oc中字典的实现方法详解

一:字典的基本概念

Foundation中的字典(NSDictionary，NSMutableDictionary)是由键-值对组成的数据集合.正如,我们在字典里查找单词的定义一样.

通过key(键)，查找的对应的value(值),key通常是字符串对象,也可以是其他任意类型对象.在一个字典对象中，key的值必须是唯一的.

此外,字典对象的键和值不可以为空(nil),如果需要在字典中加入一个空值，可以加入NSNull对象

二:不可变字典-NSDictionary

1:初始化(以一个元素和多个元素进行初始化):

//以一个键值对象 进行初始化

    NSDictionary *dic=[NSDictionary dictionaryWithObject:@"卢灿小样" forKey:@"lucan"];
     NSLog(@"%@",dic);
     NSLog(@"%@",[dic objectForKey:@"lucan"]);
    //输出dic键值对个数
    NSLog(@"%d",dic.count);
    
    //用多种方法创建键值对
    NSDictionary *dic1=[NSDictionary dictionaryWithObject:@"卢灿实验2号" forKey:@"小样"];
    NSLog(@"%@",[dic1 objectForKey:@"小样"]);
    
    NSDictionary *dic2=@{@"first":@"2301",@"sec":@"2034"};
    NSDictionary *dic3=[NSDictionary dictionaryWithObjectsAndKeys:@"刘湘",@"name",@"小样",@"name1", nil];
    //输出结果
    NSLog(@"  ----%@%@",dic2,dic3);
    
   //数组把vaule和key放到一个可变数组
    NSArray *values=@[@123,@668,@345];
    NSArray *key=@[@"first",@"swcond",@"third"];
    NSDictionary *dic4=[NSDictionary dictionaryWithObject:values forKey:key];
    NSLog(@"xxxxxxxxxxxx%@",dic4);
    
    //排序
    NSArray *arry=[dic4 keysSortedByValueUsingSelector:@selector(compare:)];
    NSLog(@"+++++++%@",arry);

    //用一个现有字典对象初始化另一个新字典对象(创建可变对象)
    NSDictionary *arry1=[[NSDictionary alloc]initWithDictionary:dic4 ];
    NSLog(@"ooooooo%@",arry1);
    
    //保存对象到内容文件
    NSString *path=@"/Users/apple/Desktop/test.plist";
    [dic2 writeToFile:path atomically:YES];
    
    //从以前保存的文件读取到字典对象
    NSDictionary *data=[NSDictionary dictionaryWithContentsOfFile:path];
    NSLog(@"xxxxx%@",data);
    
    //字典的遍历key1相当于a[i]中的i，dic4就自己定义的字典
    for (id key1 in dic4) {
        id vaule=[dic4 objectForKey:key1];
        NSLog(@"qqqqqq%@%@",key,vaule);
    }
    //- (void)removeObjectForKey:(id)aKey;
    //删除键值对
    NSMutableDictionary  *dic7=[NSMutableDictionary dictionaryWithDictionary:dic2];
    [dic7 removeObjectForKey:@"sec"];
    NSLog(@"%@",dic7);
    
   // 判断key值有就替换没有就添加
    [dic7 setObject:@"3412" forKey:@"sec"];
    NSLog(@"%@",dic7);
    
    //增加dic4  字典无顺序
    [dic7 addEntriesFromDictionary:dic4];
    NSLog(@"%@",dic7);