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• Benefits of Behavior Driven Development

  - by Aligned

  Originally posted on: http://geekswithblogs.net/Aligned/archive/2013/07/26/benefits-of-behavior-driven-development.aspxContinuing my previous article on BDD, I wanted to point out some benefits of BDD and since BDD is an extension of Test Driven Development (TDD), you get those as well. I’ll add another article on some possible downsides of this approach. There are many articles about the benefits of TDD and they apply to BDD. I’ve pointed out some here and copied some of the main points for each article, but there are many more including the book The Art of Unit Testing by Roy Osherove. http://geekswithblogs.net/leesblog/archive/2008/04/30/the-benefits-of-test-driven-development.aspx (Lee Brandt) Stability Accountability Design Ability Separated Concerns Progress Indicator http://tddftw.com/benefits-of-tdd/ Help maintainers understand the intention behind the code Bring validation and proper data handling concerns to the forefront. Writing the tests first is fun. Better APIs come from writing testable code. TDD will make you a better developer. http://www.slideshare.net/dhelper/benefit-from-unit-testing-in-the-real-world (from Typemock). Take a look at the slides, especially the extra time required for TDD (slide 10) and the next one of the bugs avoided using TDD (slide 11). Less bugs (slide 11) about testing and development (13) Increase confidence in code (14) Fearlessly change your code (14) Document Requirements (14) also see http://visualstudiomagazine.com/articles/2013/06/01/roc-rocks.aspx Discover usability issues early (14) All these points and articles are great and there are many more. The following are my additions to the benefits of BDD from using it in real projects for my company. July 2013 on MSDN - Behavior-Driven Design with SpecFlow Scott Allen did a very informative TDD and MVC module, but to me he is doing BDDCompile and Execute Requirements in Microsoft .NET ~ Video from TechEd 2012 Communication I was working through a complicated task that the decision tree kept growing. After writing out the Given, When, Then of the scenario, I was able tell QA what I had worked through for their initial test cases. They were able to add from there. It is also useful to use this language with other developers, managers, or clients to help make informed decisions on if it meets the requirements or if it can simplified to save time (money). Thinking through solutions, before starting to code This was the biggest benefit to me. I like to jump into coding to figure out the problem. Many times I don't understand my path well enough and have to do some parts over. A past supervisor told me several times during reviews that I need to get better at seeing "the forest for the trees". When I sit down and write out the behavior that I need to implement, I force myself to think things out further and catch scenarios before they get to QA. A co-worker that is new to BDD and we’ve been using it in our new project for the last 6 months, said “It really clarifies things”. It took him awhile to understand it all, but now he’s seeing the value of this approach (yes there are some downsides, but that is a different issue). Developers’ Confidence This is huge for me. With tests in place, my confidence grows that I won’t break code that I’m not directly changing. In the past, I’ve worked on projects with out tests and we would frequently find regression bugs (or worse the users would find them). That isn’t fun. We don’t catch all problems with the tests, but when QA catches one, I can write a test to make sure it doesn’t happen again. It’s also good for Releasing code, telling your manager that it’s good to go. As time goes on and the code gets older, how confident are you that checking in code won’t break something somewhere else? Merging code - pre release confidence If you’re merging code a lot, it’s nice to have the tests to help ensure you didn’t merge incorrectly. Interrupted work I had a task that I started and planned out, then was interrupted for a month because of different priorities. When I started it up again, and un-shelved my changes, I had the BDD specs and it helped me remember what I had figured out and what was left to do. It would have much more difficult without the specs and tests. Testing and verifying complicated scenarios Sometimes in the UI there are scenarios that get tricky, because there are a lot of steps involved (click here to open the dialog, enter the information, make sure it’s valid, when I click cancel it should do {x}, when I click ok it should close and do {y}, then do this, etc….). With BDD I can avoid some of the mouse clicking define the scenarios and have them re-run quickly, without using a mouse. UI testing is still needed, but this helps a bunch. The same can be true for tricky server logic. Documentation of Assumptions and Specifications The BDD spec tests (Jasmine or SpecFlow or other tool) also work as documentation and show what the original developer was trying to accomplish. It’s not a different Word document, so developers will keep this up to date, instead of letting it become obsolete. What happens if you leave the project (consulting, new job, etc) with no specs or at the least good comments in the code? Sometimes I think of a new scenario, so I add a failing spec and continue in the same stream of thought (don’t forget it because it was on a piece of paper or in a notepad). Then later I can come back and handle it and have it documented. Jasmine tests and JavaScript –> help deal with the non-typed system I like JavaScript, but I also dislike working with JavaScript. I miss C# telling me if a property doesn’t actually exist at build time. I like the idea of TypeScript and hope to use it more in the future. I also use KnockoutJs, which has observables that need to be called with ending (), since the observable is a function. It’s hard to remember when to use () or not and the Jasmine specs/tests help ensure the correct usage.   This should give you an idea of the benefits that I see in using the BDD approach. I’m sure there are more. It talks a lot of practice, investment and experimentation to figure out how to approach this and to get comfortable with it. I agree with Scott Allen in the video I linked above “Remember that TDD can take some practice. So if you're not doing test-driven design right now? You can start and practice and get better. And you'll reach a point where you'll never want to get back.”

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• Metro: Understanding Observables

  - by Stephen.Walther

  The goal of this blog entry is to describe how the Observer Pattern is implemented in the WinJS library. You learn how to create observable objects which trigger notifications automatically when their properties are changed. Observables enable you to keep your user interface and your application data in sync. For example, by taking advantage of observables, you can update your user interface automatically whenever the properties of a product change. Observables are the foundation of declarative binding in the WinJS library. The WinJS library is not the first JavaScript library to include support for observables. For example, both the KnockoutJS library and the Microsoft Ajax Library (now part of the Ajax Control Toolkit) support observables. Creating an Observable Imagine that I have created a product object like this: var product = { name: "Milk", description: "Something to drink", price: 12.33 }; Nothing very exciting about this product. It has three properties named name, description, and price. Now, imagine that I want to be notified automatically whenever any of these properties are changed. In that case, I can create an observable product from my product object like this: var observableProduct = WinJS.Binding.as(product); This line of code creates a new JavaScript object named observableProduct from the existing JavaScript object named product. This new object also has a name, description, and price property. However, unlike the properties of the original product object, the properties of the observable product object trigger notifications when the properties are changed. Each of the properties of the new observable product object has been changed into accessor properties which have both a getter and a setter. For example, the observable product price property looks something like this: price: { get: function () { return this.getProperty(“price”); } set: function (value) { this.setProperty(“price”, value); } } When you read the price property then the getProperty() method is called and when you set the price property then the setProperty() method is called. The getProperty() and setProperty() methods are methods of the observable product object. The observable product object supports the following methods and properties: · addProperty(name, value) – Adds a new property to an observable and notifies any listeners. · backingData – An object which represents the value of each property. · bind(name, action) – Enables you to execute a function when a property changes. · getProperty(name) – Returns the value of a property using the string name of the property. · notify(name, newValue, oldValue) – A private method which executes each function in the _listeners array. · removeProperty(name) – Removes a property and notifies any listeners. · setProperty(name, value) – Updates a property and notifies any listeners. · unbind(name, action) – Enables you to stop executing a function in response to a property change. · updateProperty(name, value) – Updates a property and notifies any listeners. So when you create an observable, you get a new object with the same properties as an existing object. However, when you modify the properties of an observable object, then you can notify any listeners of the observable that the value of a particular property has changed automatically. Imagine that you change the value of the price property like this: observableProduct.price = 2.99; In that case, the following sequence of events is triggered: 1. The price setter calls the setProperty(“price”, 2.99) method 2. The setProperty() method updates the value of the backingData.price property and calls the notify() method 3. The notify() method executes each function in the collection of listeners associated with the price property Creating Observable Listeners If you want to be notified when a property of an observable object is changed, then you need to register a listener. You register a listener by using the bind() method like this: (function () { "use strict"; var app = WinJS.Application; app.onactivated = function (eventObject) { if (eventObject.detail.kind === Windows.ApplicationModel.Activation.ActivationKind.launch) { // Simple product object var product = { name: "Milk", description: "Something to drink", price: 12.33 }; // Create observable product var observableProduct = WinJS.Binding.as(product); // Execute a function when price is changed observableProduct.bind("price", function (newValue) { console.log(newValue); }); // Change the price observableProduct.price = 2.99; } }; app.start(); })(); In the code above, the bind() method is used to associate the price property with a function. When the price property is changed, the function logs the new value of the price property to the Visual Studio JavaScript console. The price property is associated with the function using the following line of code: // Execute a function when price is changed observableProduct.bind("price", function (newValue) { console.log(newValue); }); Coalescing Notifications If you make multiple changes to a property – one change immediately following another – then separate notifications won’t be sent. Instead, any listeners are notified only once. The notifications are coalesced into a single notification. For example, in the following code, the product price property is updated three times. However, only one message is written to the JavaScript console. Only the last value assigned to the price property is written to the JavaScript Console window: // Simple product object var product = { name: "Milk", description: "Something to drink", price: 12.33 }; // Create observable product var observableProduct = WinJS.Binding.as(product); // Execute a function when price is changed observableProduct.bind("price", function (newValue) { console.log(newValue); }); // Change the price observableProduct.price = 3.99; observableProduct.price = 2.99; observableProduct.price = 1.99; Only the last value assigned to price, the value 1.99, appears in the console: If there is a time delay between changes to a property then changes result in different notifications. For example, the following code updates the price property every second: // Simple product object var product = { name: "Milk", description: "Something to drink", price: 12.33 }; // Create observable product var observableProduct = WinJS.Binding.as(product); // Execute a function when price is changed observableProduct.bind("price", function (newValue) { console.log(newValue); }); // Add 1 to price every second window.setInterval(function () { observableProduct.price += 1; }, 1000); In this case, separate notification messages are logged to the JavaScript Console window: If you need to prevent multiple notifications from being coalesced into one then you can take advantage of promises. I discussed WinJS promises in a previous blog entry: http://stephenwalther.com/blog/archive/2012/02/22/windows-web-applications-promises.aspx Because the updateProperty() method returns a promise, you can create different notifications for each change in a property by using the following code: // Change the price observableProduct.updateProperty("price", 3.99) .then(function () { observableProduct.updateProperty("price", 2.99) .then(function () { observableProduct.updateProperty("price", 1.99); }); }); In this case, even though the price is immediately changed from 3.99 to 2.99 to 1.99, separate notifications for each new value of the price property are sent. Bypassing Notifications Normally, if a property of an observable object has listeners and you change the property then the listeners are notified. However, there are certain situations in which you might want to bypass notification. In other words, you might need to change a property value silently without triggering any functions registered for notification. If you want to change a property without triggering notifications then you should change the property by using the backingData property. The following code illustrates how you can change the price property silently: // Simple product object var product = { name: "Milk", description: "Something to drink", price: 12.33 }; // Create observable product var observableProduct = WinJS.Binding.as(product); // Execute a function when price is changed observableProduct.bind("price", function (newValue) { console.log(newValue); }); // Change the price silently observableProduct.backingData.price = 5.99; console.log(observableProduct.price); // Writes 5.99 The price is changed to the value 5.99 by changing the value of backingData.price. Because the observableProduct.price property is not set directly, any listeners associated with the price property are not notified. When you change the value of a property by using the backingData property, the change in the property happens synchronously. However, when you change the value of an observable property directly, the change is always made asynchronously. Summary The goal of this blog entry was to describe observables. In particular, we discussed how to create observables from existing JavaScript objects and bind functions to observable properties. You also learned how notifications are coalesced (and ways to prevent this coalescing). Finally, we discussed how you can use the backingData property to update an observable property without triggering notifications. In the next blog entry, we’ll see how observables are used with declarative binding to display the values of properties in an HTML document.

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• Knockout with ASP.Net MVC2 - HTML Extension Helpers for input controls

  - by Renso

  Goal: Defining Knockout-style input controls can be tedious and also may be something that you may find obtrusive, mixing your HTML with data bind syntax as well as binding your aspx, ascx files to Knockout. The goal is to make specifying Knockout specific HTML tags easy, seamless really, as well as being able to remove references to Knockout easily. Environment considerations: ASP.Net MVC2 or later Knockoutjs.js How to:     public static class HtmlExtensions     {         public static string DataBoundCheckBox(this HtmlHelper helper, string name, bool isChecked, object htmlAttributes)         {             var builder = new TagBuilder("input");             var dic = new RouteValueDictionary(htmlAttributes) { { "data-bind", String.Format("checked: {0}", name) } };             builder.MergeAttributes(dic);             builder.MergeAttribute("type", @"checkbox");             builder.MergeAttribute("name", name);             builder.MergeAttribute("value", @"true");             if (isChecked)             {                 builder.MergeAttribute("checked", @"checked");             }             return builder.ToString(TagRenderMode.SelfClosing);         }         public static MvcHtmlString DataBoundSelectList(this HtmlHelper helper, string name, IEnumerable<SelectListItem> selectList, String optionLabel)         {             var attrProperties = new StringBuilder();             attrProperties.Append(String.Format("optionsText: '{0}'", name));             if (!String.IsNullOrEmpty(optionLabel)) attrProperties.Append(String.Format(", optionsCaption: '{0}'", optionLabel));             attrProperties.Append(String.Format(", value: {0}", name));             var dic = new RouteValueDictionary { { "data-bind", attrProperties.ToString() } };             return helper.DropDownList(name, selectList, optionLabel, dic);         }         public static MvcHtmlString DataBoundSelectList(this HtmlHelper helper, string name, IEnumerable<SelectListItem> selectList, String optionLabel, object htmlAttributes)         {             var attrProperties = new StringBuilder();             attrProperties.Append(String.Format("optionsText: '{0}'", name));             if (!String.IsNullOrEmpty(optionLabel)) attrProperties.Append(String.Format(", optionsCaption: '{0}'", optionLabel));             attrProperties.Append(String.Format(", value: {0}", name));             var dic = new RouteValueDictionary(htmlAttributes) {{"data-bind", attrProperties}};             return helper.DropDownList(name, selectList, optionLabel, dic);         }         public static String DataBoundSelectList(this HtmlHelper helper, String options, String optionsText, String value)         {             return String.Format("<select data-bind=\"options: {0},optionsText: '{1}',value: {2}\"></select>", options, optionsText, value);         }         public static MvcHtmlString DataBoundTextBox(this HtmlHelper helper, string name, object value, object htmlAttributes)         {             var dic = new RouteValueDictionary(htmlAttributes);             dic.Add("data-bind", String.Format("value: {0}", name));             return helper.TextBox(name, value, dic);         }         public static MvcHtmlString DataBoundTextBox(this HtmlHelper helper, string name, string observable, object value, object htmlAttributes)         {             var dic = new RouteValueDictionary(htmlAttributes);             dic.Add("data-bind", String.Format("value: {0}", observable));             return helper.TextBox(name, value, dic);         }         public static MvcHtmlString DataBoundTextArea(this HtmlHelper helper, string name, string value, int rows, int columns, object htmlAttributes)         {             var dic = new RouteValueDictionary(htmlAttributes);             dic.Add("data-bind", String.Format("value: {0}", name));             return helper.TextArea(name, value, rows, columns, dic);         }         public static MvcHtmlString DataBoundTextArea(this HtmlHelper helper, string name, string observable, string value, int rows, int columns, object htmlAttributes)         {             var dic = new RouteValueDictionary(htmlAttributes);             dic.Add("data-bind", String.Format("value: {0}", observable));             return helper.TextArea(name, value, rows, columns, dic);         }         public static string BuildUrlFromExpression<T>(this HtmlHelper helper, Expression<Action<T>> action)         {             var values = CreateRouteValuesFromExpression(action);             var virtualPath = helper.RouteCollection.GetVirtualPath(helper.ViewContext.RequestContext, values);             if (virtualPath != null)             {                 return virtualPath.VirtualPath;             }             return null;         }         public static string ActionLink<T>(this HtmlHelper helper, Expression<Action<T>> action, string linkText)         {             return helper.ActionLink(action, linkText, null);         }         public static string ActionLink<T>(this HtmlHelper helper, Expression<Action<T>> action, string linkText, object htmlAttributes)         {             var values = CreateRouteValuesFromExpression(action);             var controllerName = (string)values["controller"];             var actionName = (string)values["action"];             values.Remove("controller");             values.Remove("action");             return helper.ActionLink(linkText, actionName, controllerName, values, new RouteValueDictionary(htmlAttributes)).ToHtmlString();         }         public static MvcForm Form<T>(this HtmlHelper helper, Expression<Action<T>> action)         {             return helper.Form(action, FormMethod.Post);         }         public static MvcForm Form<T>(this HtmlHelper helper, Expression<Action<T>> action, FormMethod method)         {             var values = CreateRouteValuesFromExpression(action);             string controllerName = (string)values["controller"];             string actionName = (string)values["action"];             values.Remove("controller");             values.Remove("action");             return helper.BeginForm(actionName, controllerName, values, method);         }         public static MvcForm Form<T>(this HtmlHelper helper, Expression<Action<T>> action, FormMethod method, object htmlAttributes)         {             var values = CreateRouteValuesFromExpression(action);             string controllerName = (string)values["controller"];             string actionName = (string)values["action"];             values.Remove("controller");             values.Remove("action");             return helper.BeginForm(actionName, controllerName, values, method, new RouteValueDictionary(htmlAttributes));         }         public static string VertCheckBox(this HtmlHelper helper, string name, bool isChecked)         {             return helper.CustomCheckBox(name, isChecked, null);         }          public static string CustomCheckBox(this HtmlHelper helper, string name, bool isChecked, object htmlAttributes)         {             TagBuilder builder = new TagBuilder("input");             builder.MergeAttributes(new RouteValueDictionary(htmlAttributes));             builder.MergeAttribute("type", "checkbox");             builder.MergeAttribute("name", name);             builder.MergeAttribute("value", "true");             if (isChecked)             {                 builder.MergeAttribute("checked", "checked");             }             return builder.ToString(TagRenderMode.SelfClosing);         }         public static string Script(this HtmlHelper helper, string script, object scriptAttributes)         {             var pathForCRMScripts = ScriptsController.GetPathForCRMScripts();             if (ScriptOptimizerConfig.EnableMinimizedFileLoad)             {                 string newPathForCRM = pathForCRMScripts + "Min/";                 ScriptsController.ServerPathMapper = new ServerPathMapper();                 string fullPath = ScriptsController.ServerMapPath(newPathForCRM);                 if (!File.Exists(fullPath + script))                     return null;                 if (!Directory.Exists(fullPath))                     return null;                 pathForCRMScripts = newPathForCRM;             }             var builder = new TagBuilder("script");             builder.MergeAttributes(new RouteValueDictionary(scriptAttributes));             builder.MergeAttribute("type", @"text/javascript");             builder.MergeAttribute("src", String.Format("{0}{1}", pathForCRMScripts.Replace("~", String.Empty), script));             return builder.ToString(TagRenderMode.SelfClosing);         }         private static RouteValueDictionary CreateRouteValuesFromExpression<T>(Expression<Action<T>> action)         {             if (action == null)                 throw new InvalidOperationException("Action must be provided");             var body = action.Body as MethodCallExpression;             if (body == null)             {                 throw new InvalidOperationException("Expression must be a method call");             }             if (body.Object != action.Parameters[0])             {                 throw new InvalidOperationException("Method call must target lambda argument");             }             // This will build up a RouteValueDictionary containing the controller name, action name, and any             // parameters passed as part of the "action" parameter.             string name = body.Method.Name;             string controllerName = typeof(T).Name;             if (controllerName.EndsWith("Controller", StringComparison.OrdinalIgnoreCase))             {                 controllerName = controllerName.Remove(controllerName.Length - 10, 10);             }             var values = BuildParameterValuesFromExpression(body) ?? new RouteValueDictionary();             values.Add("controller", controllerName);             values.Add("action", name);             return values;         }         private static RouteValueDictionary BuildParameterValuesFromExpression(MethodCallExpression call)         {             // Build up a RouteValueDictionary containing parameter names as keys and parameter values             // as values based on the MethodCallExpression passed in.             var values = new RouteValueDictionary();             ParameterInfo[] parameters = call.Method.GetParameters();             // If the passed in method has no parameters, just return an empty dictionary.             if (parameters.Length == 0)             {                 return values;             }             for (int i = 0; i < parameters.Length; i++)             {                 object parameterValue;                 Expression expression = call.Arguments[i];                 // If the current parameter is a constant, just use its value as the parameter value.                 var constant = expression as ConstantExpression;                 if (constant != null)                 {                     parameterValue = constant.Value;                 }                 else                 {                     // Otherwise, compile and execute the expression and use that as the parameter value.                     var function = Expression.Lambda<Func<object>>(Expression.Convert(expression, typeof(object)),                                                                    new ParameterExpression[0]);                     try                     {                         parameterValue = function.Compile()();                     }                     catch                     {                         parameterValue = null;                     }                 }                 values.Add(parameters[i].Name, parameterValue);             }             return values;         }     }   Some observations: The first two DataBoundSelectList overloaded methods are specifically built to load the data right into the drop down box as part of the HTML response stream rather than let Knockout's engine populate the options client-side. The third overloaded method does it client-side via the viewmodel. The first two overloads can be done when you have no requirement to add complex JSON objects to your lists. Furthermore, why render and parse the JSON object when you can have it all built and rendered server-side like any other list control.

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• Using Durandal to Create Single Page Apps

  - by Stephen.Walther

  A few days ago, I gave a talk on building Single Page Apps on the Microsoft Stack. In that talk, I recommended that people use Knockout, Sammy, and RequireJS to build their presentation layer and use the ASP.NET Web API to expose data from their server. After I gave the talk, several people contacted me and suggested that I investigate a new open-source JavaScript library named Durandal. Durandal stitches together Knockout, Sammy, and RequireJS to make it easier to use these technologies together. In this blog entry, I want to provide a brief walkthrough of using Durandal to create a simple Single Page App. I am going to demonstrate how you can create a simple Movies App which contains (virtual) pages for viewing a list of movies, adding new movies, and viewing movie details. The goal of this blog entry is to give you a sense of what it is like to build apps with Durandal. Installing Durandal First things first. How do you get Durandal? The GitHub project for Durandal is located here: https://github.com/BlueSpire/Durandal The Wiki — located at the GitHub project — contains all of the current documentation for Durandal. Currently, the documentation is a little sparse, but it is enough to get you started. Instead of downloading the Durandal source from GitHub, a better option for getting started with Durandal is to install one of the Durandal NuGet packages. I built the Movies App described in this blog entry by first creating a new ASP.NET MVC 4 Web Application with the Basic Template. Next, I executed the following command from the Package Manager Console: Install-Package Durandal.StarterKit As you can see from the screenshot of the Package Manager Console above, the Durandal Starter Kit package has several dependencies including: · jQuery · Knockout · Sammy · Twitter Bootstrap The Durandal Starter Kit package includes a sample Durandal application. You can get to the Starter Kit app by navigating to the Durandal controller. Unfortunately, when I first tried to run the Starter Kit app, I got an error because the Starter Kit is hard-coded to use a particular version of jQuery which is already out of date. You can fix this issue by modifying the App_Start\DurandalBundleConfig.cs file so it is jQuery version agnostic like this: bundles.Add( new ScriptBundle("~/scripts/vendor") .Include("~/Scripts/jquery-{version}.js") .Include("~/Scripts/knockout-{version}.js") .Include("~/Scripts/sammy-{version}.js") // .Include("~/Scripts/jquery-1.9.0.min.js") // .Include("~/Scripts/knockout-2.2.1.js") // .Include("~/Scripts/sammy-0.7.4.min.js") .Include("~/Scripts/bootstrap.min.js") ); The recommendation is that you create a Durandal app in a folder off your project root named App. The App folder in the Starter Kit contains the following subfolders and files: · durandal – This folder contains the actual durandal JavaScript library. · viewmodels – This folder contains all of your application’s view models. · views – This folder contains all of your application’s views. · main.js — This file contains all of the JavaScript startup code for your app including the client-side routing configuration. · main-built.js – This file contains an optimized version of your application. You need to build this file by using the RequireJS optimizer (unfortunately, before you can run the optimizer, you must first install NodeJS). For the purpose of this blog entry, I wanted to start from scratch when building the Movies app, so I deleted all of these files and folders except for the durandal folder which contains the durandal library. Creating the ASP.NET MVC Controller and View A Durandal app is built using a single server-side ASP.NET MVC controller and ASP.NET MVC view. A Durandal app is a Single Page App. When you navigate between pages, you are not navigating to new pages on the server. Instead, you are loading new virtual pages into the one-and-only-one server-side view. For the Movies app, I created the following ASP.NET MVC Home controller: public class HomeController : Controller { public ActionResult Index() { return View(); } } There is nothing special about the Home controller – it is as basic as it gets. Next, I created the following server-side ASP.NET view. This is the one-and-only server-side view used by the Movies app: @{ Layout = null; } <!DOCTYPE html> <html> <head> <title>Index</title> </head> <body> <div id="applicationHost"> Loading app.... </div> @Scripts.Render("~/scripts/vendor") <script type="text/javascript" src="~/App/durandal/amd/require.js" data-main="/App/main"></script> </body> </html> Notice that I set the Layout property for the view to the value null. If you neglect to do this, then the default ASP.NET MVC layout will be applied to the view and you will get the <!DOCTYPE> and opening and closing <html> tags twice. Next, notice that the view contains a DIV element with the Id applicationHost. This marks the area where virtual pages are loaded. When you navigate from page to page in a Durandal app, HTML page fragments are retrieved from the server and stuck in the applicationHost DIV element. Inside the applicationHost element, you can place any content which you want to display when a Durandal app is starting up. For example, you can create a fancy splash screen. I opted for simply displaying the text “Loading app…”: Next, notice the view above includes a call to the Scripts.Render() helper. This helper renders out all of the JavaScript files required by the Durandal library such as jQuery and Knockout. Remember to fix the App_Start\DurandalBundleConfig.cs as described above or Durandal will attempt to load an old version of jQuery and throw a JavaScript exception and stop working. Your application JavaScript code is not included in the scripts rendered by the Scripts.Render helper. Your application code is loaded dynamically by RequireJS with the help of the following SCRIPT element located at the bottom of the view: <script type="text/javascript" src="~/App/durandal/amd/require.js" data-main="/App/main"></script> The data-main attribute on the SCRIPT element causes RequireJS to load your /app/main.js JavaScript file to kick-off your Durandal app. Creating the Durandal Main.js File The Durandal Main.js JavaScript file, located in your App folder, contains all of the code required to configure the behavior of Durandal. Here’s what the Main.js file looks like in the case of the Movies app: require.config({ paths: { 'text': 'durandal/amd/text' } }); define(function (require) { var app = require('durandal/app'), viewLocator = require('durandal/viewLocator'), system = require('durandal/system'), router = require('durandal/plugins/router'); //>>excludeStart("build", true); system.debug(true); //>>excludeEnd("build"); app.start().then(function () { //Replace 'viewmodels' in the moduleId with 'views' to locate the view. //Look for partial views in a 'views' folder in the root. viewLocator.useConvention(); //configure routing router.useConvention(); router.mapNav("movies/show"); router.mapNav("movies/add"); router.mapNav("movies/details/:id"); app.adaptToDevice(); //Show the app by setting the root view model for our application with a transition. app.setRoot('viewmodels/shell', 'entrance'); }); }); There are three important things to notice about the main.js file above. First, notice that it contains a section which enables debugging which looks like this: //>>excludeStart(“build”, true); system.debug(true); //>>excludeEnd(“build”); This code enables debugging for your Durandal app which is very useful when things go wrong. When you call system.debug(true), Durandal writes out debugging information to your browser JavaScript console. For example, you can use the debugging information to diagnose issues with your client-side routes: (The funny looking //> symbols around the system.debug() call are RequireJS optimizer pragmas). The main.js file is also the place where you configure your client-side routes. In the case of the Movies app, the main.js file is used to configure routes for three page: the movies show, add, and details pages. //configure routing router.useConvention(); router.mapNav("movies/show"); router.mapNav("movies/add"); router.mapNav("movies/details/:id");   The route for movie details includes a route parameter named id. Later, we will use the id parameter to lookup and display the details for the right movie. Finally, the main.js file above contains the following line of code: //Show the app by setting the root view model for our application with a transition. app.setRoot('viewmodels/shell', 'entrance'); This line of code causes Durandal to load up a JavaScript file named shell.js and an HTML fragment named shell.html. I’ll discuss the shell in the next section. Creating the Durandal Shell You can think of the Durandal shell as the layout or master page for a Durandal app. The shell is where you put all of the content which you want to remain constant as a user navigates from virtual page to virtual page. For example, the shell is a great place to put your website logo and navigation links. The Durandal shell is composed from two parts: a JavaScript file and an HTML file. Here’s what the HTML file looks like for the Movies app: <h1>Movies App</h1> <div class="container-fluid page-host"> <!--ko compose: { model: router.activeItem, //wiring the router afterCompose: router.afterCompose, //wiring the router transition:'entrance', //use the 'entrance' transition when switching views cacheViews:true //telling composition to keep views in the dom, and reuse them (only a good idea with singleton view models) }--><!--/ko--> </div> And here is what the JavaScript file looks like: define(function (require) { var router = require('durandal/plugins/router'); return { router: router, activate: function () { return router.activate('movies/show'); } }; }); The JavaScript file contains the view model for the shell. This view model returns the Durandal router so you can access the list of configured routes from your shell. Notice that the JavaScript file includes a function named activate(). This function loads the movies/show page as the first page in the Movies app. If you want to create a different default Durandal page, then pass the name of a different age to the router.activate() method. Creating the Movies Show Page Durandal pages are created out of a view model and a view. The view model contains all of the data and view logic required for the view. The view contains all of the HTML markup for rendering the view model. Let’s start with the movies show page. The movies show page displays a list of movies. The view model for the show page looks like this: define(function (require) { var moviesRepository = require("repositories/moviesRepository"); return { movies: ko.observable(), activate: function() { this.movies(moviesRepository.listMovies()); } }; }); You create a view model by defining a new RequireJS module (see http://requirejs.org). You create a RequireJS module by placing all of your JavaScript code into an anonymous function passed to the RequireJS define() method. A RequireJS module has two parts. You retrieve all of the modules which your module requires at the top of your module. The code above depends on another RequireJS module named repositories/moviesRepository. Next, you return the implementation of your module. The code above returns a JavaScript object which contains a property named movies and a method named activate. The activate() method is a magic method which Durandal calls whenever it activates your view model. Your view model is activated whenever you navigate to a page which uses it. In the code above, the activate() method is used to get the list of movies from the movies repository and assign the list to the view model movies property. The HTML for the movies show page looks like this: <table> <thead> <tr> <th>Title</th><th>Director</th> </tr> </thead> <tbody data-bind="foreach:movies"> <tr> <td data-bind="text:title"></td> <td data-bind="text:director"></td> <td><a data-bind="attr:{href:'#/movies/details/'+id}">Details</a></td> </tr> </tbody> </table> <a href="#/movies/add">Add Movie</a> Notice that this is an HTML fragment. This fragment will be stuffed into the page-host DIV element in the shell.html file which is stuffed, in turn, into the applicationHost DIV element in the server-side MVC view. The HTML markup above contains data-bind attributes used by Knockout to display the list of movies (To learn more about Knockout, visit http://knockoutjs.com). The list of movies from the view model is displayed in an HTML table. Notice that the page includes a link to a page for adding a new movie. The link uses the following URL which starts with a hash: #/movies/add. Because the link starts with a hash, clicking the link does not cause a request back to the server. Instead, you navigate to the movies/add page virtually. Creating the Movies Add Page The movies add page also consists of a view model and view. The add page enables you to add a new movie to the movie database. Here’s the view model for the add page: define(function (require) { var app = require('durandal/app'); var router = require('durandal/plugins/router'); var moviesRepository = require("repositories/moviesRepository"); return { movieToAdd: { title: ko.observable(), director: ko.observable() }, activate: function () { this.movieToAdd.title(""); this.movieToAdd.director(""); this._movieAdded = false; }, canDeactivate: function () { if (this._movieAdded == false) { return app.showMessage('Are you sure you want to leave this page?', 'Navigate', ['Yes', 'No']); } else { return true; } }, addMovie: function () { // Add movie to db moviesRepository.addMovie(ko.toJS(this.movieToAdd)); // flag new movie this._movieAdded = true; // return to list of movies router.navigateTo("#/movies/show"); } }; }); The view model contains one property named movieToAdd which is bound to the add movie form. The view model also has the following three methods: 1. activate() – This method is called by Durandal when you navigate to the add movie page. The activate() method resets the add movie form by clearing out the movie title and director properties. 2. canDeactivate() – This method is called by Durandal when you attempt to navigate away from the add movie page. If you return false then navigation is cancelled. 3. addMovie() – This method executes when the add movie form is submitted. This code adds the new movie to the movie repository. I really like the Durandal canDeactivate() method. In the code above, I use the canDeactivate() method to show a warning to a user if they navigate away from the add movie page – either by clicking the Cancel button or by hitting the browser back button – before submitting the add movie form: The view for the add movie page looks like this: <form data-bind="submit:addMovie"> <fieldset> <legend>Add Movie</legend> <div> <label> Title: <input data-bind="value:movieToAdd.title" required /> </label> </div> <div> <label> Director: <input data-bind="value:movieToAdd.director" required /> </label> </div> <div> <input type="submit" value="Add" /> <a href="#/movies/show">Cancel</a> </div> </fieldset> </form> I am using Knockout to bind the movieToAdd property from the view model to the INPUT elements of the HTML form. Notice that the FORM element includes a data-bind attribute which invokes the addMovie() method from the view model when the HTML form is submitted. Creating the Movies Details Page You navigate to the movies details Page by clicking the Details link which appears next to each movie in the movies show page: The Details links pass the movie ids to the details page: #/movies/details/0 #/movies/details/1 #/movies/details/2 Here’s what the view model for the movies details page looks like: define(function (require) { var router = require('durandal/plugins/router'); var moviesRepository = require("repositories/moviesRepository"); return { movieToShow: { title: ko.observable(), director: ko.observable() }, activate: function (context) { // Grab movie from repository var movie = moviesRepository.getMovie(context.id); // Add to view model this.movieToShow.title(movie.title); this.movieToShow.director(movie.director); } }; }); Notice that the view model activate() method accepts a parameter named context. You can take advantage of the context parameter to retrieve route parameters such as the movie Id. In the code above, the context.id property is used to retrieve the correct movie from the movie repository and the movie is assigned to a property named movieToShow exposed by the view model. The movie details view displays the movieToShow property by taking advantage of Knockout bindings: <div> <h2 data-bind="text:movieToShow.title"></h2> directed by <span data-bind="text:movieToShow.director"></span> </div> Summary The goal of this blog entry was to walkthrough building a simple Single Page App using Durandal and to get a feel for what it is like to use this library. I really like how Durandal stitches together Knockout, Sammy, and RequireJS and establishes patterns for using these libraries to build Single Page Apps. Having a standard pattern which developers on a team can use to build new pages is super valuable. Once you get the hang of it, using Durandal to create new virtual pages is dead simple. Just define a new route, view model, and view and you are done. I also appreciate the fact that Durandal did not attempt to re-invent the wheel and that Durandal leverages existing JavaScript libraries such as Knockout, RequireJS, and Sammy. These existing libraries are powerful libraries and I have already invested a considerable amount of time in learning how to use them. Durandal makes it easier to use these libraries together without losing any of their power. Durandal has some additional interesting features which I have not had a chance to play with yet. For example, you can use the RequireJS optimizer to combine and minify all of a Durandal app’s code. Also, Durandal supports a way to create custom widgets (client-side controls) by composing widgets from a controller and view. You can download the code for the Movies app by clicking the following link (this is a Visual Studio 2012 project): Durandal Movie App

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