XML Reader

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.IO;
using System.Windows.Forms;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Xml.Linq;
using System.Text.RegularExpressions;

namespace WWI_Auslesen
{
    public partial class MainWindow : Window
    {

        public MainWindow()
        {
            InitializeComponent();

        }

        public RichTextBoxScrollBars ScrollBars { get; set; }
        private void Choose_File(object sender, RoutedEventArgs e)
        {
            OpenFileDialog fileDialog = new OpenFileDialog();
            StringBuilder sb = new StringBuilder();

            fileDialog.Multiselect = true;
            fileDialog.Filter = "WWI Files|*.wwi|XML Files|*.xml";
            fileDialog.DefaultExt = "*.wwi";

            DialogResult result = fileDialog.ShowDialog();

            if (result == System.Windows.Forms.DialogResult.OK)
            {
                string[] xmlTextLines = File.ReadAllLines(fileDialog.FileName);
                foreach (var line in xmlTextLines)
                {
                    if (string.IsNullOrWhiteSpace(line))
                        continue;
                    string timeIdentifier = line.Contains("S:<") ? "S:<" : "R:<";
                    string timeString = line.Substring(0, line.IndexOf(timeIdentifier));
                    string xmlString = line.Substring(line.IndexOf(timeIdentifier) + 2);
                    xmlString = XDocument.Parse(xmlString).ToString();
                    sb.Append(timeString);
                    sb.AppendLine(timeIdentifier.Remove(timeIdentifier.Length - 1, 1));
                    sb.AppendLine(xmlString);
                    sb.AppendLine();
                    RichTextBox1.AppendText(sb.ToString());

                }
            }
        }

        private void richtextBox1_PreviewDrop(object sender, System.Windows.DragEventArgs e)
        {
            StringBuilder sb = new StringBuilder();
            string[] fileloadup = (string[])e.Data.GetData(System.Windows.DataFormats.FileDrop);
            string[] xmlTextLines = File.ReadAllLines(fileloadup[0]);
            foreach (var line in xmlTextLines)
            {
                if (string.IsNullOrWhiteSpace(line))
                    continue;
                string timeIdentifier = line.Contains("S:<") ? "S:<" : "R:<";
                string timeString = line.Substring(0, line.IndexOf(timeIdentifier));
                string xmlString = line.Substring(line.IndexOf(timeIdentifier) + 2);
                xmlString = XDocument.Parse(xmlString).ToString();
                sb.Append(timeString);
                sb.AppendLine(timeIdentifier.Remove(timeIdentifier.Length - 1, 1));
                sb.AppendLine(xmlString);
                sb.AppendLine();
                RichTextBox1.AppendText(sb.ToString());
            }
            e.Handled = true;
        }

        private void richtextBox1_PreviewDragOver(object sender, System.Windows.DragEventArgs e)
        {
            e.Effects = System.Windows.DragDropEffects.All;
            e.Handled = true;
        }
        private void Cancel(object sender, RoutedEventArgs e)
        {
            this.Close();
        }

        private void Button_Search(object sender, RoutedEventArgs e)
        {
            TextRange textRange = new TextRange(RichTextBox1.Document.ContentStart, RichTextBox1.Document.ContentEnd);
            textRange.ClearAllProperties();
            lbl_Status.Content = "";
            string textBoxText = textRange.Text;
            string searchText = userInput.Text;

            if (string.IsNullOrWhiteSpace(textBoxText) || string.IsNullOrWhiteSpace(searchText))
            {
                lbl_Status.Content = "Bitte erst eine Datei wählen!";
            }
            else
            {
                Regex regex = new Regex(searchText);
                int count_MatchFound = Regex.Matches(textBoxText, regex.ToString()).Count;

                for (TextPointer startPointer = RichTextBox1.Document.ContentStart;
                                startPointer.CompareTo(RichTextBox1.Document.ContentEnd) <= 0;
                                    startPointer = startPointer.GetNextContextPosition(LogicalDirection.Forward))
                {
                    if (startPointer.CompareTo(RichTextBox1.Document.ContentEnd) == 0)
                    {
                        break;
                    }
                    string parsedString = startPointer.GetTextInRun(LogicalDirection.Forward);
                    int indexOfParseString = parsedString.IndexOf(searchText);
                    if (indexOfParseString >= 0)
                    {
                        startPointer = startPointer.GetPositionAtOffset(indexOfParseString);

                        if (startPointer != null)
                        {
                            TextPointer nextPointer = startPointer.GetPositionAtOffset(searchText.Length);
                            TextRange searchedTextRange = new TextRange(startPointer, nextPointer);
                            searchedTextRange.ApplyPropertyValue(TextElement.BackgroundProperty, new SolidColorBrush(Colors.Yellow));
                        }
                    }
                }
                if (count_MatchFound > 0)
                {
                    lbl_Status.Content = "Erzielte Treffer: " + count_MatchFound;
                }
                else
                {
                    lbl_Status.Content = "Kein Treffer erzielt!";
                }
            }
        }

        private void WatermarkedTxt_GotFocus(object sender, RoutedEventArgs e)
        {
            watermarkedTxt.Visibility = System.Windows.Visibility.Collapsed;
            userInput.Visibility = System.Windows.Visibility.Visible;
            userInput.Focus();
        }

        private void UserInput_LostFocus(object sender, RoutedEventArgs e)
        {
            if (string.IsNullOrEmpty(userInput.Text))
            {
                userInput.Visibility = System.Windows.Visibility.Collapsed;
                watermarkedTxt.Visibility = System.Windows.Visibility.Visible;
            }
        }
    }
}