C#正则表达式替换

String SourcePath = @"C:\demo";
var files = Directory.GetFiles(SourcePath, "*.cs", SearchOption.AllDirectories);

foreach (var filePath in files)
{
    label2.Text = "正在替换:" + filePath + "文件";
    foreach (var oldstr in s)
    {
        File.WriteAllText(filePath, Regex.Replace(File.ReadAllText(filePath), oldstr, "DALService"));
        label1.Text = "当前关键字:" + oldstr;
        Application.DoEvents();
    }
}
MessageBox.Show("替换完毕！");