NSDictionary and NSMutableDictionary

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  NSMutableDictionary *dic = [[NSMutableDictionary alloc] initWithObjectsAndKeys:@"1",@"2",@"3", @"4", @"5", @"6", nil];    [dic setValue:nil forKey:@"2"];    NSLog(@"%@", dic);// setValue forKey 当value为空时,会将那对键值对使用 removeObjectForKey方法//    setValue forKey是NSString的方法    [dic setObject:nil forKey:@"2"];    NSLog(@"%@", dic);//    setObject forKey当object为空时,会报错//    它是NSMutableDictionary的方法    return 0;}

 NSDictionary *dic = [NSDictionary dictionaryWithObject:@"1" forKey:@"name"];    NSLog(@"%@", dic);// 创建并且返回一个含有单一object和key值的字典

 NSArray *objectArr = @[@"1", @"2", @"3"];    NSArray *keyArr = @[@"4", @"5", @"6"];    NSDictionary *dic = [NSDictionary dictionaryWithObjects:objectArr forKeys:keyArr];    NSLog(@"%@", dic);//    输出结果//    4 = 1;//    5 = 2;//    6 = 3;

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