将引用类型的dictionary值设置为null的正确方法是什么

Question

让我们假设我们有一个如下的类：-

class DoubleLinkedListNode
{
public int Value { get; set; }
public DoubleLinkedListNode(int value)
{
Value = value;
}
public DoubleLinkedListNode next = null;
public DoubleLinkedListNode prev = null;
}

然后我们创建一个字典，如下所示：-

IDictionary<int, DoubleLinkedListNode> dict = new Dictionary<int, DoubleLinkedListNode>();

字典的key将保存它包含的DoubleLinkedListNode的Value，如下所示：-

DoubleLinkedListNode newNode = new DoubleLinkedListNode(value);
dict.Add(newNode.Value, newNode );

让我们还创建一个函数，该函数将字典值的类型作为输入，并在函数体中设置值null，如下所示：-

private void RemoveNode(DoubleLinkedListNode nodeToBeRemoved)
{
if(nodeToBeRemoved != null)
{
//Do Something
nodeToBeRemoved = null;
}
}

我们这样调用函数：-

RemoveNode(dict[someValue]);

让我们创建另一个函数，在该函数中，我们显式地设置值null，如下所示：-

private void RemoveNodeAnother(DoubleLinkedListNode nodeToBeRemoved)
{
if(nodeToBeRemoved != null)
{
//Do Something
dict[nodeToBeRemoved.Value] = null;
}
}

然后我们调用这样的函数：-

RemoveNodeAnother(dict[someValue]);

以上两种功能之间的区别是什么？

我问这个问题的原因是我在Leetcode上做这个问题。我写的解决方案如下：-

public class FirstUnique 
{
private class DoubleLinkedListNode
{
public int Value { get; set; }
public DoubleLinkedListNode(int value)
{
Value = value;
}
public DoubleLinkedListNode next = null;
public DoubleLinkedListNode prev = null;
}
DoubleLinkedListNode dummyHeadNode = new DoubleLinkedListNode(-1);
DoubleLinkedListNode dummyTailNode = new DoubleLinkedListNode(-1);
IDictionary<int, DoubleLinkedListNode> dict = new Dictionary<int, DoubleLinkedListNode>();
public FirstUnique(int[] nums) 
{
InitialiseDummyHeadAndTailNodes();
foreach(int i in nums)
{
Add(i);
}
}
public int ShowFirstUnique() 
{
return dummyHeadNode.next.Value;
}
public void Add(int value)
{
if (dict.ContainsKey(value))
{
RemoveNode(dict[value]);
}
else
{
DoubleLinkedListNode newNode = new DoubleLinkedListNode(value);
AddNode(newNode);
}
}
private void InitialiseDummyHeadAndTailNodes()
{
dummyHeadNode.next = dummyTailNode;
dummyTailNode.prev = dummyHeadNode;
}
private void RemoveNode(DoubleLinkedListNode nodeToBeRemoved)
{
if(nodeToBeRemoved != null)
{
nodeToBeRemoved.prev.next = nodeToBeRemoved.next;
nodeToBeRemoved.next.prev = nodeToBeRemoved.prev;
// If I write nodeToBeRemoved = null, the solution won't pass.
// But if I write dict[nodeToBeRemoved.Value] = null, the solution is accepted.
dict[nodeToBeRemoved.Value] = null;
}
}
private void AddNode(DoubleLinkedListNode nodeToBeAdded)
{
//Update the pointers.
nodeToBeAdded.prev = dummyTailNode.prev;
nodeToBeAdded.prev.next = nodeToBeAdded;
nodeToBeAdded.next = dummyTailNode;
dummyTailNode.prev = nodeToBeAdded;
//Add the node to the dictionary.
dict.Add(nodeToBeAdded.Value, nodeToBeAdded);
}
}

我已经在异常之处发表了评论。这种行为的原因可能是什么？

Answer 1

只有一种方法可以"将字典值设置为null"-

dictionary[key] = null;

事实上，若密钥不在那个里，你们需要先添加它。。。这导致将值设置为null的方法-

if (dictionary.ContainsKey(key)) 
dictionary[key] = null;
else
dictionary.Add(key, null);

请注意，将值设置为null对之前存储的内容没有任何影响。