Objective-C字典初识

字典中存放的是键值对   可通过键取得值

1.创建不可变字典

//         1  f(1)
        NSDictionary * dic = [[NSDictionary alloc] initWithObjectsAndKeys:@"one",@"1",@"two",@"2",@"three",@"3", nil];
        NSLog(@"%@",dic);
        
        // 2 快速创建字典
        NSDictionary * dic2 = @{@"1":@"one",@"2":@"two",@"3":@"three"};
        NSLog(@"%@",dic2);

2.字典中的元素个数

 NSUInteger count = [dic2 count];

NSLog(@"%lu",count); 

3.字典中可以存放数组

        NSArray * arr = @[@"one",@"two",@"three"];
        NSDictionary * dic3 = @{@"1":@"one",@"array":arr,@"2":@"two"};
        NSLog(@"%@",dic3);

4.字典中取值

        // 5 从字典中取值
        NSArray * arr2 = [dic3 objectForKey:@"array"];
        NSLog(@"%@",arr2);
        // 快速取法
        NSArray * arr3 = dic3[@"array"];
        NSLog(@"%@",arr3);  

5.可变字典

　　5.1 可变字典的创建

 // 创建
        NSMutableDictionary * muDic = [[NSMutableDictionary alloc] initWithObjectsAndKeys:@"one",@"1",@"two",@"2", nil];
        
        NSDictionary * dic = @{@"1":@"one",@"2":@"two"};
        
        NSMutableDictionary * muDic2 = [[NSMutableDictionary alloc] initWithDictionary:dic];
        
        NSLog(@"%@",muDic2);

　　5.2 向字典中添加元素

        [muDic2 setObject:@"three" forKey:@"3"];
        NSLog(@"%@",muDic2);

　　5.3 重置字典（set方法）

        [muDic2 setDictionary:@{@"a":@"one",@"b":@"two"}];
        NSLog(@"%@",muDic2);

　　5.4 删除元素

　　　　删除key对应的键值对

 [muDic2 removeObjectForKey:@"a"];

NSLog(@"%@",muDic2); 

　　　　删除全部

 

2 [muDic2 removeAllObjects];

NSLog(@"%@",muDic2); 

　　5.5打印字典中的元素

        NSArray * arr = [muDic2 allKeys];
        // arr存储字典中所有的key
        NSLog(@"%@",arr);
        // 用快速枚举的方式打印字典muDic中的值
        for (NSString * str in arr) {
//            NSLog(@"%@",[muDic2 objectForKey:str]);
            NSLog(@"%@",muDic2[str]);
        }

扩展

- (BOOL)isKindOfClass:(Class)aClass; 

判断是否是某种类型    

example 

[obj isKindOfClass:[NSString class]];

判断obj是否是NSString类型 返回值为BOOL类型