AvalonDock and MVVM

using System;

namespace SampleApp.ViewModels
{
    /// <summary>
    /// View-model for the 'Document Overview' pane.
    /// </summary>
    public sealed class DocumentOverviewPaneViewModel : AbstractPaneViewModel
    {
        /// <summary>
        /// The number of lines in the file.
        /// </summary>
        private int lineCount = 0;

        /// <summary>
        /// The word count in the file.
        /// </summary>
        private int wordCount = 0;

        public DocumentOverviewPaneViewModel(MainWindowViewModel mainWindowViewModel)
        {
            if (mainWindowViewModel == null)
            {
                throw new ArgumentNullException("mainWindowViewModel");
            }

            this.MainWindowViewModel = mainWindowViewModel;
            this.MainWindowViewModel.ActiveDocumentChanged += new EventHandler<EventArgs>(MainWindowViewModel_ActiveDocumentChanged);
        }

        /// <summary>
        /// Get the name of the active file.
        /// </summary>
        public string FileName
        {
            get
            {
                if (this.MainWindowViewModel.ActiveDocument == null)
                {
                    return string.Empty;
                }

                return this.MainWindowViewModel.ActiveDocument.FileName;
            }
        }

        /// <summary>
        /// Get the path of the directory that contains the active file.
        /// </summary>
        public string DirectoryPath
        {
            get
            {
                if (this.MainWindowViewModel.ActiveDocument == null)
                {
                    return string.Empty;
                }

                return this.MainWindowViewModel.ActiveDocument.DirectoryPath;
            }
        }

        /// <summary>
        /// Gets the number of lines in the file.
        /// </summary>
        public int LineCount
        {
            get
            {
                return lineCount;
            }
        }

        /// <summary>
        /// Gets the word count in the file.
        /// </summary>
        public int WordCount
        {
            get
            {
                return wordCount;
            }
        }

        /// <summary>
        /// View-model for main window.
        /// </summary>
        private MainWindowViewModel MainWindowViewModel
        {
            get;
            set;
        }

        /// <summary>
        /// Event raised when the active document in the main window's view model has changed.
        /// </summary>
        private void MainWindowViewModel_ActiveDocumentChanged(object sender, EventArgs e)
        {
            ComputeWordAndLineCount();

 	        OnPropertyChanged("FileName");
            OnPropertyChanged("DirectoryPath");
            OnPropertyChanged("LineCount");
            OnPropertyChanged("WordCount");
        }

        /// <summary>
        /// Parse the active file and compute word and line counts.
        /// </summary>
        private void ComputeWordAndLineCount()
        {
            wordCount = 0;
            lineCount = 0;

            if (this.MainWindowViewModel.ActiveDocument == null)
            {
                // Nothing to do.
                return;
            }

            string fileText = this.MainWindowViewModel.ActiveDocument.Text;
            int pos = 0;
            bool word = false;

            while (pos < fileText.Length)
            {
                if (fileText[pos] == '\n')
                {
                    ++lineCount;
                }

                if (Char.IsWhiteSpace(fileText[pos]))
                {
                    if (word)
                    {
                        ++wordCount;
                        word = false;
                    }
                }
                else
                {
                    if (!word)
                    {
                        word = true;
                    }
                }

                ++pos;
            }

            if (word)
            {
                ++wordCount;
            }
        }
    }
}