Heavily drawing inspiration from Ruby on Rails, MVC4’s convention over configuration model of development soon became
the Holy Grail of .NET web development.
The MVC model brought with it
the goodness of proper separation of concerns between business logic, data, and
the presentation logic.
However,
the MVC paradigm, was still one in which server side .NET code could be mixed with presentation code.
The Razor templating engine, though cleaner than its predecessors, still encouraged and allowed you
to mix .NET server side code with presentation logic. Thus, for example, if
the developer required a certain <div> tag
to be shown if a particular variable ShowDiv was true in
the View’s model,
the code could look like
the following:
Fig 1:
To show a div or not. Server side .NET code is used in
the View
Mixing .NET code with HTML in views can soon get very messy. Wouldn’t it be nice if
the presentation layer (HTML) could be pure HTML? Also, in
the ASP.NET MVC model, some of
the business logic invariably resides in
the controller. It is tempting
to use an antipattern like
the one shown above
to control whether a div should be shown or not.
However, best practice would indicate that
the Controller should not be aware of
the div.
The ShowDiv variable in
the model should not exist. A controller should ideally, only be used
to do
the plumbing of getting
the data populated in
the model and nothing else.
The view (ideally pure HTML) should render
the presentation layer based on
the model.
In this article we will see
how Angular JS, a new JavaScript framework by Google can be used effectively
to build web applications where:
1. Views are pure HTML
2. Controllers (in
the server sense) are pure REST based API calls
3.
The presentation layer is loaded as needed from partial HTML only files.
What is MVVM?
MVVM short for Model View View Model is a new paradigm in web development. In this paradigm,
the Model and View stuff exists on
the client side through javascript instead of being processed on
the server through postbacks. These frameworks are JavaScript frameworks that facilitate
the clear separation of
the “frontend” or
the data rendering logic from
the “backend” which is typically just a REST based API that loads and processes data through a resource model.
The frameworks are called MVVM as a
change to the Model (through javascript) gets reflected in
the view immediately i.e. Model > View. Also, a
change on
the view (through manual input) gets reflected in
the model immediately i.e. View > Model.
The following figure shows this conceptually (comments are shown in red):
Fig 2: Demonstration of MVVM in action
In Fig 2, two text boxes are bound
to the same variable model.myInt. Thus, changing
the view manually (changing one text box through keyboard input) also changes
the other textbox in real time demonstrating V > M property of a MVVM framework.
Furthermore, clicking
the button adds 1
to the value of model.myInt thus changing
the model through JavaScript. This immediately updates
the view (the value in
the two textboxes) thus demonstrating
the M > V property of a MVVM framework.
Thus we see that
the model in a MVVM JavaScript framework can be regarded as “the single source of truth“. This is an important concept. Angular is one such MVVM framework. We shall use it
to build a simple app that sends SMS messages
to a particular number.
Application, Routes, Views, Controllers, Scope and Models
Angular can be used in many ways
to construct web applications. For this article, we shall only focus on building Single Page Applications (SPAs). Many of
the approaches we will follow in this article have alternatives. It is beyond
the scope of this article
to explain every nuance in detail but we shall try
to touch upon
the basic concepts and end up with a working application that can be used
to send SMS messages using Sent.ly Plus (a service that is itself built using Angular).
Before you read on, we would like
to urge you
to forget what you know about Models, Views, Controllers and Routes in
the ASP.NET MVC4 framework. All these words have different meanings in
the Angular world. Whenever these words are used in this article, they will refer
to Angular concepts and not ASP.NET MVC4 concepts.
The following figure shows
the skeleton of
the root page of an SPA:
Fig 3:
The skeleton of a SPA
The skeleton of
the application is based on
the Bootstrap starter template which can be found at: http://getbootstrap.com/examples/startertemplate/
Apart from loading
the Angular, jQuery and Bootstrap JavaScript libraries, it also loads our custom scripts
/app/js/controllers.js /app/js/app.js
These scripts define
the routes, views and controllers which we shall come
to in a moment.
Application
Notice that
the body tag (Fig. 3) has an extra attribute:
ngapp=”smsApp”
Providing this tag “bootstraps” our single page application. It tells Angular
to load a “module” called smsApp. This “module” is defined /app/js/app.js
angular.module('smsApp', ['smsApp.controllers', function () {}])
Fig 4:
The definition of our application module
The line shows above, declares a module called smsApp. It also declares that this module “depends” on another module called “smsApp.controllers”.
The smsApp.controllers module will contain all
the controllers for our SPA.
Routing and Views
Notice that in
the Navbar (in Fig 3) we have included two hyperlinks to:
“#/app” “#/help”
This is
how Angular handles routing. Since
the URLs start with “#”, they are actually just bookmarks (and not server side resources). However, our route definition (in /app/js/app.js) gives these URLs a special meaning within
the Angular framework.
angular.module('smsApp', ['smsApp.controllers', function () {
}])
//Configure
the routes
.config(['$routeProvider', function ($routeProvider) {
$routeProvider.when('/binding', {
templateUrl: '/app/partials/bindingexample.html',
controller: 'BindingController'
});
}]);
Fig 5:
The definition of a route with an associated partial view and controller
As we can see from
the previous code sample, we are using
the $routeProvider object in
the configuration of our smsApp module. Notice
how the code “asks for”
the $routeProvider object by specifying it as a dependency in
the [] braces and then defining a function that accepts it as a parameter. This is known as dependency injection. Please refer
to the following link if you want
to delve into this topic: http://docs.angularjs.org/guide/di
What
the above code snippet is doing is that it is telling Angular that when
the URL is “#/binding”, then it should load
the HTML snippet (“partial view”) found at /app/partials/bindingexample.html. Also, for this URL, Angular should load
the controller called “BindingController”.
We have also marked
the div with
the class “container” (in Fig 3) with
the ngview attribute. This attribute tells Angular that views (partial HTML pages) defined in
the routes will be loaded within this div.
You can see that
the Angular JavaScript framework, unlike many other frameworks, works purely by extending HTML tags and attributes. It also allows you
to extend HTML with your own tags and attributes (through directives) if you so desire, you can find out more about directives at
the following URL: http://www.codeproject.com/Articles/607873/ExtendingHTMLwithAngularJSDirectives
Controllers and Models
We have seen
how we define what views and controllers should be loaded for a particular route. Let us now consider
how controllers are defined. Our controllers are defined in
the file /app/js/controllers.js.
The following snippet shows
the definition of
the “BindingController” which is loaded when we hit
the URL http://localhost:port/index.html#/binding (as we have defined in
the route earlier as shown in Fig 5).
Remember that we had defined that our application module “smsApp” depends on
the “smsApp.controllers” module (see Fig 4).
The code snippet below shows
how the “BindingController” defined in
the route shown in Fig 5 is defined in
the module smsApp.controllers:
angular.module('smsApp.controllers', [function () {
}])
.controller('BindingController', ['$scope', function ($scope) {
$scope.model = {};
$scope.model.myInt = 6;
$scope.addOne = function () {
$scope.model.myInt++;
}
}]);
Fig 6:
The definition of a controller in
the “smsApp.controllers” module.
The pieces are falling in place! Remember Fig.2? That was
the code of a partial view that was loaded within
the container div of
the skeleton SPA shown in Fig 3.
The route definition shown in Fig 5 also defined that
the controller called “BindingController” (shown in Fig 6.) was loaded when we loaded
the URL: http://localhost:22544/index.html#/binding
The button in Fig 2 was marked with
the attribute ngclick=”addOne()” which added 1
to the value of model.myInt. In Fig 6, we can see that this function is actually defined in
the “BindingController”.
Scope
We can see from Fig 6, that in
the definition of “BindingController”, we defined a dependency on $scope and then, as usual, defined a function which “asks for” $scope as per
the dependency injection pattern.
So what is $scope? Any guesses? As you might have guessed a scope is a particular “address space” where variables and functions may be defined. This has a similar meaning
to scope in a programming language like C#.
Model:
The Scope is not
the Model
It is tempting
to assign variables in
the scope directly. For example, we could have defined myInt as $scope.myInt = 6 in Fig 6 instead of $scope.model.myInt = 6.
The reason why this is a bad idea is that scope in hierarchical in Angular. Thus if we were
to define a controller which was defined within
the another controller (nested controllers), then
the inner controller would inherit
the scope of
the parent controller. This inheritance would follow JavaScript prototypal inheritance.
Let’s say
the parent controller defined a variable through $scope.myInt = 6.
The child controller would inherit
the scope through java prototypical inheritance. This basically means that
the child scope has a variable myInt that points
to the parent scopes myInt variable. Now if we assigned
the value of myInt in
the parent,
the child scope would be updated with
the same value as
the child scope’s myInt variable points
to the parent scope’s myInt variable.
However, if we were
to assign
the value of
the myInt variable in
the child scope, then
the link of that variable
to the parent scope would be broken as
the variable myInt in
the child scope now points
to the value 6 and not
to the parent scope’s myInt variable.
But, if we defined a variable model in
the parent scope, then
the child scope will also have a variable model that points
to the model variable in
the parent scope. Updating
the value of $scope.model.myInt in
the parent scope would
change the model variable in
the child scope too as
the variable is pointed
to the model variable in
the parent scope.
Now changing
the value of $scope.model.myInt in
the child scope would ALSO
change the value in
the parent scope. This is because
the model reference in
the child scope is pointed
to the scope variable in
the parent. We did no new assignment
to the model variable in
the child scope. We only changed an attribute of
the model variable. Since
the model variable (in
the child scope) points
to the model variable in
the parent scope, we have successfully changed
the value of myInt in
the parent scope. Thus
the value of $scope.model.myInt in
the parent scope becomes
the “single source of truth“.
This is a tricky concept, thus it is considered good practice
to NOT use scope inheritance. More info on prototypal inheritance in Angular can be found in
the “JavaScript Prototypal Inheritance” section at
the following URL: https://github.com/angular/angular.js/wiki/UnderstandingScopes.
Building It: An Angular JS application using a .NET Web API Backend
Now that we have a perspective on
the basic components of an MVVM application built using Angular, let’s build something useful. We will build an application that can be used
to send out SMS messages
to a given phone number.
The following diagram describes
the architecture of
the application we are going
to build:
Fig 7: Broad application architecture
We are going
to add an HTML Partial
to our project. This partial will contain
the form fields that will accept
the phone number and message that needs
to be sent as an SMS. It will also display all
the messages that have previously been sent.
All
the executable code that is run on
the occurrence of events (button clicks etc.) in
the view resides in
the controller.
The controller interacts with
the ASP.NET WebAPI
to get a history of SMS messages, add a message etc. through a REST based API. For
the purposes of simplicity, we will use an in memory data structure for
the purposes of creating this application.
Thus,
the tasks ahead of us are:
Creating
the REST WebApi with GET, PUT, POST, DELETE methods.
Creating
the SmsView.html partial
Creating
the SmsController controller with methods that are called from
the SmsView.html partial
Add a new route that loads
the controller and
the partial.
1. Creating
the REST WebAPI
This is a simple task that should be quite straightforward
to any .NET developer.
The following listing shows our ApiController:
public class SmsMessage
{
public string
to { get; set; }
public string message { get; set; }
}
public class SmsResource : SmsMessage
{
public int smsId { get; set; }
}
public class SmsResourceController : ApiController
{
public static Dictionary<int, SmsResource> messages = new Dictionary<int, SmsResource>();
public static int currentId = 0;
// GET api/<controller>
public List<SmsResource> Get()
{
List<SmsResource> result = new List<SmsResource>();
foreach (int key in messages.Keys)
{
result.Add(messages[key]);
}
return result;
}
// GET api/<controller>/5
public SmsResource Get(int id)
{
if (messages.ContainsKey(id))
return messages[id];
return null;
}
// POST api/<controller>
public List<SmsResource> Post([FromBody] SmsMessage value)
{
//Synchronize on messages so we don't have id collisions
lock (messages)
{
SmsResource res = (SmsResource) value;
res.smsId = currentId++;
messages.Add(res.smsId, res);
//SentlyPlusSmsSender.SendMessage(value.
to, value.message);
return Get();
}
}
// PUT api/<controller>/5
public List<SmsResource> Put(int id, [FromBody] SmsMessage value)
{
//Synchronize on messages so we don't have id collisions
lock (messages)
{
if (messages.ContainsKey(id))
{
//Update
the message
messages[id].message = value.message;
messages[id].
to = value.message;
}
return Get();
}
}
// DELETE api/<controller>/5
public List<SmsResource> Delete(int id)
{
if (messages.ContainsKey(id))
{
messages.Remove(id);
}
return Get();
}
}
Once this class is defined, we should be able
to access
the WebAPI by a simple GET request using
the browser: http://localhost:port/api/SmsResource
Notice
the commented line: //SentlyPlusSmsSender.SendMessage
The SentlyPlusSmsSender class is defined in
the attached solution. We have shown this line as commented as we want
to explain
the core Angular concepts. If you load
the attached solution, this line is uncommented in
the source and an actual SMS will be sent!
By default,
the API returns XML. For consumption of
the API in Angular, we would like it
to return JSON.
To change the default
to JSON, we make
the following
change to WebApiConfig.cs file located in
the App_Start folder.
public static class WebApiConfig
{
public static void Register(HttpConfiguration config)
{
config.Routes.MapHttpRoute(
name: "DefaultApi",
routeTemplate: "api/{controller}/{id}",
defaults: new { id = RouteParameter.Optional }
);
var appXmlType =
config.Formatters.XmlFormatter.
SupportedMediaTypes.
FirstOrDefault(
t => t.MediaType == "application/xml");
config.Formatters.XmlFormatter.SupportedMediaTypes.Remove(appXmlType);
}
}
We now have our backend REST Api which we can consume from Angular!
2. Creating
the SmsView.html partial
This simple partial will define two fields:
the destination phone number (international format starting with a +) and
the message. These fields will be bound
to model.phoneNumber and model.message. We will also add a button that we shall hook up
to sendMessage() in
the controller. A list of all previously sent messages (bound
to model.allMessages) will also be displayed below
the form input.
The following code shows
the code for
the partial:
<!-- If model.errorMessage is defined, then render
the error div ->
<div class="alert alert-danger alert-dismissable" style="margin-top: 30px;"
ng-show="model.errorMessage != undefined">
<button type="button" class="close" datadismiss="alert" ariahidden="true">×</button>
<strong>Error!</strong>
<br />
{{ model.errorMessage }}
</div>
<!--
The input fields bound
to the model -->
<div class="well" style="margin-top: 30px;">
<table style="width: 100%;">
<tr>
<td style="width: 45%; text-align: center;">
<input type="text" placeholder="Phone number (eg; +44 7778 609466)" ng-model="model.phoneNumber" class="form-control" style="width: 90%" onkeypress="return checkPhoneInput();" />
</td>
<td style="width: 45%; text-align: center;">
<input type="text" placeholder="Message" ng-model="model.message" class="form-control" style="width: 90%" />
</td>
<td style="text-align: center;">
<button class="btn btn-danger" ng-click="sendMessage();" ng-disabled="model.isAjaxInProgress" style="marginright: 5px;">Send</button>
<img src="/Content/ajax-loader.gif" ng-show="model.isAjaxInProgress" />
</td>
</tr>
</table>
</div>
<!--
The past messages -->
<div style="margin-top: 30px;">
<!--
The following div is shown if there are no past messages -->
<div ng-show="model.allMessages.length == 0">
No messages have been sent yet!
</div>
<!--
The following div is shown if there are some past messages -->
<div ng-show="model.allMessages.length == 0">
<table style="width: 100%;" class="table table-striped">
<tr>
<td>Phone Number</td>
<td>Message</td>
<td></td>
</tr>
<!--
The ng-repeat directive is line
the repeater control in .NET, but as you can see this partial is pure HTML which is much cleaner -->
<tr ng-repeat="message in model.allMessages">
<td>{{ message.
to }}</td>
<td>{{ message.message }}</td>
<td>
<button class="btn btn-danger" ng-click="delete(message.smsId);" ng-disabled="model.isAjaxInProgress">Delete</button>
</td>
</tr>
</table>
</div>
</div>
The above code is commented and should be self explanatory. Conditional rendering is achieved through using
the ng-show=”condition” attribute on various div tags.
Input fields are bound
to the model and
the send button is bound
to the sendMessage() function in
the controller as through
the ngclick=”sendMessage()” attribute defined on
the button tag.
While AJAX calls are taking place,
the controller sets model.isAjaxInProgress
to true. Based on this variable, buttons are disabled through
the ng-disabled directive which is added as an attribute
to the buttons.
The ng-repeat directive added as an attribute
to the tr tag causes
the table row
to be rendered multiple times much like an ASP.NET repeater.
3. Creating
the SmsController controller
The penultimate piece of our application is
the controller which responds
to events from our view and interacts with our MVC4 REST WebAPI.
The following listing shows
the code we need
to add
to /app/js/controllers.js. Note that controller definitions can be chained. Also note that this controller “asks for”
the $http service.
The $http service is a simple way in Angular
to do AJAX. So far we have only encountered modules, controllers, views and directives in Angular.
The $http is new entity in Angular called a service. More information on Angular services can be found at
the following URL: http://docs.angularjs.org/guide/dev_guide.services.understanding_services.
.controller('SmsController', ['$scope', '$http', function ($scope, $http) {
//We define
the model
$scope.model = {};
//We define
the allMessages array in
the model
//that will contain all
the messages sent so far
$scope.model.allMessages = [];
//The error if any
$scope.model.errorMessage = undefined;
//We initially load data so set
the isAjaxInProgress = true;
$scope.model.isAjaxInProgress = true;
//Load all
the messages
$http({
url: '/api/smsresource', method: "GET"
}).
success(function (data, status, headers, config) {
this callback will be called asynchronously
//when
the response is available
$scope.model.allMessages = data;
//We are done with AJAX loading
$scope.model.isAjaxInProgress = false;
}).
error(function (data, status, headers, config) {
//called asynchronously if an error occurs
//or server returns response with an error status.
$scope.model.errorMessage = "Error occurred status:" + status;
//We are done with AJAX loading
$scope.model.isAjaxInProgress = false;
});
$scope.delete = function (id) {
//We are making an ajax call so we set this
to true
$scope.model.isAjaxInProgress = true;
$http({
url: '/api/smsresource/' + id,
method: "DELETE"
}).
success(function (data, status, headers, config) {
// this callback will be called asynchronously
// when
the response is available
$scope.model.allMessages = data;
//We are done with AJAX loading
$scope.model.isAjaxInProgress = false;
});
error(function (data, status, headers, config) {
// called asynchronously if an error occurs
// or server returns response with an error status.
$scope.model.errorMessage = "Error occurred status:" + status;
//We are done with AJAX loading
$scope.model.isAjaxInProgress = false;
});
}
$scope.sendMessage = function () {
$scope.model.errorMessage = undefined;
var message = '';
if($scope.model.message != undefined)
message = $scope.model.message.trim();
if ($scope.model.phoneNumber == undefined ||
$scope.model.phoneNumber == '' ||
$scope.model.phoneNumber.length < 10 ||
$scope.model.phoneNumber[0] != '+') {
$scope.model.errorMessage = "You must enter a valid phone number in international format. Eg: +44 7778 609466";
return;
}
if (message.length == 0) {
$scope.model.errorMessage = "You must specify a message!";
return;
}
//We are making an ajax call so we set this
to true
$scope.model.isAjaxInProgress = true;
$http({
url: '/api/smsresource', method: "POST",
data: { to: $scope.model.phoneNumber, message: $scope.model.message }
}).
success(function (data, status, headers, config) {
// this callback will be called asynchronously
// when
the response is available
$scope.model.allMessages = data;
//We are done with AJAX loading
$scope.model.isAjaxInProgress = false;
}).
error(function (data, status, headers, config) {
// called asynchronously if an error occurs
// or server returns response with an error status.
$scope.model.errorMessage = "Error occurred status:" + status
// We are done with AJAX loading
$scope.model.isAjaxInProgress = false;
});
}
}]);
We can see from
the previous listing
how the functions that are called from
the view are defined in
the controller. It should also be evident
how easy it is
to make AJAX calls
to consume our MVC4 REST WebAPI. Now we are left with
the final piece. We need
to define a route that associates a particular path with
the view we have defined and
the controller we have defined.
4. Add a new route that loads
the controller and
the partial
This is
the easiest part of
the puzzle. We simply define another route in
the /app/js/app.js file:
$routeProvider.when('/sms', {
templateUrl: '/app/partials/smsview.html',
controller: 'SmsController'
});
Conclusion
In this article we have seen
how much of
the server side functionality in
the MVC4 framework can be moved
to the browser thus delivering a snappy and fast user interface.
We have seen
how we can build client side HTML only views that avoid
the messy syntax offered by server side Razor views.
We have built a functioning app from
the ground up.
The significant advantage of this approach
to building web apps is that
the front end can be completely platform independent. Even though we used ASP.NET
to create our REST API, we could just easily have used any other language such as Node.js, Ruby etc without changing a single line of our front end code.
Angular is a rich framework and we have only touched on basic functionality required
to create a SPA. For readers who wish
to delve further into
the Angular framework, we would recommend
the following URL as a starting point: http://docs.angularjs.org/misc/started.
To get started with
the code for this project:
Sign up for an account at http://plus.sent.ly (free)
Add your phone number
Go
to the “My Identies Page”
Note Down your Sender ID, Consumer Key and Consumer Secret
Download
the code for this article at: https://docs.google.com/file/d/0BzjEWqSE31yoZjZlV0d0R2Y3eW8/edit?usp=sharing
Change the values of Sender Id, Consumer Key and Consumer Secret in
the web.config file
Run
the project through Visual Studio!
