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Archive for AngularJS

May 27, 2016

Angular 2: Filtering a List Using a Computed Property and Setter

Filed under: Angular 2,AngularJS @ 12:34 pm
Tags: ,

In my Pluralsight course: “Angular 2: Getting Started”, I demonstrate how to filter a list using a custom pipe. However, using a custom pipe does not provide easy access to the filtered result. For example, say you also want the count of the filtered list so you can display “5 of 125” or access other information about the list. In these cases, it is best to filter without using a custom pipe. This post shows you one technique: using a computed property and a setter.

Additional techniques for solving this problem are:

This post updates the code available from my github repo. So starting with that code:

1. Change the declarations making the listFilter a private property and adding a productsFiltered computed property. The productsFiltered property will contain the filtered list of products.

pageTitle: string = ‘Product List’;
imageWidth: number = 50;
imageMargin: number = 2;
showImage: boolean = false;
private _listFilter: string;
errorMessage: string;
products: IProduct[];
productsFiltered: IProduct[];

2. Add a property getter and setter for the listFilter property as follows:

get listFilter(): string {
    return this._listFilter;
}

set listFilter(filter: string) {

    this._listFilter = filter;
    filter = filter ? filter.toLocaleLowerCase() : null;
    this.productsFiltered = filter ? this.products.filter((product: IProduct) =>
        product.productName.toLocaleLowerCase().indexOf(filter) !== -1) : this.products;
}

The getter returns the private variable and is used by the template bindings to display the entered filter string. The setter sets the private variable and re-filters the list every time the listFilter property changes.

This is not enough, however. When the page is first displayed the product array is empty. So this code returns an empty collection and nothing appears on the page. We need something to reset this filter when the product data is retrieved.

3. One way to set the listFilter when the data is retrieved is to modify the ngOnInit() method as follows:

ngOnInit(): void {
       this._productService.getProducts()
                 .subscribe(
                   products => this.onProductsRetrieved(products),
                   error =>  this.errorMessage = <any>error);
}

When the products are retrieved, this code calls the onProductsRetrieved method.

4. Create the new onProductsRetrieved method as follows:

onProductsRetrieved(products: IProduct[]) {
    this.products = products;
    this.listFilter = ”;
}

This code sets the retrieved products to our product property and then sets listFilter to an empty string so that our set procedure is executed and our data is displayed.

5. The only other change is to the template:

<tr *ngFor=’let product of productsFiltered‘>

This binds to the productsFiltered property and no longer needs the pipe. We can then also bind other elements to this property or this property’s count method as needed.

Enjoy!

January 26, 2016

Creating a Filter Pipe in Angular 2

Filed under: Angular 2,AngularJS @ 4:23 pm
Tags: ,

Angular 1.x has filters. Angular 2 has pipes, which fulfill a similar purpose. However, there are some key filters in Angular 1.x, such as the “filter filter”, that don’t have an equivalent Angular 2 feature. This post details how to build a filter pipe in Angular 2.

Angular 1.x

In Angular 1.x, we define an input box for a user to enter filter text. We then filter a list of items by that text with one simple clause as shown below:

<div class=”row”>
    <div class=”col-md-2″>Filter by:</div>
    <div class=”col-md-4″><input type=”text” ng-model=”listFilter” /></div>
</div>

<div class=”table-responsive”>
    <table class=”table”>
        <tbody>
            <tr ng-repeat=”movie in vm.movies | filter : {title:listFilter}“>
                <td>{{ movie.title}}</td>
                <td>{{ movie.director }}</td>
                <td>{{ movie.mpaa | uppercase}}</td>
            </tr>
        </tbody>
    </table>
</div>

Easy breezy.

Angular 2

Angular 2 provides pipes for this same purpose. But with no “filter” pipe in Angular 2, we have to build our own pipe component.

Converting the above code into Angular 2 results in:

<div class=”row”>
    <div class=”col-md-2″>Filter by:</div>
    <div class=”col-md-4″><input type=”text” #listFilter (keyup)=”0″ /></div>
</div>

<table class=”table”>
    <tbody>
        <tr *ngFor=”#movie of movies | movieFilter:listFilter.value” >
             <td>{{ movie.title}}</td>
            <td>{{ movie.director }}</td>
            <td>{{ movie.mpaa | uppercase}}</td>
        </tr>
    </tbody>
</table>

Hmmm. That does not look that different!

A few things you’ll notice here:

  • The local variable, listFilter, is now prefixed with a hash symbol (#) to explicitly identify it as a local variable.
    • This variable defines an HTML element, so to obtain the value, we need to access listFilter.value.
  • The (keyup)=”0″ syntax sets up an event listener for the keyup event. There is no event handler needed for this event, so it is just set to “0”.
  • The filter clause is defined here as movieFilter and we are filtering on the value of the listFilter variable. So our custom pipe is used just like the built-in pipes.

The key is creating the movieFilter pipe. In Angular 1.x, the “filter filter” was built in. In Angular 2, there are some built-in filters, but not a general list filter. So we need to build our own.

The purpose of a pipe is to take in a value, filter that value, and return the filtered result. In this example, the value we are taking in is a list of movies. We filter the movies to only those with a title containing the user-entered text. And we return the filtered result.

Here is the code for the movieFilter. The description follows.

import {Pipe, PipeTransform} from ‘angular2/core’;

@Pipe({
    name: ‘movieFilter’
})
export class MovieFilterPipe implements PipeTransform {

    transform(value: any, args: string[]): any {

       let filter = args[0].toLocaleLowerCase();
       return filter ? value.filter(movie=> movie.title.toLocaleLowerCase().indexOf(filter) != -1) : value;
    }
}

1) First we import the Pipe and PipeTransform. This is required to build any pipe.

2) We define a Pipe decorator. This tells Angular that this code is a pipe component. And we give the pipe a name: movieFilter. This is the name used in the HTML as part of a template expression.

3) We create a class that provides the processing for our pipe. We export the class so it can be imported by our movie component. And we implement the PipeTransform interface for our tooling. Note that implementing this interface is optional. With the @Pipe decorator, Angular already expects to find a transform method.

4) The PipeTransform interface requires implementing a transform method. This method has two parameters:

  • value: The value being filtered. In our example, this is the list of movies.
  • args: An optional array of parameters, one for each parameter passed to the pipe. In our example, we are passing listFilter.value.

5) We then define a result array which will contain the movies that match the filter criteria.

6) We create a variable to hold the passed in parameter. We use toLocaleLowerCase() so that the filtering won’t be case sensitive.

7) We check the filter variable. If there is no filter defined, we simply return the original value. No need to iterate the list. Otherwise we use the JavaScript filter function to filter the list and return it.

NOTE: This code could be simplified using regular expressions.

Lastly, we need the component:

import {Component} from ‘angular2/core’;
import {MovieFilterPipe} from ‘../common/movieFilter.pipe’

@Component({
    selector: ‘mh-movie-list’,
    templateUrl: ‘app/movies/movieListView.html’,
    styleUrls: [‘node_modules/bootstrap/dist/css/bootstrap.css’],
    pipes: [MovieFilterPipe]
})
export class MovieListComponent {

}

This is the component associated with the movie list view. The two critical steps for the pipe are:

1) Import the MovieFilterPipe.

2) Identify the pipe using the @Component decorator’s pipes array. This provides the list of all custom pipes available for the template.

For more information on Angular 1.x vs Angular 2, see “Angular 1.x to Angular 2 Quick Reference“.

For a sample application, see “Angular: 3 Flavors” which has the same application in Angular 1.x, Angular 1.x with TypeScript, and Angular 2.

Enjoy!

January 25, 2016

Angular 1 to Angular 2 Quick Reference

Filed under: Angular 2,AngularJS @ 5:04 pm

The post that was here has been edited and re-published here: https://angular.io/docs/ts/latest/cookbook/a1-a2-quick-reference.html.

Enjoy!

September 4, 2015

Use TypeScript to Prepare for Angular 2

If you are developing now in Angular 1.x with an eye toward Angular 2, the best thing you can do is to write your Angular code with TypeScript. Angular 1.x code you write in TypeScript today will look very similar to code you will write in Angular 2 tomorrow (not literally tomorrow!).

At a recent Angular conference, the members of the Angular team from Google stated that one of the best ways to code now in Angular 1.x in preparation for Angular 2 is to use TypeScript.

What is TypeScript?

image

TypeScript is an open-source programming language that is:

  • A superset of JavaScript
    • Including all of the current JavaScript syntax, plus much more.
    • Any valid JavaScript code is valid TypeScript code. And as such, TypeScript works with all existing JavaScript frameworks, including Angular.
  • TypeScript transpiles to plain JavaScript
    • So we can deploy the resulting JavaScript files for our Angular application just as we do now.
    • And the resulting files execute in any of today’s browsers on any OS.
    • Plus there is no runtime overhead of using TypeScript because all of the types evaporate and the TypeScript-only syntax is replaced … leaving only pure JavaScript.
  • TypeScript allows us to define strong types
    • Editor tooling, such as the new Visual Studio Code editor, use these types for static type checking of our code during development
    • This makes development, debugging, and refactoring easier.
    • Plus it clarifies the developer’s intent. For example, we can define that a function is meant to take in a string. Not a number, not an object, just a string.
  • And TypeScript provides class-based object-oriented programming techniques.
    • So we can optionally think of our code in terms of objects with properties and methods.
    • And the TypeScript compiler transpiles the classes into JavaScript functions.

Here is the code for an Angular controller, written using the class-based object-oriented programming techniques available in TypeScript.

AngularWTypeScript_Code

To learn more about using Angular with TypeScript, check out the Pluralsight course: “Angular with TypeScript

AngularWTypeScript

Enjoy!

August 12, 2015

"Angular Front to Back with Web API" Problem Solver

Angular and ASP.NET Web API are like chocolate and peanut butter, they are GREAT together! But there are lots of intricacies and many, many things that can go wrong when putting these two technologies together. This problem solver covers some of the most common things that can go wrong and how to fix them.

The_Creation_Michelangelo

Using Angular as the client technology in the front-end and an ASP.NET Web API service in the back-end is a common requirement. So much so, that I developed a Pluralsight course to help developers tackle all of the touch points between an Angular client application and a back-end ASP.NET Web API service: Angular Front to Back with Web API.

As of this writing, there have been over 400 posts associated with that course, many of which identify problems that developers have had in merging these two technologies. This post summarizes the most common issues and identifies locations in the course where solutions to these issues can be found

 

No Access-Control-Allow-Origin Header is Present

This issue first appears in module 3 (Retrieving Data) clip 6 (Calling the Web API from Angular). We created the ASP.NET Web API code in a project separate from the Angular code. So when the solution is executed:

When the Angular code calls the ASP.NET Web API, it will work in Internet Explorer but *not* in Chrome. In Chrome, pressing the F12 tools will show the error: No “Access-Control-Allow-Origin” header is present, Status Code: 500 Internal Server Error.

This is a problem with cross-origin requests. Since the origin of the call is from http://localhost:52436 and the endpoint is at http://localhost:52293, the request is considered to be a cross-origin request. In other words, the request is originating at a different URL than the service. By default, cross-origin requests are denied. (This works in debug mode with IE because IE does not consider the difference in port numbers to be a cross-origin request.)

The solution to this problem is CORS, or cross-origin resource sharing. Wikipedia states that CORS “allows many resources … on a web page to be requested from another domain outside the domain from which the resource originated.” In other words, CORS defines a way that a service can interact safely with a browser application that originates on a different domain or different server.

To enable CORS in the ASP.NET Web API, start by downloading the CORS package using NuGet Package Manager.

image

Once CORS is installed, there are two additional steps:

1) Call the EnableCors method.

Open the WebApiConfig.cs file in the App_Start folder. Add this line to the Register method:

config.EnableCors();

2) Set the EnableCorsAttribute.

Set this attribute on any controller class that wants to allow cross origin requests. For example, on the ProductsController, it might look like this:

[EnableCorsAttribute(“http://localhost:52436″, “*”, “*”)]
public class ProductsController : ApiController
{}

Note that the port shown in red is the port for the Angular application. This code tells the PrioductsController class that it should allow cross-origin requests only from the defined location, which is from our Angular client application. Alternatively, use “*” to allow access from any cross-origin request.

These steps are covered in detail in module 4 (CORS and Formatters) clip 3 (Enabling CORS in a Web API service).

OData Does Not Work

This issue appears in Module 6 (Using OData Queries) and often takes the form of a problem with the contains method of the OData $filter. This problem is due to confusion on the multiple OData packages that are available in Visual Studio.

The course requires version 4 of OData, so be sure to select the NuGet package that says “OData v4.0” in the description.

NOTE: There are many similarly named NuGet packages, such as “Microsoft.Data.OData” and “Microsoft.AspNet.WebApi.OData”. Be sure to select the one shown below.

image

User Login Generates a CORS Error

This issue appears in module 10 (User Registration and Login). It often only occurs in Chrome (not IE).

There are two possible issues here:

1) There is one line of code that is missing from the demo in the course.

[EnableCorsAttribute(“http://localhost:52436″, “*”, “*”)]
public class AccountController : ApiController
{ }

This line of code enables CORS for the AccountController just as we did for the ProductsController earlier in the course (module 3)

2) There is one line of code added during the demo, but is sometimes missed when coding along.

In the Providers folder, ApplicationOAuthProvider.cs file, GrantResourceOwnerCredentials method, add the following line:

context.OwinContext.Response.Headers.Add(“Access-Control-Allow-Origin”,
    new[] { “
http://localhost:52436″ });

Where the defined URL shown in red is the location of the Angular application that this code is granting access to.

This code is explained and demoed in module 10 (User Registration and Login) clip 4 (Logging the User In) starting around 9:32 with showing the error and the line of code is added at 10:13.

User Registration Network Methods

Several questions have come up regarding the network methods that occur when the Register button is selected to register a new user. I entered a new user name and password, then clicked the Register button. The results are shown below when using Chrome on Windows:

image

Hope this answers the questions.

Save Issues

I have not been able to reproduce any specific issue here … but if you have problems with the Save operation … Try changing this in productResource.js:

‘save’: {
    headers: { ‘Authorization’: ‘Bearer ‘ + currentUser.getProfile().token }
},

With this:

‘save’: {
    method: ‘POST’,
    headers: { ‘Authorization’: ‘Bearer ‘ + currentUser.getProfile().token }
},

Cannot Read Property ‘exceptionMessage’ of Null

This is most likely caused by the exception handling in mainCtrl.js. Change this:

function (response) {
    vm.password = “”;
    vm.message = response.statusText + “\r\n”;
    if (response.data.exceptionMessage)
        vm.message += response.data.exceptionMessage;

    if (response.data.error) {
        vm.message += response.data.error;
    }
});

To this:

function (response) {
    vm.password = “”;
    vm.message = response.statusText + “\r\n”;
    if (response.data && response.data.exceptionMessage)
        vm.message += response.data.exceptionMessage;

    if (response.data && response.data.error) {
        vm.message += response.data.error;
    }
});

Please let me know if you have run into anything else that should be added to this list.

Enjoy!

Angular Custom Services in TypeScript: Factory vs Service

Filed under: AngularJS,TypeScript @ 1:14 pm
Tags: , , ,

In my prior post (http://bit.ly/DeborahK_AngularServices) I outlined the difference between the factory pattern and service pattern when building a custom Angular service with JavaScript. In this post we’ll look at the differences when the Angular custom service is written in TypeScript.

Angular Custom Service

The basic code to create an Angular custom service in TypeScript is the same for both the factor pattern and the service pattern.

Here is an example of a simple custom service written in TypeScript, missing only the Angular module registration:

module app.common {
    export interface IHelloService {
        sayHello(text: string): string;
        sayGoodbye(text: string): string
    }

    export class HelloService implements IHelloService {
        sayHello(text: string): string {
            return “Hello ” + text;
        };
        sayGoodbye(text: string): string {
            return “Goodbye ” + text;
        };
    }
    <Module Registration Here>
}

This code begins with a TypeScript module. The TypeScript module encapsulates the code within an Immediately Invoked Function Expression (IIFE) and provides a clean namespace for the service.

The interface defines the intent of the service. The service intends to provide a sayHello method and a sayGoodbye method. Both take in a string parameter and return a string.

The service class is exported so that it can be used from any other Angular code, such as an Angular controller. The class implements the defined interface, thereby committing to implement every property and method defined in that interface. In our case, it is committing to implement the two methods.

The primary difference between the factory pattern and service pattern when building an Angular service with TypeScript is the module registration. Let’s take a look at how that registration is different.

Service Pattern

When using the service pattern, the TypeScript code to register the service with an Angular module is straightforward.

Simply call the service method:

angular
        .module(“helloWorld”)
        .service(“helloService”,
                         HelloService);

Insert the above code into the service example in place of <Module Registration Here> and you have a working service using the service pattern.

Factory Pattern

Using the factory pattern, the registration code is a little more complex.

As shown in the prior post (http://bit.ly/DeborahK_AngularServices), an Angular factory returns an object. When building the service with a TypeScript class, a class itself cannot return an object. Properties and methods of the class can return an object, but the class itself cannot.

So when using the factory pattern with TypeScript, the trick is to define a function that creates an instance of the service and returns an object. The code for that looks like this:

function factory(): HelloService {
    return new HelloService();
}

angular
    .module(“helloWorld”)
    .factory(“helloService”,
                     factory);

Insert the above code into the service example in place of <Module Registration Here> and you have a working service using the factory pattern.

Enjoy!

For more information on this and many other techniques when building an Angular application with TypeScript, check out my Pluralsight course: “Angular with TypeScript”

AngularWTypeScript2

August 7, 2015

Angular Custom Services: Factory vs Service

Filed under: AngularJS @ 1:11 pm
Tags: , ,

When we want reusable code in our Angular application we build a custom Angular service. We can then use that service in any Angular code that needs it. There are several types of services available in Angular, but there are two types that are used most often: Factory and Service

image

Factory

We can create a service as an Angular factory, also known as a “factory service”.

Here is an example of a simple factory written in JavaScript:

app.factory(‘helloService’, function(){

   return {

      sayHello: function(text){

         return “Hello ” + text;

      },

      sayGoodbye: function(text){

         return “Goodbye ” + text;

      }

   }

});

With a factory-style service we return an object with properties and methods. In this example, the object has two methods: sayHello and sayGoodbye.

This is the recommended and most commonly used type of custom service when coding in JavaScript.

Service

Alternatively, we can create a service as an Angular service, also known as a “service service”.

Here is an example of a simple service written in JavaScript:

app.service(‘helloService’, function(){

   this.sayHello= function(text){

        return “Hello ” + text;

   };

   this.sayGoodbye = function(text){

        return “Goodbye ” + text;

   };

});

With a service-style service, we don’t return anything directly. Rather, we define the service properties and methods on “this”. Those methods may return something, but the service function itself does not.

In many scenarios, it is easier to use a service-style service when coding in TypeScript. In looking at the two different sets of code here, the body of the service code looks more similar to code we would expect to see within a class.

Enjoy!

May 15, 2015

Clearing the Internet Explorer Browser Cache

Filed under: AngularJS @ 10:49 am

When working on an Angular application, it is important to ensure that the browser does not keep prior versions of your JavaScript or other files cached. Otherwise, when you make a change to a JavaScript or HTML file and re-run the application, you may not see your changes.

Here are the steps to ensure that Internet Explorer does not cache your files:

1) Select the Tools icon and select Internet options:

image

2) Click the Settings button (on the General tab)

image

3) Select the desired option. I often pick “Every time I start Internet Explorer”

image

Enjoy!

April 30, 2015

What Developers are Saying About: "Angular Front to Back With Web API"

It is sometimes difficult to find detailed step-by-step guidance for building an application using Angular and ASP.NET Web API. The Pluralsight course: “Angular Front to Back With Web API” covers the following topics from front to back:

  • Retrieving Data
  • CORS and Formatters
  • Passing Parameters
  • Using OData Queries
  • Saving Data
  • Action Results, Error Handling & Validation
  • User Authentication & Authorization

(If you don’t have a Pluralsight membership, sign up for a free trial here.)

Here are some of the comments about the course from Twitter and the course discussion page:

Awesome WebAPI + Angular course!

Thanks for your great course, it helped me to understand how to establish different CURD action between front end and back end.

oh yea! Your course rocks too! Even a beginner can view this course and your other one and be successful.

Great course, it is really concise and to-the-point.

First of all I would like to congratulate you on publishing a fantastic set of courses on AngularJS Line of Business Apps and more so recently Angular Front to Back with Web API. I think what stands out for me is the way in which you provide holistic approach to delivering excellent technical content.

I Love your angularjs pluralsight courses. Learnt a lot and using at work.

Your classes on AngularJS on pluralsight is my reason am better than my peers, thanks

Thank you for building a .Net course F2B that uses (vm = this) and (controller as) syntax!!! You rock.

ScreenShot

Enjoy!

January 12, 2015

What Developers are Saying About: AngularJS Line of Business Applications

Filed under: AngularJS @ 8:56 am
Tags: , ,

Developers interested in building great business applications with AngularJS are finding the Pluralsight course: AngularJS Line of Business Applications to be just what they need.

(If you don’t have a Pluralsight membership, sign up for a free trial here.)

Here are some of the comments in the discussion section for the course:

You’ve built a complete application, which is awesome!

Excellent course. One of the best ones I have ever seen.

Deborah, this is by far the best Angular.js course I’ve seen in the last two years. And believe me, I watch them all. But somehow you’ve managed to explain it so well that I really feel like I can finally make my own applications!

Great course, wish I would of started with it 🙂

Deborah, you speak human language. I loved your style of teaching!

Thanks for the great course! I really appreciated the systematic reinforcement of software engineering best practices that never fell by the wayside, even while building a demo app.

One of the best course on AngularJS at intermediates level. What i liked the most is the pace & clarity on each of the topic covered. I would highly recommend this course.

image

This course covers the following topics:

  • Introduction
  • Building the First Page
  • Accessing Data
  • Routing to Multiple Views
  • Building Data Entry Forms
  • Validating Forms
  • Defining Business Logic in an Angular Service
  • Visualizing Data With Charts
  • Exception Handling
  • Final Words

Enjoy!

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