How to read file when its date modified is change?

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C#4.0

Hey everyone,
I have one folder which has one csv file. I want to read this file when it is modified or update, I want to create loop that it waits for file update and when file update i.e. its date modified changes , quickly read that file. and again wait.

Is that possible?

I written following code but it does not work proper. Correct me.Thank you.

private void button1_Click(object sender, EventArgs e)
{
    for (int p = 0; p >= 0; p++)
    {
        DateTime dt = File.GetLastWriteTime(filepath);
        DateTime date = File.GetCreationTime(filepath);

        if (File.Exists(filepath))
        {
            if (date != dt)
            {
                task();
            }
        }
    }
}

public void task()
{
    using (FileStream fs = new     FileStream(filepath,FileMode.Open,FileAccess.Read))
    {
        using (StreamReader sr = new StreamReader(fs))
        {
            string[] line = sr.ReadLine().Split(',');
          textBox1.Text = "File update"+ Environment.NewLine;
        }
    }
}