Value=%@", obj, [dictionary2 objectForKey:obj]);
    }
    
    NSEnumerator *enumeratorValue = [dictionary2 objectEnumerator];
    for (NSObject *obj in enumeratorValue) {
        NSLog(@"dictionary2 Value=%@", obj);
    }
    
    [dictionary2 removeObjectForKey:@"EnglishName"];
    NSLog(@"[dictionary2 count]=%d, after the operation of removeObjectForKey", (int)[dictionary2 count]);
    
    [dictionary2 removeAllObjects];
    NSLog(@"[dictionary2 count]=%d, after the operation of removeAllObjects", (int)[dictionary2 count]);
}
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        testDictionary();
        
        testMutableDictionary();
    }
    return 0;
}

结果：

2015-03-16 00:36:41.146 OCNSDictionary[787:35149] [dictionary count]=3
2015-03-16 00:36:41.150 OCNSDictionary[787:35149] dictionary Key=EnglishName, Value=KK
2015-03-16 00:36:41.150 OCNSDictionary[787:35149] dictionary Key=Age, Value=18
2015-03-16 00:36:41.150 OCNSDictionary[787:35149] dictionary Key=ChineseName, Value=某某人
2015-03-16 00:36:41.150 OCNSDictionary[787:35149] dictionary Value=KK
2015-03-16 00:36:41.151 OCNSDictionary[787:35149] dictionary Value=18
2015-03-16 00:36:41.151 OCNSDictionary[787:35149] dictionary Value=某某人
2015-03-16 00:36:41.151 OCNSDictionary[787:35149] dictionary Key=Age, Value=18
2015-03-16 00:36:41.151 OCNSDictionary[787:35149] dictionary Key=ChineseName, Value=某某人
2015-03-16 00:36:41.151 OCNSDictionary[787:35149] dictionary Key=EnglishName, Value=KK
2015-03-16 00:36:41.151 OCNSDictionary[787:35149] [dictionary2 count]=4
2015-03-16 00:36:41.151 OCNSDictionary[787:35149] dictionary2 Key=Age, Value=18
2015-03-16 00:36:41.151 OCNSDictionary[787:35149] dictionary2 Key=Gender, Value=Male
2015-03-16 00:36:41.151 OCNSDictionary[787:35149] dictionary2 Key=EnglishName, Value=KK
2015-03-16 00:36:41.152 OCNSDictionary[787:35149] dictionary2 Key=ChineseName, Value=某某人
2015-03-16 00:36:41.158 OCNSDictionary[787:35149] dictionary2 Value=18
2015-03-16 00:36:41.159 OCNSDictionary[787:35149] dictionary2 Value=Male
2015-03-16 00:36:41.159 OCNSDictionary[787:35149] dictionary2 Value=KK
2015-03-16 00:36:41.159 OCNSDictionary[787:35149] dictionary2 Value=某某人
2015-03-16 00:36:41.160 OCNSDictionary[787:35149] [dictionary2 count]=3, after the operation of removeObjectForKey
2015-03-16 00:36:41.160 OCNSDictionary[787:35149] [dictionary2 count]=0, after the operation of removeAllObjects