161 lines
6.4 KiB
Markdown
161 lines
6.4 KiB
Markdown
# Master/Detail Components
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At the moment, the `HeroesComponent` displays both the list of heroes and the selected hero's details.
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Keeping all features in one component as the application grows will not be maintainable.
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You'll want to split up large components into smaller sub-components, each focused on a specific task or workflow.
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In this page, you'll take the first step in that direction by moving the hero details into a separate, reusable `HeroDetailComponent`.
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The `HeroesComponent` will only present the list of heroes.
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The `HeroDetailComponent` will present details of a selected hero.
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## Make the `HeroDetailComponent`
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Use the Angular CLI to generate a new component named `hero-detail`.
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<code-example language="sh" class="code-shell">
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ng generate component hero-detail
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</code-example>
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The command scaffolds the `HeroDetailComponent` files and declares the component in `AppModule`.
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### Write the template
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Cut the HTML for the hero detail from the bottom of the `HeroesComponent` template and paste it over the generated boilerplate in the `HeroDetailComponent` template.
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The pasted HTML refers to a `selectedHero`.
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The new `HeroDetailComponent` can present _any_ hero, not just a selected hero.
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So replace "selectedHero" with "hero" everywhere in the template.
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When you're done, the `HeroDetailComponent` template should look like this:
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<code-example path="toh-pt3/src/app/hero-detail/hero-detail.component.html" title="src/app/hero-detail/hero-detail.component.html" linenums="false">
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</code-example>
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### Add the `@Input()` hero property
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The `HeroDetailComponent` template binds to the component's `hero` property
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which is of type `Hero`.
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Open the `HeroDetailComponent` class file and import the `Hero` symbol.
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<code-example path="toh-pt3/src/app/hero-detail/hero-detail.component.ts"
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region="import-hero" title="src/app/hero-detail/hero-detail.component.ts (import Hero)">
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</code-example>
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The `hero` property
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[must be an _Input_ property](guide/template-syntax#inputs-outputs "Input and Output properties"),
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annotated with the `@Input()` decorator,
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because the _external_ `HeroesComponent` [will bind to it](#heroes-component-template) like this.
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<code-example path="toh-pt3/src/app/heroes/heroes.component.html" region="hero-detail-binding">
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</code-example>
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Amend the `@angular/core` import statement to include the `Input` symbol.
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<code-example path="toh-pt3/src/app/hero-detail/hero-detail.component.ts" region="import-input" title="src/app/hero-detail/hero-detail.component.ts (import Input)" linenums="false">
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</code-example>
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Add a `hero` property, preceded by the `@Input()` decorator.
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<code-example path="toh-pt3/src/app/hero-detail/hero-detail.component.ts" region="input-hero" linenums="false">
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</code-example>
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That's the only change you should make to the `HeroDetailComponent` class.
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There are no more properties. There's no presentation logic.
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This component simply receives a hero object through its `hero` property and displays it.
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## Show the `HeroDetailComponent`
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The `HeroesComponent` is still a master/detail view.
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It used to display the hero details on its own, before you cut that portion of the template. Now it will delegate to the `HeroDetailComponent`.
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The two components will have a parent/child relationship.
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The parent `HeroesComponent` will control the child `HeroDetailComponent`
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by sending it a new hero to display whenever
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the user selects a hero from the list.
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You won't change the `HeroesComponent` _class_ but you will change its _template_.
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{@a heroes-component-template}
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### Update the `HeroesComponent` template
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The `HeroDetailComponent` selector is `'app-hero-detail'`.
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Add an `<app-hero-detail>` element near the bottom of the `HeroesComponent` template, where the hero detail view used to be.
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Bind the `HeroesComponent.selectedHero` to the element's `hero` property like this.
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<code-example path="toh-pt3/src/app/heroes/heroes.component.html" region="hero-detail-binding" title="heroes.component.html (HeroDetail binding)">
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</code-example>
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`[hero]="selectedHero"` is an Angular [property binding](guide/template-syntax#property-binding).
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It's a _one way_ data binding from
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the `selectedHero` property of the `HeroesComponent` to the `hero` property of the target element, which maps to the `hero` property of the `HeroDetailComponent`.
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Now when the user clicks a hero in the list, the `selectedHero` changes.
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When the `selectedHero` changes, the _property binding_ updates `hero`
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and the `HeroDetailComponent` displays the new hero.
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The revised `HeroesComponent` template should look like this:
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<code-example path="toh-pt3/src/app/heroes/heroes.component.html"
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title="heroes.component.html" linenums="false">
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</code-example>
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The browser refreshes and the app starts working again as it did before.
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## What changed?
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As [before](tutorial/toh-pt2), whenever a user clicks on a hero name,
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the hero detail appears below the hero list.
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Now the `HeroDetailComponent` is presenting those details instead of the `HeroesComponent`.
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Refactoring the original `HeroesComponent` into two components yields benefits, both now and in the future:
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1. You simplified the `HeroesComponent` by reducing its responsibilities.
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1. You can evolve the `HeroDetailComponent` into a rich hero editor
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without touching the parent `HeroesComponent`.
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1. You can evolve the `HeroesComponent` without touching the hero detail view.
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1. You can re-use the `HeroDetailComponent` in the template of some future component.
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## Final code review
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Here are the code files discussed on this page and your app should look like this <live-example></live-example>.
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<code-tabs>
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<code-pane title="src/app/hero-detail/hero-detail.component.ts" path="toh-pt3/src/app/hero-detail/hero-detail.component.ts">
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</code-pane>
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<code-pane title="src/app/hero-detail/hero-detail.component.html" path="toh-pt3/src/app/hero-detail/hero-detail.component.html">
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</code-pane>
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<code-pane title="src/app/heroes/heroes.component.html" path="toh-pt3/src/app/heroes/heroes.component.html">
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</code-pane>
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<code-pane title="src/app/app.module.ts" path="toh-pt3/src/app/app.module.ts">
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</code-pane>
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</code-tabs>
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## Summary
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* You created a separate, reusable `HeroDetailComponent`.
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* You used a [property binding](guide/template-syntax#property-binding) to give the parent `HeroesComponent` control over the child `HeroDetailComponent`.
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* You used the [`@Input` decorator](guide/template-syntax#inputs-outputs)
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to make the `hero` property available for binding
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by the external `HeroesComponent`.
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