C# 如何写入文本文件？

Question

在线主题。老师给了我们这个但是没有运行。在 fileWriter.WriteLine 所在的第 48 行抛出错误 System.NullReferenceException: 'Object reference not set to an instance of an object.'

在线教程看起来完全不同

    public partial class frmMain : Form
    {
        private StreamWriter fileWriter;

        public class Record
        {
            public string Name { get; set; }
            public string ID { get; set; }
            public string Suburb { get; set; }
            public decimal Fee { get; set; }

        }

        string fileName = "student.txt";


        private void frmMain_Load(object sender, EventArgs e)
        {

            FileStream output = new FileStream(fileName,
                FileMode.OpenOrCreate, FileAccess.Write);

            fileWriter = new StreamWriter(output);
        }
        private void btnSave_Click(object sender, EventArgs e)
        {
            Record record = new Record();

            record.Name = txtName.Text;
            record.ID = txtID.Text;
            record.Suburb = txtSuburb.Text;
            record.Fee = Convert.ToDecimal(txtFee.Text);

            fileWriter.WriteLine(record.Name + "," + record.ID + "," +
                record.Suburb + "," + record.Fee); // Error here


            txtName.Text = "";
            txtID.Text = "";
            txtSuburb.Text = "";
            txtFee.Text = "";
        }

    }

Answer 1

你的frmMain_Load没有连接上，点击IDE属性中的加载事件，select那个方法。

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