如何在Winform和WPF中读取、写入和修改记事本(.txt)文件的内容

最简单的是StreamReader和StreamWriter：

    using (var writer = new StreamWriter(@"C:'blah'somefile.txt"))
    {
        writer.WriteLine("Hello!");
    }
    using (var reader = new StreamReader(@"C:'blah'somefile.txt"))
    {
        var line = reader.ReadLine();
    }

您只需要使用System.IO.File。

class WriteTextFile
{
    static void Main()
    {
        // These examples assume a "C:'Users'Public'TestFolder" folder on your machine.
        // You can modify the path if necessary.
        // Example #1: Write an array of strings to a file.
        // Create a string array that consists of three lines.
        string[] lines = {"First line", "Second line", "Third line"};
        System.IO.File.WriteAllLines(@"C:'Users'Public'TestFolder'WriteLines.txt", lines);

        // Example #2: Write one string to a text file.
        string text = "A class is the most powerful data type in C#. Like structures, " +
                       "a class defines the data and behavior of the data type. ";
        System.IO.File.WriteAllText(@"C:'Users'Public'TestFolder'WriteText.txt", text);
        // Example #3: Write only some strings in an array to a file.
        using (System.IO.StreamWriter file = new System.IO.StreamWriter(@"C:'Users'Public'TestFolder'WriteLines2.txt"))
        {
            foreach (string line in lines)
            {
                // If the line doesn't contain the word 'Second', write the line to the file.
                if (!line.Contains("Second"))
                {
                    file.WriteLine(line);
                }
            }
        }
        // Example #4: Append new text to an existing file
        using (System.IO.StreamWriter file = new System.IO.StreamWriter(@"C:'Users'Public'TestFolder'WriteLines2.txt", true))
        {
            file.WriteLine("Fourth line");
        }  
    }
}
/* Output (to WriteLines.txt):
    First line
    Second line
    Third line
 Output (to WriteText.txt):
    A class is the most powerful data type in C#. Like structures, a class defines the data and behavior of the data type.
 Output to WriteLines2.txt after Example #3:
    First line
    Third line
 Output to WriteLines2.txt after Example #4:
    First line
    Third line
    Fourth line
 */

这是一个非常基本的主题，只需简单的搜索就已经有很多信息了。举个例子，这里有一个SO问题，应该让你开始：

如何在C#中读取和写入文件