字典 存储的内存不是连续的,用key和value进行对应(键值对) kvc 键值编码. 特点:取出的 key value 是无序的

//单元素字典 value key

        NSDictionary *dict1 = [NSDictionary dictionaryWithObject:@"1" forKey :@"a"];

        NSLog(@"dict1 =%@",dict1);

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//多元素字典 value key

        NSDictionary *dict2 = [NSDictionary dictionaryWithObjects:[NSArray arrayWithObjects:@"1",@"2",@"3",@"4",@"5",nil] forKeys:[NSArray                                      arrayWithObjects:@"a",@"b",@"c",@"d",@"e",nil]];

        NSLog(@"dict2 =%@",dict2);

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//简便写法  key value

        NSDictionary *dict3 = @{@"1":@"刘备",@"2":@"关羽",@"3":@"张飞"};

        NSLog(@"dict3 = %@",dict3);

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//取字典长度

        int count2 = (int)[dict2count];

        NSLog(@"count2 =%d",count2);

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//通过 key 取value

        NSString*value = [dict2valueForKey:@"a"];

        NSLog(@"value =%@",value);

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//通过value 取key

        NSString*value2 = [dict2objectForKey:@"d"];

        NSLog(@"value2= %@",value2);

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//取字典中所有值

        NSArray*dictValue = [dict2allValues];

        NSLog(@"dictValue =%@",dictValue);

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//取字典中所有key

        NSArray*dictKey = [dict2allKeys];

        NSLog(@"dictKey =%@",dictKey);

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//取出数组中key对应的value ,如果没找到对应的value 则使用默认值

        NSArray *dictKey2 = [dict2 objectsForKeys:[NSArray arrayWithObjects:@"a",@"b",@"z",nil] notFoundMarker:@"not fount"];

        NSLog(@"dictKey2 =%@",dictKey2);

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//迭代器

        NSEnumerator*enumerator = [dict2keyEnumerator];

        idkey =nil;

        while(key = [enumeratornextObject]) {

            NSLog(@"enumeratot key =%@",key);

        }

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//block 方式

        [dict2enumerateKeysAndObjectsUsingBlock:^(id  _Nonnullkey,id  _Nonnullobj,BOOL*_Nonnullstop) {

        }];

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