diff --git a/Demo/LineNumber/Document.swift b/Demo/LineNumber/Document.swift
index 2718169..d719288 100644
--- a/Demo/LineNumber/Document.swift
+++ b/Demo/LineNumber/Document.swift
@@ -27,6 +27,9 @@ import Cocoa
 
 class Document: NSDocument {
 
+    var viewController : ViewController?
+    var documentContent : String?
+
 	override init() {
 	    super.init()
 		// Add your subclass-specific initialization here.
@@ -50,17 +53,27 @@ class Document: NSDocument {
 		self.addWindowController(windowController)
 	}
 
+    // more information about what's happening here can be found at
+    // http://sketchytech.blogspot.com/2016/09/taming-nsdocument-and-understanding.html
 	override func data(ofType typeName: String) throws -> Data {
-		// Insert code here to write your document to data of the specified type. If outError != nil, ensure that you create and set an appropriate error when returning nil.
-		// You can also choose to override fileWrapperOfType:error:, writeToURL:ofType:error:, or writeToURL:ofType:forSaveOperation:originalContentsURL:error: instead.
-		throw NSError(domain: NSOSStatusErrorDomain, code: unimpErr, userInfo: nil)
+        // since NSDocument returns a non-optional,
+        // we should return something, even if it's nothing
+        var data = Data()
+        
+        if let rawString = self.viewController?.mainTextView.string
+        {
+            if let rawData = rawString.data(using: .utf8)
+            {
+                data = rawData
+            }
+        } else {
+            throw NSError(domain: NSOSStatusErrorDomain, code: unimpErr, userInfo: nil)
+        }
+        return data
 	}
 
 	override func read(from data: Data, ofType typeName: String) throws {
-		// Insert code here to read your document from the given data of the specified type. If outError != nil, ensure that you create and set an appropriate error when returning false.
-		// You can also choose to override readFromFileWrapper:ofType:error: or readFromURL:ofType:error: instead.
-		// If you override either of these, you should also override -isEntireFileLoaded to return NO if the contents are lazily loaded.
-		throw NSError(domain: NSOSStatusErrorDomain, code: unimpErr, userInfo: nil)
+        documentContent = String(decoding: data, as: UTF8.self)
 	}
 
 
diff --git a/Demo/LineNumber/ViewController.swift b/Demo/LineNumber/ViewController.swift
index f0c327c..debd00d 100644
--- a/Demo/LineNumber/ViewController.swift
+++ b/Demo/LineNumber/ViewController.swift
@@ -29,6 +29,10 @@ class ViewController: NSViewController {
 
 	@IBOutlet var mainTextView: NSTextView!
 	
+    var document: Document? {
+        return view.window?.windowController?.document as? Document
+    }
+
 	override func viewDidLoad() {
 		super.viewDidLoad()
 
@@ -36,10 +40,23 @@ class ViewController: NSViewController {
 		mainTextView.lnv_setUpLineNumberView()
 	}
 
+    override func viewWillAppear() {
+        super.viewWillAppear()
+        
+        if let document = self.document {
+            document.viewController = self
+            
+            if let documentContents = document.documentContent {
+                self.mainTextView.string = documentContents
+            }
+        }
+    }
+    
 	override var representedObject: Any? {
 		didSet {
 			// Update the view, if already loaded.
-			
 		}
-	}
+    }
+        
+    
 }