OC中的字典

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NSDictionary字典就是关键字（键）及其定义所构成的集合。字典在给定的关键字下存储一个数值，这个关键字（键）通常是一个NSString类型的字符串，存储的这个数值可以是Object-C里的任意类型的对象。然后你就可以使用这个关键字来找到其对应的值。

字典和数组一样，也分为不可变字典（NSDictionary）和可变字典(NSMutableDictionary)。

NSDictionary

不可变字典的创建及访问：

   /*         字典:NSDictionary  NSMutableDictionary         1.概念:字典是关键字 ‘key’及其定义的值(value)所构成的集合，即它是由key-value组成的键值对的集合。'key'一般是'NSString'类型的，'value'是OC中任意对象。对于字典来讲，我们就是通过‘key’来访问‘value’。（字典是无序的）         2.为什么在有了数组之后，还需要字典？在由大量的数据或者频繁的查找的时候，使用字典效率更高。因为字典采用键查询的优化存储方式。         */        //初始化        //创建一个空的字典        NSDictionary *dictionary1 = [[NSDictionary alloc] init];        NSDictionary *dictionary2 = [NSDictionary dictionary];        //创建只有一个键值对的字典        NSDictionary *dictionary3 = [NSDictionary dictionaryWithObject:@"Rick" forKey:@"name"];        //创建一个多个键值对的字典        NSDictionary *dictionary4 = [NSDictionary dictionaryWithObjectsAndKeys:@"Rick",@"name",@25,@"age",@"GZ",@"address", nil];        //字典里面存放的元素都要是对象类型才行。如果是基本数据类型，要先把基本数据类型进行封装，然后再放到这些集合中去。比如不能把@25换成25放到字典里去        //通过字典创建一个字典        NSDictionary *dictionary5 = [NSDictionary dictionaryWithDictionary:dictionary4];        NSLog(@"%@",dictionary5);        //使用新语法创建字典        NSDictionary *dictionary6 = @{};        //新语法创建只有一个键值对的字典,与dictionary4创建方式顺序相反        NSDictionary *dictionary7 = @{@"name":@"Rick"};        //新语法创建多个键值对的字典        NSDictionary *dictionary8 = @{@"name":@"Rick",@"age":@25,@"address":@"GZ"};        NSLog(@"%@",dictionary8);        //从本地读取文件        NSDictionary *dictionary9 = [NSDictionary dictionaryWithContentsOfFile:@"http://www.baidu.com"];        //从网络读取字典        NSDictionary *dictionary10 = [NSDictionary dictionaryWithContentsOfURL:[NSURL URLWithString:@""]];        //字典中键值对的数量        NSUInteger count = [dictionary4 count];        NSLog(@"%lu",count);        //如何访问字典        //通过key访问字典中对应的值        NSString *name = [dictionary4 objectForKey:@"name"];        //新语法        NSString *newName = dictionary4[@"name"];        //如何遍历字典中所有的key和value        //表示字典中所有的key        NSArray *keyArray = dictionary4.allKeys;        NSArray *valueArray = dictionary4.allValues;        //打印key = value，for循环//        id key,value;//        for (int i = 0; i < dictionary4.count; i++) {//            key = [keyArray objectAtIndex:i];//            value = [dictionary4 objectForKey:key];//            NSLog(@"%@:%@",key,value);//        }        for (int i = 0; i < dictionary4.count; i++) {            //注意‘[]’的使用，数组加‘[]’就是代表数组里的元素            NSLog(@"%@:%@",keyArray[i],valueArray[i]);            }        //快速枚举        for (NSString *key in keyArray) {            NSLog(@"%@:%@",key,dictionary4[key]);//?        }        //使用枚举器遍历        NSEnumerator *enumerator = [keyArray objectEnumerator];        id key;        while (key = [enumerator nextObject]) {            NSLog(@"%@:%@",key,dictionary4[key]);        }        NSDictionary *dictionary = @{@"name":@"Rick",@"age":@"25",@"address":@"GZ",@"name":@"Jack"};        for (NSString *str in dictionary.allKeys) {            NSLog(@"%@=%@",str,dictionary[str]);        }        //注意:在字典中键值对是无序的，如果有两个相同的键值对只会打印一个

NSMutableDictionary

1.可变字典的创建

  /*         NSMutableDictionary 可变字典        */         //1.初始化方式         //创建一个空的字典        NSMutableDictionary *mDictionary1 = [NSMutableDictionary dictionary];         //创建一个有一个键值对的可变字典        NSMutableDictionary *mDictionary2 = [NSMutableDictionary dictionaryWithObject:@"Rick" forKey:@"name"];        //        NSMutableDictionary *mDictionary3 = [NSMutableDictionary dictionaryWithObjectsAndKeys:@"Rick",@"name",@"age",@"25",@"address",@"GZ", nil];        //通过另一个字典创建一个字典        NSMutableDictionary *mDictionary4 = [NSMutableDictionary dictionaryWithDictionary:mDictionary3];//        mDictionary3.allKeys 访问所有键//        mDictionary3.allValues 访问所有值        //可变字典独有的初始化方法        NSMutableDictionary *mDictionary5 = [NSMutableDictionary dictionaryWithCapacity:10];        //从本地读取字典        NSMutableDictionary *mDictionary6 = [NSMutableDictionary dictionaryWithContentsOfFile:@""];        //从网络读取字典        NSMutableDictionary *mDictionary7 = [NSMutableDictionary dictionaryWithContentsOfURL:[NSURL URLWithString:@""]];

2.对可变字典的操作

 //操作字典        //增        [mDictionary5 setValue:@"Rick" forKey:@"name"];        [mDictionary5 setValue:@25 forKey:@"age"];        //改（如果原来的字典中已经有了akey这个键，那么这次新加的值就会覆盖原来的键（akey）对应的值）        [mDictionary5 setValue:@"Jack" forKey:@"name"];        mDictionary5[@"name"] = @"Leo";        //删除指定key对应的对象        [mDictionary5 removeObjectForKey:@"name"];        //删除所有对象        [mDictionary5 removeAllObjects];        //找出相同值得键，        NSMutableDictionary *mDictionary8 = [NSMutableDictionary dictionaryWithObjectsAndKeys:@"Rick",@"name",@25,@"age",@"GZ",@"address",@"Rick",@"name2",@"Rick",@"name3",nil];//        for (int i = 0; i < mDictionary8.count; i++) {//            //            if ([mDictionary8.allValues[i]  isEqual: @"Rick"]) {//                NSLog(@"%@",mDictionary8.allKeys[i]);//            }//            else if ([mDictionary8.allValues[i]  isEqual: @25]) {//                [NSString stringWithFormat:@""]//                NSLog(@"%@");//        }//        //        NSArray *keyArray1 = mDictionary8.allKeys;        for (NSString *key in keyArray1) {            NSString *string;            NSLog(@"%@",mDictionary8[key]);            //返回一个BOOL值，YES or NO            if ([mDictionary8[key] isKindOfClass:[NSNumber class]]) {                int age = [mDictionary8[key] intValue];                mDictionary8[key] = [NSString stringWithFormat:@"%d",age];            }            else{                string = mDictionary8[key];            }            if ([string isEqualToString:@"Rick"]) {                NSLog(@"key = %@",key);            }        }

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