docs(attribute-directive): new chapter + dev-guide chapter shuffle

closes #437
This commit is contained in:
Deborah Kurata 2015-11-19 16:59:22 -08:00 committed by Ward Bell
parent af105bb354
commit c9ea1e52c1
18 changed files with 515 additions and 10 deletions

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src/**/*.js

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{
"name": "angular2-attribute-directive",
"version": "1.0.0",
"description": "",
"main": "index.js",
"scripts": {
"tsc": "tsc -p src -w",
"start": "live-server --open=src"
},
"keywords": [],
"author": "",
"license": "ISC",
"dependencies": {
"angular2": "2.0.0-alpha.47",
"systemjs": "0.19.6"
},
"devDependencies": {
"live-server": "^0.8.2",
"typescript": "^1.6.2"
}
}

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<!-- #docregion -->
<h1>My First Attribute Directive</h1>
<span my-highlight>Highlight me!</span>
<!-- #enddocregion -->

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<!-- #docregion -->
<h1>My First Attribute Directive</h1>
<h4>Pick a highlight color</h4>
<div>
<input type="radio" name="colors" (click)="color='lightgreen'">Green
<input type="radio" name="colors" (click)="color='yellow'">Yellow
<input type="radio" name="colors" (click)="color='cyan'">Cyan
</div>
<!-- #docregion span -->
<p><span [my-highlight]="color">Highlight me!</span></p>
<!-- #enddocregion span -->
<!-- #enddocregion -->

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// #docregion
import {Component} from 'angular2/angular2';
import {Highlight} from './highlight.directive'
@Component({
selector: 'my-app',
templateUrl: 'app/app.component.html',
directives: [Highlight]
})
export class AppComponent { }
// #enddocregion

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// #docregion
import {bootstrap} from 'angular2/angular2';
import {AppComponent} from './app.component';
bootstrap(AppComponent);

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// #docregion
import {Directive, ElementRef, Renderer, Input} from 'angular2/angular2';
@Directive({
selector: '[my-highlight]'
})
export class Highlight {
constructor(el: ElementRef, renderer: Renderer) {
//el.nativeElement.style.backgroundColor = 'yellow';
renderer.setElementStyle(el, 'background-color', 'yellow');
}
}
// #enddocregion

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// #docregion
import {Directive, ElementRef, Renderer, Input} from 'angular2/angular2';
@Directive({
selector: '[my-highlight]',
// #docregion host
host: {
'(mouseenter)': 'onMouseEnter()',
'(mouseleave)': 'onMouseLeave()'
}
// #enddocregion host
})
export class Highlight {
// #docregion ctor
constructor(private el: ElementRef, private renderer: Renderer) {
}
// #enddocregion ctor
// #docregion mouse-methods
onMouseEnter() { this._highlight("yellow"); }
onMouseLeave() { this._highlight(null); }
private _highlight(color: string) {
this.renderer.setElementStyle(this.el, 'background-color', color);
}
// #enddocregion mouse-methods
}
// #enddocregion

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// #docplaster
// #docregion full
import {Directive, ElementRef, Renderer, Input} from 'angular2/angular2';
@Directive({
selector: '[my-highlight]',
host: {
'(mouseenter)': 'onMouseEnter()',
'(mouseleave)': 'onMouseLeave()'
}
})
// #docregion class
export class Highlight {
// #enddocregion class
// #enddocregion full
/*
// #docregion highlight
@Input() myHighlight: string;
// #enddocregion highlight
*/
// #docregion full
// #docregion class
// #docregion color
@Input('my-highlight') highlightColor: string;
// #enddocregion color
private _defaultColor = 'red';
constructor(private el: ElementRef, private renderer: Renderer) { }
// #docregion mouse-enter
onMouseEnter() { this._highlight(this.highlightColor || this._defaultColor); }
// #enddocregion mouse-enter
onMouseLeave() { this._highlight(null); }
private _highlight(color:string) {
this.renderer.setElementStyle(this.el, 'background-color', color);
}
}
// #enddocregion class
// #enddocregion full

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<!-- #docregion -->
<!DOCTYPE html>
<html>
<head>
<title>Attribute Directives</title>
<script src="../node_modules/systemjs/dist/system.src.js"></script>
<script src="../node_modules/angular2/bundles/angular2.dev.js"></script>
<script>
System.config({
packages: {'app': {defaultExtension: 'js'}}
});
System.import('app/boot');
</script>
</head>
<body>
<my-app>loading...</my-app>
</body>
</html>

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{
"description": "Attribute Directive",
"files":[
"!**/*.d.ts",
"!**/*.js",
"!app/*.[1,2].*"
],
"tags": ["attribute", "directive"]
}

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{
"compilerOptions": {
"target": "ES5",
"module": "commonjs",
"sourceMap": true,
"emitDecoratorMetadata": true,
"experimentalDecorators": true,
"removeComments": false,
"noImplicitAny": true,
"suppressImplicitAnyIndexErrors": true
}
}

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"intro": "A form creates a cohesive, effective, and compelling data entry experience. An Angular form coordinates a set of data-bound user controls, tracks changes, validates input, and presents errors."
},
"pipes": {
"title": "Pipes",
"intro": "Pipes transform displayed values within a template"
"dependency-injection": {
"title": "Dependency Injection",
"intro": "Angular's dependency injection system creates and delivers dependent services \"just-in-time\"."
},
"template-syntax": {
@ -34,15 +34,21 @@
"intro": "How to write templates that display data and consume user events with the help of data binding."
},
"dependency-injection": {
"title": "Dependency Injection",
"intro": "Angular's dependency injection system creates and delivers dependent services \"just-in-time\"."
"pipes": {
"title": "Pipes",
"intro": "Pipes transform displayed values within a template"
},
"attribute-directives": {
"title": "Attribute Directives",
"intro": "Attribute directives attach behavior to elements."
},
"hierarchical-dependency-injection": {
"title": "Hierarchical Injectors",
"intro": "Angular's hierarchical dependency injection system supports nested injectors in parallel with the component tree."
},
"glossary": {
"title": "Glossary",
"intro": "Brief definitions of the most important words in the Angular 2 vocabulary"

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include ../../../../_includes/_util-fns
:marked
An **Attribute** directive changes the appearance or behavior of a DOM element.
:marked
In this chapter we will
* write an attribute directive to change the background color
* apply the attribute directive to an element in a template
* respond to user-initiated events
* pass a value into the directive using data binding
[Live Example](/resources/live-examples/attribute-directives/ts/src/plnkr.html)
## Directives overview
There are three kinds of directives in Angular:
1. Components
1. Structural directives
1. Attribute directives
The *Component* is really a directive with a template.
It's the most common of the three directives and we write lots of them as we build our application.
The *Structural* directive changes the DOM layout by adding and removing DOM elements.
[NgFor](template-syntax.html#ng-for) and [NgIf](template-syntax.html#ng-if) are two familiar examples.
The *Attribute* directive changes the appearance or behavior of an element.
The built-in [NgStyle](template-syntax.html#ng-style) directive, for example,
can change several element styles at the same time.
We are going to write our own attribute directive to set an element's background color
when the user hovers over that element.
.l-sub-section
:marked
We don't need *any* directive to simply set the background color.
We can set it with the special [Style Binding](template-syntax.html#style-binding) like this:
code-example.
&lt;p [style.background]="'lime'">I am green with envy!&lt;/p>
<br>
:marked
That wouldn't be nearly as much fun as creating our own directive.
Besides, we're not just *setting* the color; we'll be *changing* the color
in response to a user action, a mouse hover.
.l-main-section
:marked
## Build a simple attribute directive
An attribute directive minimally requires building a controller class annotated with a
`Directive` decorator. The `Directive` decorator specifies the selector identifying
the attribute associated with the directive.
The controller class implements the desired directive behavior.
Let's build a small illustrative example together.
### Setup
Create a new project folder (`attribute-directives`) and follow the steps in the [QuickStart](../quickstart.html).
As in the [tutorial](/docs/ts/latest/tutorial/), we'll rename `app.ts` to `app.component.ts`
and relocate the call to `bootstrap` to a separate `boot.ts` file.
+makeExample('attribute-directives/ts/src/app/boot.ts', null, 'app/boot.ts')
:marked
A clean `app.component.ts` without bootstrapping is much easer to test.
Finally, we remember to update `index.html` to load `boot.ts`
code-example.
System.import('app/boot');
:marked
### Write the directive
Add a new file to the `app` folder called `highlight.directive.ts` and add the following code:
+makeExample('attribute-directives/ts/src/app/highlight.directive.1.ts', null, 'app/highlight.directive.ts')
:marked
We begin by importing some symbols from the Angular library.
We need the `Directive` symbol for the `@Directive` decorator.
We need symbols for the *Element Reference* and the *Renderer* service that
we will [inject](dependency-injection.html) into the directive's constructor.
We don't need `Input` now but we will need it later in the chapter.
Then we define the directive metadata in a configuration object passed
as an argument to the `@Directive` decorator function.
A `@Directive` decorator for an attribute directive requires a css selector to identify
the HTML in the template that is associated with our directive.
The [css selector for an attribute](https://developer.mozilla.org/en-US/docs/Web/CSS/Attribute_selectors)
is the attribute name in square brackets.
Our directive's selector is `[my-highlight]`.
Angular will locate all elements in the template that have an attribute named `my-highlight`.
.l-sub-section
:marked
### Why not call it "highlight"?
*highlight* is a nicer name than *my-highlight* and, technically, it would work if we called it that.
However, the good folks at Angular strongly prefer hyphenated directive selector names.
The HTML standards body will never name one of its attributes with a hyphen and there is
less risk of colliding with a third-party directive name when we give ours a prefix.
The `ng-` prefix belongs to Angular.
We need a prefix of our own, preferably short, and `my-` will do for now.
:marked
After the `@Component` metadata comes the directive's controller class which we are exporting
to make it accessible to other components.
The directive's controller class contains the logic for our directive.
Angular creates a new instance of the directive's controller class for
each matching element, injecting an *Element Reference* and
the *Renderer* service as arguments to our constructor.
We'll need them to set the element's background color.
Our code shows two ways to do that.
We could access the `nativeElement` property of the element reference
and set the element's background using the browser DOM API. We don't need
the `Renderer` for this technique. But we commented it out.
We chose the second way, the preferred way, that relies on the `Renderer` service
to set the element properties.
.l-sub-section
:marked
### Why prefer the Renderer?
Manipulating the DOM directly is a practice we should *avoid* because it chains us
to the browser DOM API.
The `Renderer` insulates our code from the browser's API.
That gives us options.
The rendering phase could be offloaded to a Web Worker for faster performance.
Our directive might work when we ran the application outside the browser,
perhaps on the server in a pre-render phase.
Server-side rendering can make our application load faster and
is often friendlier to Search Engine Optimizations (SEO).
:marked
.l-main-section
:marked
## Apply the attribute directive
The `AppComponent` will be the test harness for our `highlight` directive.
Let's give it a new template that
applies the directive as an attribute to a `span` element.
In Angular terms, the `<span>` element will be the attribute **host**.
We'll put the template in its own `app.component.html` file that looks like this:
+makeExample('attribute-directives/ts/src/app/app.component.1.html',null,'app/app.component.html')
:marked
A separate template file is clearly overkill for a 2-line template.
Hang in there; we're going to expand it later.
Meanwhile, we'll revise the `AppComponent` to reference this template.
+makeExample('attribute-directives/ts/src/app/app.component.ts',null,'app/app.component.ts')
:marked
We've added an `import` statement to fetch the 'Highlight' directive and
added that class to a `directives` array in the component metadata so that Angular
will recognize our directive when it encounters `my-highlight` in the template.
Angular would simply ignore the `my-highlight` attribute without it.
We run the app and see that our directive highlights the span text.
figure.image-display
img(src="/resources/images/devguide/attribute-directives/first-highlight.png" alt="First Highlight")
:marked
Let's recap what happened.
Angular found the `my-highlight` attribute on the `<span>` element. It created
an instance of the `Highlight` directive class,
injecting both a reference to the element and the `Renderer` service into the constructor.
The constructor told the `Renderer` to set the `<span>` element's background style to yellow.
.l-main-section
:marked
## Respond to user action
We are not satisfied to simply set an element color.
Our directive should set the color in response to a user action.
Specifically, we want to set the color when the user mouses over the element.
We'll need to
1. detect when the user mouses into and out of the element
1. respond to those actions by setting and clearing the highlight color.
Start with event detection.
We add a `host` property to the directive metadata and give it a configuration object
that specifies two mouse events and the directive methods to call when they are raised.
+makeExample('attribute-directives/ts/src/app/highlight.directive.2.ts','host')
:marked
.l-sub-section
:marked
The `host` property refers to the DOM element that hosts our attribute directive, the `<span>` in our case.
We could have attached an event listener to the native element (`el.nativeElement`) with
plain old JavaScript.
There are at least three problems with that approach:
1. We have to write the listeners correctly.
1. We must *detach* our listener when the directive is destroyed to avoid memory leaks.
1. We'd be talking to DOM API directly which, we learned, is something to avoid.
Let's roll with the `host` property.
:marked
Now we implement those two mouse event handlers:
+makeExample('attribute-directives/ts/src/app/highlight.directive.2.ts','mouse-methods')
:marked
Notice that they delegate to a helper method that calls the `Renderer` service
as we used to do in the constructor.
We no longer need the constructor body but
we still want the injected `ElementRef` and `Renderer` service.
We revise the constructor signature to capture the injectables in private variables
and clear the body.
+makeExample('attribute-directives/ts/src/app/highlight.directive.2.ts','ctor')
:marked
Here's the updated directive:
+makeExample('attribute-directives/ts/src/app/highlight.directive.2.ts',null, 'app/highlight.directive.ts')
:marked
We run the app and confirm that the background color appears as we move the mouse over the `span` and
disappears as we move out.
figure.image-display
img(src="/resources/images/devguide/attribute-directives/highlight-directive-anim.gif" alt="Second Highlight")
:marked
.l-main-section
:marked
## Configure the directive with binding
Currently the highlight color is hard-coded within the directive. That's inflexible.
We should set the highlight color externally with a binding like this:
+makeExample('attribute-directives/ts/src/app/app.component.html','span')
:marked
We'll extend our directive class with a bindable **input** `highlightColor` property and use it when we highlight text.
Here is the final version of the class:
+makeExample('attribute-directives/ts/src/app/highlight.directive.ts', 'class', 'app/highlight.directive.ts (class only)')
:marked
The new `highlightColor` property is called an "input" property because data flows from the binding expression into our directive.
Notice that we call the `@Input()` decorator function while defining the property.
+makeExample('attribute-directives/ts/src/app/highlight.directive.ts', 'color')
:marked
This `@Input` decorator adds metadata to the class that makes the `highlightColor` property available for property binding
under the `my-highlight` alias.
We must add this input metadata. Angular will give us an error if we try to bind
to a property without declaring it as an input.
.l-sub-section
:marked
The developer who uses our directive expects to bind to the attribute name, `my-highlight`.
The directive property name is `highlightColor`. That's a disconnect.
We can resolve the discrepancy by renaming the property to `myHighlight` and define it as follows:
+makeExample('attribute-directives/ts/src/app/highlight.directive.ts', 'highlight')
<br>
:marked
We don't like that property name.
We prefer, in this case, to **alias** the `highlightColor` property with the attribute name by
passing `my-highlight` into the `@Input` decorator:
+makeExample('attribute-directives/ts/src/app/highlight.directive.ts', 'color')
:marked
Now that we're getting the highlight color as an input, we modify the `onMouseEnter()` method to use
it instead of the hard-coded color name.
We also define a red default color as a fallback in case
the user neglects to bind with a color.
+makeExample('attribute-directives/ts/src/app/highlight.directive.ts', 'mouse-enter')
:marked
Now we'll update our `AppComponent` template to let
users pick the highlight color and bind their choice to our directive.
Here is the updated template:
+makeExample('attribute-directives/ts/src/app/app.component.html')
.l-sub-section
:marked
### Where is the templated *color* property?
The eagle-eyed may notice that the radio button click handlers in the template set a `color` property
and we are binding that `color` to the directive.
We should expect to find a `color` on the host `AppComponent`.
**We never defined a color property for the host *AppComponent***!
And yet this code works. Where is the template `color` value going?
Browser debugging reveals that Angular dynamically added a `color` property
to the runtime instance of the `AppComponent`.
This is *convenient* behavior but it is also *implicit* behavior that could be confusing.
While it's cool that this technique works, we recommend adding the `color` property to the `AppComponent`.
:marked
Here is our final app in action.
figure.image-display
img(src="/resources/images/devguide/attribute-directives/highlight-directive-final-anim.gif" alt="Final Highlight")
:marked
.l-main-section
:marked
## Summary
Now we know how to
- build a simple **attribute directive** to attach behavior to an HTML element,
- use that directive in a template,
- respond to **events** to change behavior based on an event,
- and use **binding** to pass a value to the attribute directive.
The final source:
+makeTabs(
`attribute-directives/ts/src/app/app.component.ts,
attribute-directives/ts/src/app/app.component.html,
attribute-directives/ts/src/app/highlight.directive.ts,
attribute-directives/ts/src/app/boot.ts,
attribute-directives/ts/src/index.html
`,
',,full',
`app.component.ts,
app.component.html,
highlight.directive.ts,
boot.ts,
index.html
`)

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@ -559,8 +559,8 @@ include ../../../../_includes/_util-fns
The Angular Dependency Injection is more capable than we've described.
We can learn more about its advanced features, beginning with its support for
a hierarchy of nested injectors in the next
[Dependency Injection chapter](./hierarchical-dependency-injection.html)
nested injectors, in the
[Hierarchical Dependency Injection](./hierarchical-dependency-injection.html) chapter.
.l-main-section
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