ASP.NET Core MVC：为什么可选列表参数从不 null？

Question

I have an MVC Application and I've got an Index method in my Controller. When the Index method is called for the first time, I want the parameter that holds the resultList of a search to be null. This is because I want to handle an empty resultList differently than a non existing one.

So I tried the following:

public async Task<IActionResult> Index(List<SomeModel> resultList = null)

But whenever I start the Web App the list is empty not null. Why is this? And do I have a chance to get a list that is null?

Answer 1

I think the best way to get a resultList to null is to create another list.

 public async Task<IActionResult> Index(List<SomeModel> resultList) 
    {
        if (resultList != null)
        {
          //...
        }
        //there the result will be null,you can do your logic with this result. 
        List<UserAddress> result = null;
        //...
    }