Question

我正在创建一个程序，将学生对象列表写入文本文件并需要保存，我可以简单地覆盖文件内容或删除内容并重写新列表。这是我在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()意在覆盖文件，但保存程序时不会覆盖任何内容。

Answer 1

您必须在StudentInfoHolder循环之前重置foreach类成员，或者更好，使用本地字符串变量和String.Format方法，如下所示：

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，你是File.WriteAllText覆盖文件内容是对的，所以这一行没用：

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

<强>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());

Answer 2

尝试更多类似以下的内容。它避免了两次打开文件，以及字符串连接，这对于不可变字符串来说不是一个好主意。

// This line over-writes the file if it exists, or otherwise creates it.
using (TextWriter fileWriter = new StreamWriter(SaveFileDia.FileName, append: false))
{
    foreach (Stud student in StudentList)
    {
        fileWriter.WriteLine($"Name: {student.Name}");
        fileWriter.WriteLine($"Subject: {student.Subject}");
        fileWriter.WriteLine($"Age: {student.age}");
        fileWriter.WriteLine($"Grade: {student.Grade}");
        fileWriter.WriteLine();
    }
}

Answer 3

没有充分的理由在将其写入文件之前缓冲内存中的所有内容。通过调用File.CreateText打开文件更容易，然后将每一行写入其中，如下所示：

private void saveTSMI_Click(object sender, EventArgs e)
{
    if (lstStudNames.Items.Count == 0)
    {
        MessageBox.Show("Nothing to save");
        return;
    }

    SaveFileDia.Filter = "Text Files | *.txt";
    if (SaveFileDia.ShowDialog() != DialogResult.OK)
    {
        return;
    }


    // Create the file (overwrite if it already exists),
    // and write each student record.
    using (var outFile = File.CreateText(SaveFileDia.FileName))
    {
        foreach (Stud student in StudentList)
        {
            outFile.WriteLine("Name: " + student.Name);
            outFile.WriteLine("Subject: " + student.Subject);
            outFile.WriteLine("Age: " + student.age);
            outFile.WriteLine("Grade: " + student.Grade);
        }
    }
}

我还稍微重构了你的代码，预先颠倒了这两个测试的逻辑，以减少代码中的嵌套。

评论后更新

如果你真的想要一个包含所有内容的字符串，那么你可以修改上面的内容来轻松完成。使用StringWriter：

替换写入文件的循环

    // Create a StringWriter to hold the data, and write each line.
    using (var sWriter = new StringWriter())
    {
        foreach (Stud student in StudentList)
        {
            sWriter.WriteLine("Name: " + student.Name);
            sWriter.WriteLine("Subject: " + student.Subject);
            sWriter.WriteLine("Age: " + student.age);
            sWriter.WriteLine("Grade: " + student.Grade);
        }

        // write the data to the file
        StudentInfoHolder = sWriter.ToString();
        File.WriteAllText(SaveFileDia.FileName, StudentInfoHolder);
    }

覆盖/删除c＃.net中文本文件的内容

3 个答案:

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