angular-cn/public/docs/dart/latest/guide/displaying-data.jade

.l-main-section
  p.
      Let's walk through how to display a property and a list of properties,
      and then to conditionally show content
      based on state. The final UI looks like this:

  figure.image-display
    img(src='displaying-data-example1.png')

.l-main-section
  h2#section-create-an-entry-point Create entry points and pubspec

  p.
    Open your favorite editor and create a directory with
    a <code>web/main.dart</code> file,
    a <code>web/index.html</code> file, and
    a <code>pubspec.yaml</code> file:

  .code-box
    pre.prettyprint.lang-dart(data-name="dart")
      code.
        // web/main.dart
        library displaying_data;

        import 'package:angular2/angular2.dart';
        import 'package:angular2/src/reflection/reflection.dart' show reflector;
        import 'package:angular2/src/reflection/reflection_capabilities.dart' show ReflectionCapabilities;

        part 'show_properties.dart';

        main() {
          reflector.reflectionCapabilities = new ReflectionCapabilities();
          bootstrap(DisplayComponent);
        }
    pre.prettyprint.lang-html(data-name="html")
      code.
        &lt;!-- web/index.html --&gt;
        &lt;!DOCTYPE html&gt;
        &lt;html&gt;
          &lt;head&gt;
            &lt;link rel=&quot;stylesheet&quot; href=&quot;style.css&quot;&gt;
          &lt;/head&gt;
          &lt;body&gt;

            &lt;display&gt;&lt;/display&gt;

            &lt;script type=&quot;application/dart&quot; src=&quot;main.dart&quot;&gt;&lt;/script&gt;
            &lt;script src=&quot;packages/browser/dart.js&quot;&gt;&lt;/script&gt;
          &lt;/body&gt;
        &lt;/html&gt;
    pre.prettyprint.lang-yaml(data-name="yaml")
      code.
        # pubspec.yaml
        name: displaying_data
        description: Dart version of Angular 2 example, Displaying Data
        version: 0.0.1
        dependencies:
          angular2: 2.0.0-alpha.21
          browser: any

  p.
   All of this code should look familiar from the previous page,
   except for the <code>library</code> and <code>part</code> statements
   in <code>main.dart</code>.
   Those statements let you implement part of the app in a different Dart file.
   All three of these files remain similar in the rest of the examples,
   so we'll just focus on what's different.

.l-main-section
  h2#section-showing-properties-with-interpolation Showing properties with interpolation
  p.
    The simple method for binding text into templates is through interpolation,
    where you put the name of a property
    inside <strong>{{ }}</strong>.

  p.
    To see this working, create a Dart file under <code>web</code>
    named <code>show_properties.dart</code>,
    and add the following:

  pre.prettyprint.lang-dart
    code.
      // web/show_properties.dart
      part of displaying_data;

      @Component(
        selector: 'display'
      )
      @View(
        template: '''
      &lt;p>My name: {{ myName }}&lt/p>
      '''
      )
      class DisplayComponent {
        String myName = 'Alice';
      }

  p.
    You've just defined a component that encompasses a view and controller for the app. The view
    defines a template:

  pre.prettyprint.lang-html
    code.
      &lt;p&gt;My name: {{ myName }}&lt;/p&gt;

  p.
   Angular will automatically pull the value of <code>myName</code> and
   insert it into the browser,
   automatically updating it whenever it changes.

  .callout.is-helpful
    header Note
    p.
      While you've used <code>template:</code> to specify an inline view, for larger templates you'd
      want to move them to a separate file and load them with <code>templateUrl:</code> instead.

  p.
   One thing to notice is that although you've written
   your <code>DisplayComponent</code> class, you haven't
   used <code>new</code> to instantiate it.
   Because your class is associated with <code>&lt;display&gt;</code> elements in
   the DOM, Angular automatically calls <code>new</code> on
   <code>DisplayComponent</code> and bind its properties to
   that part of the template.

  p.
   When you're building templates, data bindings like these have access to
   the same scope of
   properties as your controller class does.
   Here your class is <code>DisplayComponent</code>, which has
   just one property, <code>myName</code>.

  p.
    Add a second line to the template,
    so you can see Angular dynamically update content:

  pre.prettyprint.lang-html
    code.
      &lt;p&gt;Current time: {{ time }}&lt;/p&gt;

  p.
    Then give the <code>DisplayComponent</code> a starting value for time and
    a call to update time
    via <code>setInterval</code>:

  pre.prettyprint.lang-dart
    code.
      class DisplayComponent {
        String myName = 'Alice';
        String time;
        Timer _timer;

        DisplayComponent() {
          _updateTime(null);
          _timer = new Timer.periodic(new Duration(seconds: 1), _updateTime);
        }

        _updateTime(Timer _) {
          time = new DateTime.now().toString();
        }
      }

  p Reload the app, and you'll now see the seconds updating automatically.

.l-main-section
  h2#Create-an-array Display an iterable using *for
  p Moving up from a single value, create a property that's a list of values.

  pre.prettyprint.lang-dart
    code.
      class DisplayComponent {
        String myName = 'Alice';
        List&lt;String&gt; friendNames = ['Aarav', 'Martín', 'Shannon', 'Ariana', 'Kai'];
      }

  p.
    You can then use this list in your template with the <code>for</code> directive to create copies of DOM elements
    with one for each item in the list.

  pre.prettyprint.lang-dart
    code.
      @View(
        template: '''
      &lt;p>My name: {{ myName }}&lt;/p>
      &lt;p>Friends:&lt;/p>
      &lt;ul>
         &lt;li *for="#name of friendNames">
            {{ name }}
         &lt;/li>
      &lt;/ul>
        '''
        )
  p.
    To make this work, you'll also need to add the Angular <code>For</code> directive used by
    the template to <code>show_properties.dart</code>, so that Angular knows to include it.
    Add <code>For</code> using the optional <code>directives</code> parameter,
    which contains a list of directives:

  pre.prettyprint.lang-dart
    code.
      @View(
        template: '''
      // ...HTML...
        ''',
        directives: const[For]
      )

  p Reload and you've got your list of friends!
  p.
    Again, Angular will mirror changes you make to this list over in the DOM. Add a new item and it appears in your
    list. Delete one and Angular deletes the &lt;li&gt;. Reorder items and Angular makes the corresponding reorder of
    the DOM list.

  p Let's look at the few lines that do the work again:

  pre.prettyprint.lang-html
    code.
      &lt;li *for=&quot;#name of friendNames&quot;&gt;
         {{ name }}
      &lt;/li&gt;

  p The way to read this is:
  ul
    li.
      <code>*for</code>: Create a DOM element for each item in an
      <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols">iterable</a>
       such as a list.
    li <code>#name</code>: Refer to individual values of the iterable as <code>name</code>.
    li <code>of friendNames</code>: The iterable to use is called <code>friendNames</code> in the current controller.

  p Using this syntax, you can build UI lists from any iterable object.

.l-main-section
  h2#Create-a-class Create a model and inject it
  p.
    Before we get too much further, we should mention that putting the model (list) directly into the controller isn't
    proper form.  We should separate the concerns by having another class serve the role of model and inject it into
    the controller.

  p.
    Make a <code>FriendsService</code> class to implement a model containing a list of friends. We'll put this in a new
    <code>friends_service.dart</code> under <code>web/</code>. Here's what the class looks like:

  pre.prettyprint.lang-dart
    code.
      // web/friends_service.dart
      part of displaying_data;

      class FriendsService {
        List&lt;String&gt; friendNames = ['Aarav', 'Martín', 'Shannon', 'Ariana', 'Kai'];
      }

  .callout.is-helpful
    header Note
    p.
      Remember to tie <code>friends_service.dart</code> into the library's main file:
      add <code>part friends_service.dart</code> to <code>main.dart</code>.
  p.
    Now you can replace the current list of friends in DisplayComponent.
    First add a FriendsService parameter to the constructor.
    Then set <code>friendNames</code> to the names provided by the service.

  pre.prettyprint.lang-dart
    code.
      // In web/show_properties.dart
      class DisplayComponent {
        String myName = 'Alice';
        List<String> friendNames;

        DisplayComponent(FriendsService friendsService) {
          friendNames = friendsService.names;
        }
      }

  p.
    Next, make FriendsService available to dependency injection
    by adding an <code>injectables</code> parameter to DisplayComponent's
    <code>@Component</code> annotation:

  pre.prettyprint.lang-dart
      code.
        @Component(
          selector: 'display',
          injectables: const[FriendsService]
        )

.l-main-section
  h2#Conditionally-displaying-data-with-If Conditionally display data using *if
  p.
    Lastly, before we move on, let's handle showing parts of our UI conditionally with <code>*if</code>.  The
    <code>If</code> directive adds or removes elements from the DOM based on the expression you provide.

  p See it in action by adding a paragraph at the end of your template:

  pre.prettyprint.lang-html
    code.
      &lt;p *if=&quot;names.length &gt; 3&quot;&gt;You have many friends!&lt;/p&gt;

  p.
    Also add <code>If</code> to the list of directives,
    so Angular knows to include it:

  pre.prettyprint.lang-dart
    code.
      directives: const[For, If]
  p.
    The list current has 5 items, so if you run the app you'll see the message
    congratulating you on your many friends.
    Remove two items from the list, reload your browser,
    and see that the message no longer displays.
    <!-- PENDING: mention somewhere that once you start a web server,
    you can just refresh the browser to see your changes. -->

  p Here's the final code.

  .code-box
    pre.prettyprint.lang-dart(data-name="show_properties.dart")
      code.
        // web/show_properties.dart
        part of displaying_data;

        @Component(
          selector: 'display',
          injectables: const[FriendsService]
        )
        @View(
          template: '''
        &lt;p>My name: {{ myName }}&lt;/p>
        &lt;p>Friends:&lt;/p>
        &lt;ul>
           &lt;li *for="#name of friendNames">
              {{ name }}
           &lt;/li>
        &lt;/ul>
        ''',
          directives: const[For]
        )
        class DisplayComponent {
          String myName = 'Alice';
          List&lt;String> friendNames;

          DisplayComponent(FriendsService friendsService) {
            friendNames = friendsService.names;
          }
        }
    pre.prettyprint.lang-dart(data-name="friends_service.dart")
      code.
        // web/friends_service.dart
        part of displaying_data;

        class FriendsService {
          List&lt;String> names = ['Aarav', 'Martín', 'Shannon', 'Ariana', 'Kai'];
        }
    pre.prettyprint.lang-dart(data-name="main.dart")
      code.
        // web/main.dart
        library displaying_data;

        import 'dart:async';

        import 'package:angular2/angular2.dart';
        import 'package:angular2/src/reflection/reflection.dart' show reflector;
        import 'package:angular2/src/reflection/reflection_capabilities.dart' show ReflectionCapabilities;

        part 'show_properties.dart';
        part 'friends_service.dart';

        main() {
          reflector.reflectionCapabilities = new ReflectionCapabilities();
          bootstrap(DisplayComponent);
        }
    pre.prettyprint.lang-html(data-name="html")
      code.
        &lt;!-- web/index.html --&gt;
        &lt;!DOCTYPE html&gt;
        &lt;html&gt;
          &lt;head&gt;
            &lt;link rel=&quot;stylesheet&quot; href=&quot;style.css&quot;&gt;
          &lt;/head&gt;
          &lt;body&gt;

            &lt;display&gt;&lt;/display&gt;

            &lt;script type=&quot;application/dart&quot; src=&quot;main.dart&quot;&gt;&lt;/script&gt;
            &lt;script src=&quot;packages/browser/dart.js&quot;&gt;&lt;/script&gt;
          &lt;/body&gt;
        &lt;/html&gt;
    pre.prettyprint.lang-yaml(data-name="yaml")
      code.
        # pubspec.yaml
        name: displaying_data
        description: Dart version of Angular 2 example, Displaying Data
        version: 0.0.1
        dependencies:
          angular2: 2.0.0-alpha.21
          browser: any
.l-main-section
  h2#section-explanations Explanations

  .l-sub-section
    h3 Using multiple Dart files in an Angular app

      p.
        Dart offers a few ways to implement an app in multiple files.
        In this guide, all the code for each example is in a single library;
        each Dart file under <code>web</code> is part of that library.

      p.
        To let the code in <code>main.dart</code>
        use the code in <code>show_properties.dart</code>,
        declare a library in <code>main.dart</code>.
        Then make <code>show_properties.dart</code> part of that library.

      .code-box
        pre.prettyprint.lang-dart(data-name="main library file")
          code.
            // web/main.dart
            library displaying_data;
            // imports...
            part 'show_properties.dart';
            // Code goes here...
        pre.prettyprint.lang-dart(data-name="additional library file")
          code.
            // web/show_properties.dart
            part of displaying_data;
            // Code goes here...

      p.
        Another way to split Dart code is to
        define multiple libraries in a single package.
        The additional libraries go under a <code>lib</code> directory
        parallel to <code>web</code>.
        <!-- PENDING: show or point to an example -->

      p.
        Yet another approach, often used when some of the code is highly reusable,
        is to split the code into libraries in two or more packages.

      p.
        For more information on implementing Dart libraries, see
        <a href="https://www.dartlang.org/docs/dart-up-and-running/ch02.html#libraries-and-visibility">Libraries and visibility</a>
        in the
        <a href="https://www.dartlang.org/docs/dart-up-and-running/ch02.html">Dart language tour</a>.