items.add、visual studio 抛出一个错误说它有 "no usable extension"

Question

这里的行和用法适合我，主要是 item.add 是我的主要错误

OpenFileDialog openFileDialog = new OpenFileDialog();

        openFileDialog.ShowDialog();

        string filePath = openFileDialog.FileName;

        System.IO.StreamReader streamReader = new System.IO.StreamReader(filePath);
        string line = "";

        int sum = 0;
        int numberCount = 0;
        while ((line = streamReader.ReadLine()) != null)
        {
            lstNumbers.**Items.Add(line);**

            sum = sum + int.Parse(line);

            numberCount++;
        }
        fileListBox.Text = "Total Numbers are " + numberCount + Environment.NewLine + V + sum;
    }

    private static void NewMethod(string line) =>

lstNumbers.Items.Add(行); }

internal class lstNumbers
{
    internal static object Items;
}

Answer 1

一些事情，如果你使用扩展方法：

扩展方法应该Public。
您必须使用 'this' 关键字作为参数。

public static int WordCount(这个字符串 str){.....}

items.add、visual studio 抛出一个错误说它有 "no usable extension"

items.add, visual studio throws an error saying it has "no usable extension"

c#

forms

syntax

calculator

winforms