467 lines
12 KiB
Markdown
467 lines
12 KiB
Markdown
@title
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Master/Detail
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@intro
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Build a master/detail page with a list of heroes.
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@description
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In this page, you'll expand the Tour of Heroes app to display a list of heroes, and
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allow users to select a hero and display the hero's details.
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When you're done with this page, the app should look like this <live-example></live-example>.
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## Where you left off
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Before you continue with this page of the Tour of Heroes,
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verify that you have the following structure after [The Hero Editor](tutorial/toh-pt1) page.
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If your structure doesn't match, go back to that page to figure out what you missed.
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<div class='filetree'>
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<div class='file'>
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angular-tour-of-heroes
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</div>
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<div class='children'>
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<div class='file'>
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src
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</div>
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<div class='children'>
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<div class='file'>
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app
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</div>
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<div class='children'>
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<div class='file'>
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app.component.ts
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</div>
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<div class='file'>
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app.module.ts
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</div>
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</div>
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<div class='file'>
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main.ts
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</div>
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<div class='file'>
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index.html
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</div>
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<div class='file'>
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styles.css
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</div>
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<div class='file'>
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systemjs.config.js
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</div>
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<div class='file'>
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tsconfig.json
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</div>
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</div>
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<div class='file'>
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node_modules ...
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</div>
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<div class='file'>
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package.json
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</div>
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</div>
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</div>
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## Keep the app transpiling and running
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Enter the following command in the terminal window:
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<code-example language="sh" class="code-shell">
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npm start
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</code-example>
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This command runs the TypeScript compiler in "watch mode", recompiling automatically when the code changes.
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The command simultaneously launches the app in a browser and refreshes the browser when the code changes.
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You can keep building the Tour of Heroes without pausing to recompile or refresh the browser.
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## Displaying heroes
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To display a list of heroes, you'll add heroes to the view's template.
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### Create heroes
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Create an array of ten heroes.
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<code-example path="toh-pt2/src/app/app.component.ts" region="hero-array" title="src/app/app.component.ts (hero array)">
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</code-example>
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The `HEROES` array is of type `Hero`, the class defined in the previous page.
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Eventually this app will fetch the list of heroes from a web service, but for now
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you can display mock heroes.
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### Expose heroes
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Create a public property in `AppComponent` that exposes the heroes for binding.
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<code-example path="toh-pt2/src/app/app.component.1.html" region="hero-array-1" title="app.component.ts (hero array property)">
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</code-example>
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The `heroes` type isn't defined because TypeScript infers it from the `HEROES` array.
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<div class="l-sub-section">
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The hero data is separated from the class implementation
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because ultimately the hero names will come from a data service.
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</div>
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### Display hero names in a template
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To display the hero names in an unordered list,
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insert the following chunk of HTML below the title and above the hero details.
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<code-example path="toh-pt2/src/app/app.component.1.html" region="heroes-template-1" title="app.component.ts (heroes template)" linenums="false">
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</code-example>
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Now you can fill the template with hero names.
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### List heroes with ngFor
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The goal is to bind the array of heroes in the component to the template, iterate over them,
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and display them individually.
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Modify the `<li>` tag by adding the built-in directive `*ngFor`.
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<code-example path="toh-pt2/src/app/app.component.1.html" region="heroes-ngfor-1" title="app.component.ts (ngFor)">
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</code-example>
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<div class="l-sub-section">
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The (`*`) prefix to `ngFor` is a critical part of this syntax.
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It indicates that the `<li>` element and its children
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constitute a master template.
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The `ngFor` directive iterates over the component's `heroes` array
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and renders an instance of this template for each hero in that array.
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The `let hero` part of the expression identifies `hero` as the template input variable,
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which holds the current hero item for each iteration.
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You can reference this variable within the template to access the current hero's properties.
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Read more about `ngFor` and template input variables in the
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[Showing an array property with *ngFor](guide/displaying-data#ngFor) section of the
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[Displaying Data](guide/displaying-data) page and the
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[ngFor](guide/template-syntax#ngFor) section of the
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[Template Syntax](guide/template-syntax) page.
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</div>
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Within the `<li>` tags, add content
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that uses the `hero` template variable to display the hero's properties.
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<code-example path="toh-pt2/src/app/app.component.1.html" region="ng-for" title="app.component.ts (ngFor template)" linenums="false">
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</code-example>
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When the browser refreshes, a list of heroes appears.
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### Style the heroes
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Users should get a visual cue of which hero they are hovering over and which hero is selected.
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To add styles to your component, set the `styles` property on the `@Component` decorator
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to the following CSS classes:
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<code-example path="toh-pt2/src/app/app.component.ts" region="styles" title="src/app/app.component.ts (styles)" linenums="false">
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</code-example>
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Remember to use the backtick notation for multi-line strings.
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Adding these styles makes the file much longer. In a later page you'll move the styles to a separate file.
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When you assign styles to a component, they are scoped to that specific component.
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These styles apply only to the `AppComponent` and don't affect the outer HTML.
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The template for displaying heroes should look like this:
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<code-example path="toh-pt2/src/app/app.component.1.html" region="heroes-styled" title="src/app/app.component.ts (styled heroes)" linenums="false">
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</code-example>
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## Selecting a hero
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The app now displays a list of heroes as well as a single hero in the details view. But
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the list and the details view are not connected.
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When users select a hero from the list, the selected hero should appear in the details view.
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This UI pattern is known as "master/detail."
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In this case, the _master_ is the heroes list and the _detail_ is the selected hero.
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Next you'll connect the master to the detail through a `selectedHero` component property,
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which is bound to a click event.
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### Handle click events
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Add a click event binding to the `<li>` like this:
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<code-example path="toh-pt2/src/app/app.component.1.html" region="selectedHero-click" title="app.component.ts (template excerpt)" linenums="false">
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</code-example>
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The parentheses identify the `<li>` element's `click` event as the target.
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The `onSelect(hero)` expression calls the `AppComponent` method, `onSelect()`,
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passing the template input variable `hero`, as an argument.
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That's the same `hero` variable you defined previously in the `ngFor` directive.
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<div class="l-sub-section">
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Learn more about event binding at the
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[User Input](guide/user-input) page and the
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[Event binding](guide/template-syntax#event-binding) section of the
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[Template Syntax](guide/template-syntax) page.
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</div>
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### Add a click handler to expose the selected hero
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You no longer need the `hero` property because you're no longer displaying a single hero; you're displaying a list of heroes.
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But the user will be able to select one of the heroes by clicking on it.
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So replace the `hero` property with this simple `selectedHero` property:
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<code-example path="toh-pt2/src/app/app.component.ts" region="selected-hero" title="src/app/app.component.ts (selectedHero)">
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</code-example>
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The hero names should all be unselected before the user picks a hero, so
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you won't initialize the `selectedHero` as you did with `hero`.
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Add an `onSelect()` method that sets the `selectedHero` property to the `hero` that the user clicks.
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<code-example path="toh-pt2/src/app/app.component.ts" region="on-select" title="src/app/app.component.ts (onSelect)" linenums="false">
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</code-example>
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The template still refers to the old `hero` property.
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Bind to the new `selectedHero` property instead as follows:
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<code-example path="toh-pt2/src/app/app.component.1.html" region="selectedHero-details" title="app.component.ts (template excerpt)" linenums="false">
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</code-example>
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### Hide the empty detail with ngIf
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When the app loads, `selectedHero` is undefined.
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The selected hero is initialized when the user clicks a hero's name.
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Angular can't display properties of the undefined `selectedHero` and throws the following error,
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visible in the browser's console:
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<code-example format="nocode">
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EXCEPTION: TypeError: Cannot read property 'name' of undefined in [null]
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</code-example>
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Although `selectedHero.name` is displayed in the template,
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you must keep the hero detail out of the DOM until there is a selected hero.
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Wrap the HTML hero detail content of the template with a `<div>`.
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Then add the `ngIf` built-in directive and set it to the `selectedHero` property of the component.
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<code-example path="toh-pt2/src/app/app.component.1.html" region="ng-if" title="src/app/app.component.ts (ngIf)" linenums="false">
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</code-example>
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<div class="alert is-critical">
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Don't forget the asterisk (`*`) in front of `ngIf`.
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</div>
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The app no longer fails and the list of names displays again in the browser.
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When there is no selected hero, the `ngIf` directive removes the hero detail HTML from the DOM.
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There are no hero detail elements or bindings to worry about.
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When the user picks a hero, `selectedHero` becomes defined and
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`ngIf` puts the hero detail content into the DOM and evaluates the nested bindings.
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<div class="l-sub-section">
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Read more about `ngIf` and `ngFor` in the
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[Structural Directives](guide/structural-directives) page and the
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[Built-in directives](guide/template-syntax#directives) section of the
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[Template Syntax](guide/template-syntax) page.
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</div>
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### Style the selected hero
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While the selected hero details appear below the list, it's difficult to identify the selected hero within the list itself.
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In the `styles` metadata that you added above, there is a custom CSS class named `selected`.
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To make the selected hero more visible, you'll apply this `selected` class to the `<li>` when the user clicks on a hero name.
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For example, when the user clicks "Magneta", it should render with a distinctive but subtle background color
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like this:
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<figure>
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<img src='generated/images/guide/toh/heroes-list-selected.png' alt="Selected hero">
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</figure>
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In the template, add the following `[class.selected]` binding to the `<li>`:
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<code-example path="toh-pt2/src/app/app.component.1.html" region="class-selected-1" title="app.component.ts (setting the CSS class)" linenums="false">
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</code-example>
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When the expression (`hero === selectedHero`) is `true`, Angular adds the `selected` CSS class.
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When the expression is `false`, Angular removes the `selected` class.
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<div class="l-sub-section">
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Read more about the `[class]` binding in the [Template Syntax](guide/template-syntax#ngClass "Template syntax: NgClass") guide.
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</div>
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The final version of the `<li>` looks like this:
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<code-example path="toh-pt2/src/app/app.component.1.html" region="class-selected-2" title="app.component.ts (styling each hero)" linenums="false">
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</code-example>
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After clicking "Magneta", the list should look like this:
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<figure>
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<img src='generated/images/guide/toh/heroes-list-1.png' alt="Output of heroes list app">
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</figure>
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Here's the complete `app.component.ts` as of now:
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<code-example path="toh-pt2/src/app/app.component.ts" title="src/app/app.component.ts">
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</code-example>
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## Summary
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Here's what you achieved in this page:
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* The Tour of Heroes app displays a list of selectable heroes.
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* You added the ability to select a hero and show the hero's details.
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* You learned how to use the built-in directives `ngIf` and `ngFor` in a component's template.
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Your app should look like this <live-example></live-example>.
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## Next step
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You've expanded the Tour of Heroes app, but it's far from complete.
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An app shouldn't be one monolithic component.
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In the [next page](tutorial/toh-pt3 "Multiple Components"), you'll split the app into subcomponents and make them work together.
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