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='/resources/images/examples/displaying-data-example1.png' alt="Example of Todo App")

.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-tabs
    code-pane(language="dart" name="web/main.dart" format="linenums").
      import 'package:angular2/bootstrap.dart';
      import 'package:displaying_data/show_properties.dart';

      main() {
        bootstrap(DisplayComponent);
      }
    code-pane(language="html" name="web/index.html" format="linenums").
      &lt;!DOCTYPE html&gt;
      &lt;html&gt;
        &lt;head&gt;
          &lt;title&gt;Displaying Data&lt;/title&gt;
          &lt;link rel=&quot;stylesheet&quot; href=&quot;style.css&quot;&gt;
          &lt;script async src=&quot;main.dart&quot; type=&quot;application/dart&quot;&gt;&lt;/script&gt;
          &lt;script async src=&quot;packages/browser/dart.js&quot;&gt;&lt;/script&gt;
        &lt;/head&gt;
        &lt;body&gt;
          &lt;display&gt;&lt;/display&gt;
        &lt;/body&gt;
      &lt;/html&gt;
    code-pane(language="yaml" name="pubspec.yaml" format="linenums").
      name: displaying_data
      description: Dart version of Angular 2 example, Displaying Data
      version: 0.0.1
      dependencies:
        angular2: 2.0.0-alpha.39
        browser: ^0.10.0
      transformers:
      - angular2:
          entry_points: web/main.dart
  p.
   All of this code should look familiar from the previous page,
   except for the imports in <code>main.dart</code>.
   The import of <code>show_properties.dart</code>
   lets you implement part of the app in a different Dart file.
   You've previously seen <code>angular2.dart</code> imported,
   but that's unnecessary here because this version of <code>main.dart</code>
   doesn't implement any components or other injectable types.

  p.
   All three of these files remain similar in the rest of the examples,
   so we'll focus on what changes.

.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 ng-non-bindable="">{{ }}</strong>.

  p.
    To see this working, first create a <code>lib</code> directory.
    Under it, put a Dart file named <code>show_properties.dart</code>
    that contains the following code:

  code-example(language="dart" format="linenums" escape="html").
    // lib/show_properties.dart
    library displaying_data.show_properties;

    import 'package:angular2/angular2.dart';

    @Component(selector: 'display')
    @View(template: '''
    <p>My name: {{ myName }}</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:

  code-example(language="html" escape="html").
    <p>My name: {{ myName }}</p>

  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:

  code-example(language="html").
    &lt;p&gt;Current time: {{ time }}&lt;/p&gt;

  p.
    Then import <code>dart:async</code> so you can use a Timer,
    and give the <code>DisplayComponent</code> a starting value for time and
    create a periodic Timer call to update the time:

  code-example(language="dart").
    import 'dart:async';
    ...
    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 *ng-for
  p Moving up from a single value, create a property that's a list of values.

  code-example(language="dart").
    class DisplayComponent {
      String myName = 'Alice';
      List&lt;String&gt; friendNames = const [
        'Aarav',
        'Martín',
        'Shannon',
        'Ariana',
        'Kai'
      ];
    }

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

  code-example(language="dart").
    @View(template: '''
    &lt;p&gt;My name: {{ myName }}&lt;/p&gt;
    &lt;p&gt;Friends:&lt;/p&gt;
    &lt;ul&gt;
       &lt;li <span class="pnk">*ng-for="#name of friendNames"</span>&gt;
          {{ name }}
       &lt;/li&gt;
    &lt;/ul&gt;
    ''', <span class="pnk">directives: const [NgFor]</span>)

  p.
    To make <code>ng-for</code> work,
    you need to add the Angular <code>NgFor</code> directive,
    so that Angular knows to include it.
    Add <code>NgFor</code> using the optional <code>directives</code> parameter.

  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:

  code-example(language="html").
    &lt;li *ng-for=&quot;#name of friendNames&quot;&gt;
       {{ name }}
    &lt;/li&gt;

  p The way to read this is:
  ul
    li.
      <code>*ng-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.
    Put this in a new file under <code>lib/</code>
    named <code>friends_service.dart</code>. Here's what the class looks like:

  code-example(language="dart" format="linenums").
    // lib/friends_service.dart
    library displaying_data.friends_service;

    import 'package:angular2/angular2.dart';

    @Injectable()
    class FriendsService {
      List&lt;String&gt; names = ['Aarav', 'Martín', 'Shannon', 'Ariana', 'Kai'];
    }

  p.
    Now you can replace the current list of friends in DisplayComponent.
    Import <code>friends_service.dart</code>,
    and add a FriendsService parameter to the constructor.
    Then set <code>friendNames</code> to the names provided by the service.

  code-example(language="dart").
    // In lib/show_properties.dart
    ...
    <span class="pnk">import 'package:displaying_data/friends_service.dart';</span>
    ...
    class DisplayComponent {
      String myName = 'Alice';
      List&lt;String&gt; friendNames;

      DisplayComponent(<span class="pnk">FriendsService friendsService</span>) {
        <span class="pnk">friendNames = friendsService.names;</span>
      }
    }

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

  code-example(language="dart").
    @Component(selector: 'display', <span class="pnk">viewBindings: const [FriendsService]</span>)

.l-main-section
  h2#Conditionally-displaying-data-with-NgIf Conditionally display data using *ng-if
  p.
    Lastly, before we move on, let's handle showing parts of our UI conditionally with <code>*ng-if</code>.  The
    <code>NgIf</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:

  code-example(language="html").
    &lt;p *ng-if="friendNames.length &gt; 3"&gt;You have many friends!&lt;/p&gt;

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

  code-example(language="dart").
    directives: const[NgFor, <span class="pnk">NgIf</span>]
  p.
    The list currently 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.

  p Here's the final code.

  code-tabs
    code-pane(language="dart" name="lib/show_properties.dart" format="linenums").
      library displaying_data.show_properties;

      import 'package:angular2/angular2.dart';
      import 'package:displaying_data/friends_service.dart';

      @Component(selector: 'display', viewBindings: const [FriendsService])
      @View(template: '''
      &lt;p&gt;My name: {{ myName }}&lt;/p&gt;
      &lt;p&gt;Friends:&lt;/p&gt;
      &lt;ul&gt;
         &lt;li *ng-for="#name of friendNames"&gt;
            {{ name }}
         &lt;/li&gt;
      &lt;/ul&gt;
      &lt;p *ng-if="friendNames.length &gt; 3"&gt;You have many friends!&lt;/p&gt;
      ''', directives: const [NgFor, NgIf])
      class DisplayComponent {
        String myName = 'Alice';
        List&lt;String&gt; friendNames;

        DisplayComponent(FriendsService friendsService) {
          friendNames = friendsService.names;
        }
      }
    code-pane(language="dart" name="lib/friends_service.dart" format="linenums").
      library displaying_data.friends_service;

      import 'package:angular2/angular2.dart';

      @Injectable()
      class FriendsService {
        List&lt;String&gt; names = ['Aarav', 'Martín', 'Shannon', 'Ariana', 'Kai'];
      }
    code-pane(language="dart" name="web/main.dart" format="linenums").
      import 'package:angular2/bootstrap.dart';
      import 'package:displaying_data/show_properties.dart';

      main() {
        bootstrap(DisplayComponent);
      }
    code-pane(language="html" name="web/index.html" format="linenums").
      &lt;!DOCTYPE html&gt;
      &lt;html&gt;
        &lt;head&gt;
          &lt;title&gt;Displaying Data&lt;/title&gt;
          &lt;link rel=&quot;stylesheet&quot; href=&quot;style.css&quot;&gt;
          &lt;script async src=&quot;main.dart&quot; type=&quot;application/dart&quot;&gt;&lt;/script&gt;
          &lt;script async src=&quot;packages/browser/dart.js&quot;&gt;&lt;/script&gt;
        &lt;/head&gt;
        &lt;body&gt;
          &lt;display&gt;&lt;/display&gt;
        &lt;/body&gt;
      &lt;/html&gt;
    code-pane(language="yaml" name="pubspec.yaml" format="linenums").
      name: displaying_data
      description: Displaying Data example
      version: 0.0.1
      dependencies:
        angular2: 2.0.0-alpha.39
        browser: ^0.10.0
      transformers:
      - angular2:
          entry_points: web/main.dart
.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, each example is in a single package,
      and each Dart file implements a separate library.
      For a bigger project, you might split the code into libraries
      in two or more packages.

    p.
      To use the API defined in <code>show_properties.dart</code>,
      <code>main.dart</code> must import that file.
      The import statement uses the package name
      (defined in <code>pubspec.yaml</code> to be <b>displaying_data</b>)
      and the path to <code>show_properties.dart</code>
      (starting at the app's top directory,
      but omitting the <code>lib/</code> directory).

    code-example(language="dart").
      // In web/main.dart:
      ...
      import 'package:displaying_data/show_properties.dart';
      ...

      // In lib/show_properties.dart:
      library displaying_data.show_properties;
      ...

    p.
      The name that <code>show_properties.dart</code> specifies for its library
      is similar to the path used to import the library,
      but with no ".dart" suffix and
      with dots (<code>.</code>) instead of slashes (<code>/</code>).
      <a href="https://www.dartlang.org/articles/style-guide/#do-name-libraries-and-source-files-using-lowercasewithunderscores">Naming
      conventions for libraries</a>,
      along with lots of other helpful information, are in the
      <a href="https://www.dartlang.org/articles/style-guide/">Dart Style Guide</a>.

    p.
      Another import lets <code>show_properties.dart</code>
      use the API defined in <code>friends_service.dart</code>:

    code-example(language="dart").
      // In lib/show_properties.dart:
      library displaying_data.show_properties;
      ...
      import 'package:displaying_data/friends_service.dart';
      ...

      // In lib/friends_service.dart:
      library displaying_data.friends_service;
      ...

    p.
      Because both <code>show_properties.dart</code> and <code>friends_service.dart</code>
      are under <code>lib</code>,
      the import could instead use a relative path:

    code-example(language="dart").
      // In lib/show_properties.dart:
      library displaying_data.show_properties;
      ...
      import 'friends_service.dart';
      ...

      // In lib/friends_service.dart:
      library displaying_data.friends_service;
      ...

    p.
      The app's entry point—<code>main.dart</code>—imports
      <code>bootstrap.dart</code> so that it can call <code>bootstrap()</code>.
      Both <code>show_properties.dart</code> and <code>friends_service.dart</code>
      import <code>angular2.dart</code>
      so that they can define Angular components and models.

    code-example(language="dart").
      // In web/main.dart:
      import 'package:angular2/bootstrap.dart';
      ...
      bootstrap(...)
      ...

      // In lib/show_properties.dart:
      ...
      import 'package:angular2/angular2.dart';
      ...
      @Component(...)
      @View(...)
      ...

      // In lib/friends_service.dart:
      ...
      import 'package:angular2/angular2.dart';
      ...
      @Injectable()
      ...


    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>.