angular-cn/aio/content/tutorial/toh-pt1.md

# The Hero Editor

The application now has a basic title.
Next you will create a new component to display hero information
and place that component in the application shell.

## Create the heroes component

Using the Angular CLI, generate a new component named `heroes`.

<code-example language="sh" class="code-shell">
  ng generate component heroes
</code-example>

The CLI creates a new folder, `src/app/heroes/` and generates
the three files of the  `HeroesComponent`.

The `HeroesComponent` class file is as follows:

<code-example 
  path="toh-pt1/src/app/heroes/heroes.component.ts" region="v1" 
  title="app/heroes/heroes.component.ts (initial version)" linenums="false">
</code-example>

You always import the `Component` symbol from the Angular core library
and annotate the component class with `@Component`.

`@Component` is a decorator function that specifies the Angular metadata for the component.

The CLI generated three metadata properties:

1. `selector`&mdash; the component's CSS element selector
1. `templateUrl`&mdash; the location of the component's template file.
1. `styleUrls`&mdash; the location of the component's private CSS styles.

{@a selector}

The [CSS element selector](https://developer.mozilla.org/en-US/docs/Web/CSS/Type_selectors),
`'app-heroes'`, matches the name of the HTML element that identifies this component within a parent component's template.

The `ngOnInit` is a [lifecycle hook](guide/lifecycle-hooks#oninit) 
Angular calls `ngOnInit` shortly after creating a component.
It's a good place to put initialization logic.

Always `export` the component class so you can `import` it elsewhere ... like in the `AppModule`.

### Add a _hero_ property

Add a `hero` property to the `HeroesComponent` for a hero named "Windstorm."

<code-example path="toh-pt1/src/app/heroes/heroes.component.ts" region="add-hero" title="heroes.component.ts (hero property)" linenums="false">
</code-example>

### Show the hero

Open the `heroes.component.html` template file.
Delete the default text generated by the Angular CLI and 
replace it with a data binding to the new `hero` property.  

<code-example path="toh-pt1/src/app/heroes/heroes.component.1.html" title="heroes.component.html" region="show-hero-1" linenums="false">
</code-example>

## Show the _HeroesComponent_ view

To display the `HeroesComponent`, you must add it to the template of the shell `AppComponent`.

Remember that `app-heroes` is the [element selector](#selector) for the `HeroesComponent`. 
So add an `<app-heroes>` element to the `AppComponent` template file, just below the title.

<code-example path="toh-pt1/src/app/app.component.html" title="src/app/app.component.html" linenums="false">
</code-example>

Assuming that the CLI `ng serve` command is still running,
the browser should refresh and display both the application title and the hero name.

## Create a Hero class

A real hero is more than a name.

Create a `Hero` class in its own file in the `src/app` folder.
Give it `id` and `name` properties.

<code-example path="toh-pt1/src/app/hero.ts"  title="src/app/hero.ts" linenums="false">
</code-example>


Return to the `HeroesComponent` class and import the `Hero` class.

Refactor the component's `hero` property to be of type `Hero`.
Initialize it with an `id` of `1` and the name `Windstorm`.

The revised `HeroesComponent` class file should look like this:

<code-example path="toh-pt1/src/app/heroes/heroes.component.ts" linenums="false"
  title= "src/app/heroes/heroes.component.ts">
</code-example>

The page no longer displays properly because you changed the hero from a string to an object.

## Show the hero object

Update the binding in the template to announce the hero's name
and show both `id` and `name` in a details layout like this:

<code-example 
  path="toh-pt1/src/app/heroes/heroes.component.1.html"
  region="show-hero-2" 
  title="heroes.component.html (HeroesComponent's template)" linenums="false">
</code-example>

The browser refreshes and display's the hero's information.

## Format with the _UppercasePipe_

Modify the `hero.name` binding like this.
<code-example
  path="toh-pt1/src/app/heroes/heroes.component.html"
  region="pipe">
</code-example>

The browser refreshes and now the hero's name is displayed in capital letters.

The word `uppercase` in the interpolation binding, 
right after the pipe operator ( | ),
activates the built-in `UppercasePipe`.

[Pipes](guide/pipes) are a good way to format strings, currency amounts, dates and other display data.
Angular ships with several built-in pipes and you can create your own.

## Edit the hero

Users should be able to edit the hero name in an `<input>` textbox.

The textbox should both _display_ the hero's `name` property
and _update_ that property as the user types.
That means data flow from the component class _out to the screen_ and
from the screen _back to the class_.

To automate that data flow, setup a two-way data binding between the `<input>` form element and the `hero.name` property.

### Two-way binding

Refactor the details area in the `HeroesComponent` template so it looks like this:

<code-example path="toh-pt1/src/app/heroes/heroes.component.1.html" region="name-input" title="src/app/heroes/heroes.component.html (HeroesComponent's template)" linenums="false">

</code-example>

**[(ngModel)]** is Angular's two-way data binding syntax. 

Here it binds the `hero.name` property to the HTML textbox so that data can flow _in both directions:_ from the `hero.name` property to the textbox, and from the textbox back to the `hero.name`.

### The missing _FormsModule_

Notice that the app stopped working when you added `[(ngModel)]`.

To see the error, open the browser development tools and look in the console
for a message like

<code-example language="sh" class="code-shell">
Template parse errors:
Can't bind to 'ngModel' since it isn't a known property of 'input'.
</code-example>

Although `ngModel` is a valid Angular directive, it isn't available by default. 

It belongs to the optional `FormsModule` and you must _opt-in_ to using it.

## _AppModule_

Angular needs to know how the pieces of your application fit together
and what other files and libraries the app requires.
This information is called _metadata_

Some of the metadata is in the `@Component` decorators that you added to your component classes.
Other critical metadata is in [`@NgModule`](guide/ngmodules) decorators.

The most important `@NgModule` decorator annotates the top-level **AppModule** class.

The Angular CLI generated an `AppModule` class in `src/app/app.module.ts` when it created the project.
This is where you _opt-in_ to the `FormsModule`.

### Import _FormsModule_

Open `AppModule` (`app.module.ts`) and import the `FormsModule` symbol from the `@angular/forms` library. 

<code-example path="toh-pt1/src/app/app.module.ts" title="app.module.ts (FormsModule symbol import)"
 region="formsmodule-js-import">
</code-example>

Then add `FormsModule` to the `@NgModule` metadata's `imports` array, which contains a list of external modules that the app needs.

<code-example path="toh-pt1/src/app/app.module.ts" title="app.module.ts ( @NgModule imports)"
region="ng-imports">
</code-example>

When the browser refreshes, the app should work again. You can edit the hero's name and see the changes reflected immediately in the `<h2>` above the textbox.

### Declare _HeroesComponent_ 

Every component must be declared in _exactly one_ [NgModule](guide/ngmodules).

_You_ didn't declare the `HeroesComponent`.
So why did the application work?

It worked because the Angular CLI declared `HeroesComponent` in the `AppModule` when it generated that component.

Open `src/app/app.module.ts` and find `HeroesComponent` imported near the top.
<code-example path="toh-pt1/src/app/app.module.ts" region="heroes-import" >
</code-example>

The `HeroesComponent` is declared in the `@NgModule.declarations` array.
<code-example path="toh-pt1/src/app/app.module.ts" region="declarations">
</code-example>

Note that `AppModule`  declares both application components, `AppComponent` and `HeroesComponent`.


## Final code review

Your app should look like this <live-example></live-example>. Here are the code files discussed on this page.

<code-tabs>

  <code-pane title="src/app/heroes/heroes.component.ts" path="toh-pt1/src/app/heroes/heroes.component.ts">
  </code-pane>

  <code-pane title="src/app/heroes/heroes.component.html" path="toh-pt1/src/app/heroes/heroes.component.html">
  </code-pane>

  <code-pane title="src/app/app.module.ts" 
  path="toh-pt1/src/app/app.module.ts">
  </code-pane>

  <code-pane title="src/app/app.component.ts" path="toh-pt1/src/app/app.component.ts">
  </code-pane>

  <code-pane title="src/app/app.component.html" path="toh-pt1/src/app/app.component.html">
  </code-pane>

  <code-pane title="src/app/hero.ts" 
  path="toh-pt1/src/app/hero.ts">
  </code-pane>

</code-tabs>

## Summary

* You used the CLI to create a second `HeroesComponent`.
* You displayed the `HeroesComponent` by adding it to the `AppComponent` shell. 
* You applied the `UppercasePipe` to format the name.
* You used two-way data binding with the `ngModel` directive.
* You learned about the `AppModule`.
* You imported the `FormsModule` in the `AppModule` so that Angular would recognize and apply the `ngModel` directive. 
* You learned the importance of declaring components in the `AppModule`
and appreciated that the CLI declared it for you.