angular-cn/aio/content/guide/event-binding.md

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# Event binding
Event binding allows you to listen for and respond to user actions such as keystrokes, mouse movements, clicks, and touches.
<div class="alert is-helpful">
See the <live-example></live-example> for a working example containing the code snippets in this guide.
</div>
## Binding to events
To bind to an event you use the Angular event binding syntax.
This syntax consists of a target event name within parentheses to the left of an equal sign, and a quoted template statement to the right.
In the following example, the target event name is `click` and the template statement is `onSave()`.
<code-example language="html" header="Event binding syntax">
&lt;button (click)="onSave()"&gt;Save&lt;/button&gt;
</code-example>
The event binding listens for the button's click events and calls the component's `onSave()` method whenever a click occurs.
<div class="lightbox">
<img src='generated/images/guide/template-syntax/syntax-diagram.svg' alt="Syntax diagram">
</div>
## Custom events with `EventEmitter`
[Directives](guide/built-in-directives) typically raise custom events with an Angular [EventEmitter](api/core/EventEmitter) as follows.
1. The directive creates an `EventEmitter` and exposes it as a property.
1. The directive then calls `EventEmitter.emit(data)` to emit an event, passing in message data, which can be anything.
1. Parent directives listen for the event by binding to this property and accessing the data through the `$event` object.
Consider an `ItemDetailComponent` that presents item information and responds to user actions.
Although the `ItemDetailComponent` has a delete button, it doesn't contain the functionality to delete the hero.
It can only raise an event reporting the user's delete request.
<code-example path="event-binding/src/app/item-detail/item-detail.component.html" header="src/app/item-detail/item-detail.component.html (template)" region="line-through"></code-example>
The component defines a `deleteRequest` property that returns an `EventEmitter`.
When the user clicks **Delete**, the component invokes the `delete()` method, telling the `EventEmitter` to emit an `Item` object.
<code-example path="event-binding/src/app/item-detail/item-detail.component.ts" header="src/app/item-detail/item-detail.component.ts (deleteRequest)" region="deleteRequest"></code-example>
The hosting parent component binds to the `deleteRequest` event of the `ItemDetailComponent` as follows.
<code-example path="event-binding/src/app/app.component.html" header="src/app/app.component.html (event-binding-to-component)" region="event-binding-to-component"></code-example>
When the `deleteRequest` event fires, Angular calls the parent component's `deleteItem()` method with the item.
### Determining an event target
To determine an event target, Angular checks if the name of the target event matches an event property of a known directive.
In the following example, Angular checks to see if `myClick` is an event on the custom `ClickDirective`.
<code-example path="event-binding/src/app/app.component.html" region="custom-directive" header="src/app/app.component.html"></code-example>
If the target event name, `myClick` fails to match an element event or an output property of `ClickDirective`, Angular reports an "unknown directive" error.
## What's next
For more information on how event binding works, see [How event binding works](guide/event-binding-concepts).