OC_08字典

这次咱们来讲讲OC中的字典。
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’一般都是‘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’。

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];        //创建一个只有一个键值对的字典      NSDictionary *dictionary3 = [NSDictionary dictionaryWithObject:@"Jack" forKey:@"name"];      //创建一个只有多个键值对的字典        NSDictionary *dictionary4 = [NSDictionary dictionaryWithObjectsAndKeys:@"Jason",@"name",@22,@"age",@"CZ",@"address", nil];//        NSLog(@"%@",dictionary4[@"name"]);        //字典里面存放的元素都要是对象类型才行。如果基本数据类型，要先把基本数据类型进行封装，然后再放到这些集合中去。        NSDictionary *dictionary5 = [NSDictionary dictionaryWithDictionary:dictionary4];        NSLog(@"%@",dictionary5);        //新语法创建字典        NSDictionary *dictionary6 = @{};        //新语法创建只有一个键值对的字典        NSDictionary *dictionary7 = @{@"name":@"Bob"};        //新语法创建有多个键值对的字典        NSDictionary *dictionary8 = @{@"name":@"Bob",@"age":@25,@"address":@"CZ"};        //从本地读取字典        NSDictionary *dictionary9 = [NSDictionary dictionaryWithContentsOfFile:@"files"];        //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"];        NSLog(@"%@",name);        //新语法        NSString *newname = dictionary4[@"name"];        NSLog(@"姓名：%@",newname);        NSLog(@"姓名：%@",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 *keysArray = dictionary4.allKeys;        NSLog(@"%@",keysArray);        NSArray *valuesArray = dictionary4.allValues;        NSLog(@"%@",valuesArray);//  使用for循环来打印 key = value   [必须记住！！！]        for (int i=0; i<dictionary4.count; i++) { //dictionary.count 键值对数量            NSLog(@"%@ = %@",dictionary4.allKeys[i],dictionary4.allValues[i]);        // 关键字 = 值  第i个关键字=第i个值 dictionary4.allKeys[i]=dictionary.allValue[i]        }        //for in        for (NSString *key in keysArray) {            NSLog(@"%@ = %@",key,dictionary4[key]);        }        //使用枚举器遍历        NSEnumerator *enumerator = [keysArray objectEnumerator];        id key;        while (key = [enumerator nextObject]) {  NSLog(@"%@ = %@",key,dictionary4[key]);        }  NSLog(@"---------------------------");  NSDictionary *dictionary = @{@"name":@"Jason",@"age":@22,@"address":@"CZ",@"name":@"Barry"}; for (NSString *str in dictionary.allKeys){    NSLog(@"%@ = %@",str,dictionary[str]); }

//注意：在字典中键值对是无序的

    //使用NSDicgtionary注意事项    /*     1.创建字典时，字典的键和数值都要是id(即对象)类型的；     2.创建字典时，传进的参数都是键值对，即键和对象要成对出现，最后不要忘了加一个nil；     3.在使用字典时，不要把字典当成可变字典使用；     4.字典的关键字(键)不要重复，如果重复了，后面的值就会覆盖前面的值。      ---[mDictionary5 setValue:@"Jason" forKey:@"name"];     ---[mDictionary5 setValue:@"Jack" forKey:@"name"];     */

---

#pragma —可变字典—
//可变字典 NSMutableDictionary

//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:@"Jack" forKey:@"name"];        //创建一个有多个键值对的可变字典        NSMutableDictionary *mDictionary3 = [NSMutableDictionary dictionaryWithObjectsAndKeys:@"Jason",@"name",@22,@"age",@"CZ",@"address", nil];        //通过另一个字典创建一个字典        NSMutableDictionary *mDictionary4 = [NSMutableDictionary dictionaryWithDictionary:mDictionary3];//        mDictionary4.allKeys;//        mDictionary4.allValues;        for (NSString *str in mDictionary3.allKeys) {            NSLog(@"%@ = %@",str,mDictionary3);        }        //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 dictionaryWithContentsOfFile:@""];        //从网络读取字典        [NSMutableDictionary dictionaryWithContentsOfURL:[NSURL URLWithString:@""] ];        //操作字典        //增        [mDictionary5 setValue:@"Jason" forKey:@"name"];        [mDictionary5 setValue:@22 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关键(键)akey对应的值)        [mDictionary5 setValue:@"Jack" forKey:@"name"];//Jack 覆盖了 Jason        //新语法        mDictionary5 [@"name"] = @"Barry";        //删        //删除指定key的对象        [mDictionary5 removeObjectForKey:@"name"];        //删除所有对象        [mDictionary5 removeAllObjects];        NSMutableDictionary *mDic8 = [NSMutableDictionary dictionaryWithObjectsAndKeys:@"Jack",@"name1",@22,@"age",@"CZ",@"address",@"Jack",@"name2",@"Jack",@"name3", nil];       NSArray *keysArray1 =  mDic8.allKeys;        for (NSString *key in keysArray1) {            NSString *string;//            NSLog(@"%@",mDic8[key]);            [mDic8[key]isKindOfClass:[NSNumber class]]; //判断mDic8[key]中的值是否为NSNumber类型        if ([mDic8[key] isKindOfClass:[NSNumber class]]) {        int age = [mDic8 [key] intValue];        mDic8[key] = [NSString stringWithFormat:@"%d",age];                NSLog(@"%d",age);        }else{                string = mDic8[key];            }     if ([string isEqualToString:@"Jack"]) {//        NSLog(@"key = %@",key);            }      NSLog(@"key = %@",key);

字典还是比较常用的一个函数。