The Hero Editor

2.2

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Every story starts somewhere. Our story starts where the starter app ends.

First, we'll modify the app to display information about a hero. Then we'll start adding the ability to edit the hero's data.

Run the for this part.

Showing our hero

We want to display hero data in our app.

Let's add two properties to our AppComponent, a title property for the application name and a hero property for a hero named "Windstorm".

app_component.dart (AppComponent class)

class AppComponent { String title = 'Tour of Heroes'; var hero = 'Windstorm'; }

Now we update the template in the @Component annotation with data bindings to these new properties.

template: '<h1>{{title}}</h1><h2>{{hero}} details!</h2>'

The browser should refresh and display our title and hero.

The double curly braces tell our app to read the title and hero properties from the component and render them. This is the "interpolation" form of one-way data binding.

Learn more about interpolation in the Displaying Data page.

Hero object

At the moment, our hero is just a name. Our hero needs more properties. Let's convert the hero from a literal string to a class.

Create a Hero class with id and name properties. Keep this near the top of the app_component.dart file for now.

app_component.dart (Hero class)

class Hero { final int id; String name; Hero(this.id, this.name); }

Now that we have a Hero class, let’s refactor our component’s hero property to be of type Hero. Then initialize it with an id of 1 and the name, "Windstorm".

app_component.dart (hero property)

Hero hero = new Hero(1, 'Windstorm');

Because we changed the hero from a string to an object, we update the binding in the template to refer to the hero’s name property.

template: '<h1>{{title}}</h1><h2>{{hero.name}} details!</h2>'

The browser refreshes and continues to display our hero’s name.

Adding more HTML

Displaying a name is good, but we want to see all of our hero’s properties. We’ll add a <div> for our hero’s id property and another <div> for our hero’s name.

template: '<h1>{{title}}</h1><h2>{{hero.name}} details!</h2><div><label>id: </label>{{hero.id}}</div><div><label>name: </label>{{hero.name}}</div>'

Uh oh, our template string is getting long. We better take care of that to avoid the risk of making a typo in the template.

Multi-line template strings

We could make a more readable template with string concatenation but that gets ugly fast, it is harder to read, and it is easy to make a spelling error. Instead, let’s take advantage of the template strings feature in Dart to maintain our sanity.

Change the quotes around the template to triple quotes and put the <h1>, <h2> and <div> elements on their own lines.

app_component.dart (AppComponent's template)

template: ''' <h1>{{title}}</h1> <h2>{{hero.name}} details!</h2> <div><label>id: </label>{{hero.id}}</div> <div><label>name: </label>{{hero.name}}</div>'''

Editing our hero

We want to be able to edit the hero name in a textbox.

Refactor the hero name <label> with <label> and <input> elements as shown below:

app_component.dart (input element)

template: ''' <h1>{{title}}</h1> <h2>{{hero.name}} details!</h2> <div><label>id: </label>{{hero.id}}</div> <div> <label>name: </label> <input value="{{hero.name}}" placeholder="name"> </div>'''

We see in the browser that the hero’s name does appear in the <input> textbox. But something doesn’t feel right. When we change the name, we notice that our change is not reflected in the <h2>. We won't get the desired behavior with a one-way binding to <input>.

Two-way binding

We intend to display the name of the hero in the <input>, change it, and see those changes wherever we bind to the hero’s name. In short, we want two-way data binding.

Let’s update the template to use the ngModel built-in directive for two-way binding.

Learn more about ngModel in the Forms and Template Syntax pages.

Replace the <input> with the following HTML

<input [(ngModel)]="hero.name" placeholder="name">

The browser refreshes. We see our hero again. We can edit the hero’s name and see the changes reflected immediately in the <h2>.

Recap

Let’s take stock of what we’ve built.

  • Our Tour of Heroes uses the double curly braces of interpolation (a form of one-way data binding) to display the application title and properties of a Hero object.
  • We wrote a multi-line template using Dart's template strings to make our template readable.
  • We can both display and change the hero’s name after adding a two-way data binding to the <input> element using the built-in ngModel directive.
  • The ngModel directive also propagates changes to every other binding of the hero.name.

Here's the complete app_component.dart as it stands now:

app_component.dart

import 'package:angular2/core.dart'; class Hero { final int id; String name; Hero(this.id, this.name); } @Component( selector: 'my-app', template: ''' <h1>{{title}}</h1> <h2>{{hero.name}} details!</h2> <div><label>id: </label>{{hero.id}}</div> <div> <label>name: </label> <input [(ngModel)]="hero.name" placeholder="name"> </div>''' ) class AppComponent { String title = 'Tour of Heroes'; Hero hero = new Hero(1, 'Windstorm'); }

What's next

Our Tour of Heroes only displays one hero and we really want to display a list of heroes. We also want to allow the user to select a hero and display their details. We’ll learn more about how to retrieve lists, bind them to the template, and allow a user to select it in the next tutorial page.