How to solve Object reference not set to an instance of an object.?

2018-06-09 08:12:22

This question already has an answer here:

What is a NullReferenceException, and how do I fix it? 33 answers

您需要首先初始化列表：

protected List<string> list = new List<string>();

I think you just need;

List<string> list = new List<string>();
list.Add("hai");

There is a difference between

List<string> list;

and

List<string> list = new List<string>();

When you didn't use new keyword in this case, your list didn't initialized. And when you try to add it hai , obviously you get an error.

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