c# - 在 c# .net 中覆盖/删除文本文件的内容

Question

我正在制作一个将学生对象列表写入文本文件并需要保存的程序，我可以简单地覆盖文件的内容或删除内容并重写新列表。这是我经过一番搜索后尝试使用的代码，

private void saveTSMI_Click(object sender, EventArgs e)
    {
        if (lstStudNames.Items.Count != 0)
        {
            SaveFileDia.Filter = "Text Files | *.txt";
            if (SaveFileDia.ShowDialog() == DialogResult.OK)
            {
                //Clear the file 
                File.WriteAllText(SaveFileDia.FileName, string.Empty);

                //Put all the student info into a string
                foreach (Stud student in StudentList)
                {
                    StudentInfoHolder += "Name: " + student.Name + Environment.NewLine +
                    "Subject: " + student.Subject + Environment.NewLine +
                    "Age: " + student.age + Environment.NewLine +
                    "Grade: " + student.Grade + Environment.NewLine
                    + Environment.NewLine;
                }
                Clipboard.SetText(StudentInfoHolder);
                File.WriteAllText(SaveFileDia.FileName, StudentInfoHolder);
            }
        }
        else
        {
            MessageBox.Show("Nothing to save");
        }

我已经看到 File.WriteAllText() 是为了覆盖文件，但在保存程序时没有任何内容被覆盖。

Answer 1

您必须在 foreach 循环之前重置 StudentInfoHolder 类成员，或者更好的是，将本地字符串变量与 String.Format< 结合使用 方法如下:

string studentInfoHolder;

foreach (Stud student in StudentList)
{
    studentInfoHolder += 
        string.Format("Name: {0}\r\nSubject: {1}\r\nAge: {2}\r\nGrade: {3}",
                      student.Name, student.Subject, student.age, student.Grade); 
}

File.WriteAllText(SaveFileDia.FileName, studentInfoHolder);

另外，File.WriteAllText 覆盖文件内容是对的，所以这一行没有用:

File.WriteAllText(SaveFileDia.FileName, string.Empty);

更新

正如@kevin 正确指出的那样，在循环中使用 StringBuilder 而不是字符串连接更有效:

StringBuilder studentInfoHolder;

foreach (Stud student in StudentList)
{
    studentInfoHolder.AppendFormat("Name: {0}\r\nSubject: {1}\r\nAge: {2}\r\nGrade: {3}",
                                   student.Name, student.Subject, student.age, student.Grade); 
} 

File.WriteAllText(SaveFileDia.FileName, studentInfoHolder.ToString());