修改字典值是可能的.什么是正确的方法？

Question

我有填充的字典,我无法控制.

我需要修改值我该怎么做？

我把一个简单的例子放在一起来解释这个问题

class Program
{
    static void Main(string[] args)
    {


        Dictionary<Customer, int> CustomerOrderDictionary = new Dictionary<Customer, int>();

        CustomerOrderDictionary.Add(new Customer { Id = 1, FullName = "Jo Bloogs" },3);

        CustomerOrderDictionary.Add(new Customer { Id = 2, FullName = "Rob Smith" },5);

        //now I decide to increase the quantity but cannot do the below as value has no setter

        foreach (var pair in CustomerOrderDictionary)
        {
            if(pair.Key.Id==1)
            {
                pair.Value = 4;///ERROR HERE
            }
        }
    }
}


public class Customer
{
    public int Id { get; set; }
    public string FullName { get; set; }
}

有什么建议？非常感谢

Answer 1

我建议你工作了哪个键需要修改第一,然后遍历这些修改.否则,当你迭代它时,你最终会修改一个集合,这将引发异常.例如:

// The ToList() call here is important, so that we evaluate all of the query
// *before* we start modifying the dictionary
var keysToModify = CustomerOrderDictionary.Keys
                                          .Where(k => k.Id == 1)
                                          .ToList();
foreach (var key in keysToModify)
{
    CustomerOrderDictionary[key] = 4;
}

Answer 2

这里的问题是对的类型KeyValuePair是一个只读对象,不能修改.此外,该KeyValuePair集合是一种查看字典内容的方式(不更改它).

你想在这里做的只是直接修改字典.该Key在KeyValuePair可用于更新词典中的同一个条目.

if(pair.Key.Id==1) {
  CustomerOrderDictionary[pair.Key] = 4;
}

编辑

正如Jon指出的那样,赋值将使迭代器无效.最简单但无效的路线是在循环开始时复制枚举器.

foreach (var pair in CustomerOrderDictionary.ToList())