toh-pt2.md
# Display a Heroes List
In this page, you'll expand the Tour of Heroes app to display a list of heroes, and
allow users to select a hero and display the hero's details.
## Create mock heroes
You'll need some heroes to display.
Eventually you'll get them from a remote data server.
For now, you'll create some _mock heroes_ and pretend they came from the server.
Create a file called `mock-heroes.ts` in the `src/app/` folder.
Define a `HEROES` constant as an array of ten heroes and export it.
The file should look like this.
<code-example path="toh-pt2/src/app/mock-heroes.ts" linenums="false"
title="src/app/mock-heroes.ts">
</code-example>
## Displaying heroes
You're about to display the list of heroes at the top of the `HeroesComponent`.
Open the `HeroesComponent` class file and import the mock `HEROES`.
<code-example path="toh-pt2/src/app/heroes/heroes.component.ts" region="import-heroes" title="src/app/heroes/heroes.component.ts (import HEROES)">
</code-example>
Add a `heroes` property to the class that exposes these heroes for binding.
<code-example path="toh-pt2/src/app/heroes/heroes.component.ts" region="heroes">
</code-example>
### List heroes with _*ngFor_
Open the `HeroesComponent` template file and make the following changes:
* Add an `<h2>` at the top,
* Below it add an HTML unordered list (`<ul>`)
* Insert an `<li>` within the `<ul>` that displays properties of a `hero`.
* Sprinkle some CSS classes for styling (you'll add the CSS styles shortly).
Make it look like this:
<code-example path="toh-pt2/src/app/heroes/heroes.component.1.html" region="list" title="heroes.component.html (heroes template)" linenums="false">
</code-example>
Now change the `<li>` to this:
<code-example path="toh-pt2/src/app/heroes/heroes.component.1.html" region="li">
</code-example>
The [`*ngFor`](guide/template-syntax#ngFor) is Angular's _repeater_ directive.
It repeats the host element for each element in a list.
In this example
* `<li>` is the host element
* `heroes` is the list from the `HeroesComponent` class.
* `hero` holds the current hero object for each iteration through the list.
<div class="alert is-important">
Don't forget the asterisk (*) in front of `ngFor`. It's a critical part of the syntax.
</div>
After the browser refreshes, the list of heroes appears.
{@a styles}
### Style the heroes
The heroes list should be attractive and should respond visually when users
hover over and select a hero from the list.
In the [first tutorial](tutorial/toh-pt0#app-wide-styles), you set the basic styles for the entire application in `styles.css`.
That stylesheet didn't include styles for this list of heroes.
You could add more styles to `styles.css` and keep growing that stylesheet as you add components.
You may prefer instead to define private styles for a specific component and keep everything a component needs— the code, the HTML,
and the CSS —together in one place.
This approach makes it easier to re-use the component somewhere else
and deliver the component's intended appearance even if the global styles are different.
You define private styles either inline in the `@Component.styles` array or
as stylesheet file(s) identified in the `@Component.styleUrls` array.
When the CLI generated the `HeroesComponent`, it created an empty `heroes.component.css` stylesheet for the `HeroesComponent`
and pointed to it in `@Component.styleUrls` like this.
<code-example path="toh-pt2/src/app/heroes/heroes.component.ts" region="metadata"
title="src/app/heroes/heroes.component.ts (@Component)">
</code-example>
Open the `heroes.component.css` file and paste in the private CSS styles for the `HeroesComponent`.
You'll find them in the [final code review](#final-code-review) at the bottom of this guide.
<div class="alert is-important">
Styles and stylesheets identified in `@Component` metadata are scoped to that specific component.
The `heroes.component.css` styles apply only to the `HeroesComponent` and don't affect the outer HTML or the HTML in any other component.
</div>
## Master/Detail
When the user clicks a hero in the **master** list,
the component should display the selected hero's **details** at the bottom of the page.
In this section, you'll listen for the hero item click event
and update the hero detail.
### Add a click event binding
Add a click event binding to the `<li>` like this:
<code-example path="toh-pt2/src/app/heroes/heroes.component.1.html" region="selectedHero-click" title="heroes.component.html (template excerpt)" linenums="false">
</code-example>
This is an example of Angular's [event binding](guide/template-syntax#event-binding) syntax.
The parentheses around `click` tell Angular to listen for the `<li>` element's `click` event.
When the user clicks in the `<li>`, Angular executes the `onSelect(hero)` expression.
`onSelect()` is a `HeroesComponent` method that you're about to write.
Angular calls it with the `hero` object displayed in the clicked `<li>`,
the same `hero` defined previously in the `*ngFor` expression.
### Add the click event handler
Rename the component's `hero` property to `selectedHero` but don't assign it.
There is no _selected hero_ when the application starts.
Add the following `onSelect()` method, which assigns the clicked hero from the template
to the component's `selectedHero`.
<code-example path="toh-pt2/src/app/heroes/heroes.component.ts" region="on-select" title="src/app/heroes/heroes.component.ts (onSelect)" linenums="false">
</code-example>
### Update the details template
The template still refers to the component's old `hero` property which no longer exists.
Rename `hero` to `selectedHero`.
<code-example path="toh-pt2/src/app/heroes/heroes.component.html" region="selectedHero-details" title="heroes.component.html (selected hero details)" linenums="false">
</code-example>
### Hide empty details with _*ngIf_
After the browser refreshes, the application is broken.
Open the browser developer tools and look in the console for an error message like this:
<code-example language="sh" class="code-shell">
HeroesComponent.html:3 ERROR TypeError: Cannot read property 'name' of undefined
</code-example>
Now click one of the list items.
The app seems to be working again.
The heroes appear in a list and details about the clicked hero appear at the bottom of the page.
#### What happened?
When the app starts, the `selectedHero` is `undefined` _by design_.
Binding expressions in the template that refer to properties of `selectedHero` — expressions like `{{selectedHero.name}}` — _must fail_ because there is no selected hero.
#### The fix
The component should only display the selected hero details if the `selectedHero` exists.
Wrap the hero detail HTML in a `<div>`.
Add Angular's `*ngIf` directive to the `<div>` and set it to `selectedHero`.
<div class="alert is-important">
Don't forget the asterisk (*) in front of `ngIf`. It's a critical part of the syntax.
</div>
<code-example path="toh-pt2/src/app/heroes/heroes.component.html" region="ng-if" title="src/app/heroes/heroes.component.html (*ngIf)" linenums="false">
</code-example>
After the browser refreshes, the list of names reappears.
The details area is blank.
Click a hero and its details appear.
#### Why it works
When `selectedHero` is undefined, the `ngIf` removes the hero detail from the DOM. There are no `selectedHero` bindings to worry about.
When the user picks a hero, `selectedHero` has a value and
`ngIf` puts the hero detail into the DOM.
### Style the selected hero
It's difficult to identify the _selected hero_ in the list when all `<li>` elements look alike.
If the user clicks "Magneta", that hero should render with a distinctive but subtle background color like this:
<figure>
<img src='generated/images/guide/toh/heroes-list-selected.png' alt="Selected hero">
</figure>
That _selected hero_ coloring is the work of the `.selected` CSS class in the [styles you added earlier](#styles).
You just have to apply the `.selected` class to the `<li>` when the user clicks it.
The Angular [class binding](guide/template-syntax#class-binding) makes it easy to add and remove a CSS class conditionally.
Just add `[class.some-css-class]="some-condition"` to the element you want to style.
Add the following `[class.selected]` binding to the `<li>` in the `HeroesComponent` template:
<code-example path="toh-pt2/src/app/heroes/heroes.component.1.html" region="class-selected" title="heroes.component.html (toggle the 'selected' CSS class)" linenums="false">
</code-example>
When the current row hero is the same as the `selectedHero`, Angular adds the `selected` CSS class. When the two heroes are different, Angular removes the class.
The finished `<li>` looks like this:
<code-example path="toh-pt2/src/app/heroes/heroes.component.html" region="li" title="heroes.component.html (list item hero)" linenums="false">
</code-example>
{@a final-code-review}
## Final code review
Your app should look like this <live-example></live-example>.
Here are the code files discussed on this page, including the `HeroesComponent` styles.
<code-tabs>
<code-pane title="src/app/heroes/heroes.component.ts" path="toh-pt2/src/app/heroes/heroes.component.ts">
</code-pane>
<code-pane title="src/app/heroes/heroes.component.html" path="toh-pt2/src/app/heroes/heroes.component.html">
</code-pane>
<code-pane title="src/app/heroes/heroes.component.css" path="toh-pt2/src/app/heroes/heroes.component.css">
</code-pane>
</code-tabs>
## Summary
* The Tour of Heroes app displays a list of heroes in a Master/Detail view.
* The user can select a hero and see that hero's details.
* You used `*ngFor` to display a list.
* You used `*ngIf` to conditionally include or exclude a block of HTML.
* You can toggle a CSS style class with a `class` binding.
