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docs(Displaying Data): copy edits (#2435)

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Kapunahele Wong 2016-09-23 19:53:50 -04:00 committed by Kathy Walrath
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public/docs/ts/latest/guide/_data.json
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@ -17,7 +17,7 @@
"displaying-data": {
"title": "Displaying Data",
"intro": "Interpolation and other forms of property binding help us show app data in the UI.",
"intro": "Property binding helps show app data in the UI.",
"nextable": true,
"basics": true
},

175
public/docs/ts/latest/guide/displaying-data.jade
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@ -2,13 +2,12 @@ block includes
include ../_util-fns
- var _iterableUrl = 'https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols';
- var _boolean = 'truthy/falsey';
:marked
We typically display data in Angular by binding controls in an HTML template
to properties of an Angular component.
In this chapter, we'll create a component with a list of heroes. Each hero has a name.
We'll display the list of hero names and
:marked
You can display data by binding controls in an HTML template to properties of an Angular component.
In this page, you'll create a component with a list of heroes.
You'll display the list of hero names and
conditionally show a message below the list.
The final UI looks like this:
@ -17,42 +16,42 @@ figure.image-display
img(src="/resources/images/devguide/displaying-data/final.png" alt="Final UI")
:marked
# Table Of Contents
# Contents
* [Showing component properties with interpolation](#interpolation)
* [Showing !{_an} !{_array} property with NgFor](#ngFor)
* [Conditional display with NgIf](#ngIf)
* [Showing component properties with interpolation](#interpolation).
* [Showing !{_an} !{_array} property with NgFor](#ngFor).
* [Conditional display with NgIf](#ngIf).
.l-sub-section
:marked
The <live-example></live-example> demonstrates all of the syntax and code
snippets described in this chapter.
snippets described in this page.
.l-main-section#interpolation
:marked
## Showing component properties with interpolation
The easiest way to display a component property
is to bind the property name through interpolation.
With interpolation, we put the property name in the view template, enclosed in double curly braces: `{{myHero}}`.
With interpolation, you put the property name in the view template, enclosed in double curly braces: `{{myHero}}`.
Let's build a small illustrative example together.
Create a new project folder (<ngio-ex path="displaying-data"></ngio-ex>) and follow the steps in the [QuickStart](../quickstart.html).
To build an illustrative example, start by creating a new project folder called <ngio-ex path="displaying-data"></ngio-ex>
and following the steps in [QuickStart](../quickstart.html).
block quickstart-repo
include ../_quickstart_repo
:marked
Then modify the <ngio-ex path="app.component.ts"></ngio-ex> file by
Then modify the <ngio-ex path="app.component.ts"></ngio-ex> file by
changing the template and the body of the component.
When we're done, it should look like this:
When you're done, it should look like this:
+makeExample('app/app.component.1.ts')
:marked
We added two properties to the formerly empty component: `title` and `myHero`.
You added two properties to the formerly empty component: `title` and `myHero`.
Our revised template displays the two component properties using double curly brace
The revised template displays the two component properties using double curly brace
interpolation:
+makeExcerpt('app/app.component.1.ts', 'template', '')
@ -61,10 +60,9 @@ block quickstart-repo
.l-sub-section
:marked
The template is a multi-line string within ECMAScript 2015 backticks (<code>\`</code>).
The backtick (<code>\`</code>) &mdash; which is *not* the same character as a single
quote (`'`) &mdash; has many nice features. The feature we're exploiting here
is the ability to compose the string over several lines, which makes for
much more readable HTML.
The backtick (<code>\`</code>)&mdash;which is *not* the same character as a single
quote (`'`)&mdash;allows you to compose a string over several lines, which makes the
HTML more readable.
:marked
Angular automatically pulls the value of the `title` and `myHero` properties from the component and
@ -74,43 +72,42 @@ block quickstart-repo
.l-sub-section
:marked
More precisely, the redisplay occurs after some kind of asynchronous event related to
the view such as a keystroke, a timer completion, or an async `XHR` response.
We don't have those in this sample.
But then the properties aren't changing on their own either. For the moment we must operate on faith.
the view, such as a keystroke, a timer completion, or a response to an HTTP request.
:marked
Notice that we haven't called **new** to create an instance of the `AppComponent` class.
Angular is creating an instance for us. How?
Notice that you don't call **new** to create an instance of the `AppComponent` class.
Angular is creating an instance for you. How?
Notice the CSS `selector` in the `@Component` !{_decorator} that specifies an element named `my-app`.
Remember back in [QuickStart](../quickstart.html) that we added the `<my-app>` element to the body of our `index.html` file:
The CSS `selector` in the `@Component` !{_decorator} specifies an element named `my-app`.
Remember back in [QuickStart](../quickstart.html) that you added the `<my-app>`
element to the body of your `index.html` file:
+makeExcerpt('index.html', 'body')
:marked
When we bootstrap with the `AppComponent` class (in <ngio-ex path="main.ts"></ngio-ex>), Angular looks for a `<my-app>`
When you bootstrap with the `AppComponent` class (in <ngio-ex path="main.ts"></ngio-ex>), Angular looks for a `<my-app>`
in the `index.html`, finds it, instantiates an instance of `AppComponent`, and renders it
inside the `<my-app>` tag.
Try running the app. It should display the title and hero name:
Now run the app. It should display the title and hero name:
figure.image-display
img(src="/resources/images/devguide/displaying-data/title-and-hero.png" alt="Title and Hero")
+ifDocsFor('ts')
:marked
Let's review some of the choices we made and consider alternatives.
The next few sections review some of the coding choices in the app.
:marked
## Template inline or template file?
We can store our component's template in one of two places.
We can define it *inline* using the `template` property, as we do here.
Or we can define the template in a separate HTML file and link to it in
You can store your component's template in one of two places.
You can define it *inline* using the `template` property, or you can define
the template in a separate HTML file and link to it in
the component metadata using the `@Component` !{_decorator}'s `templateUrl` property.
The choice between inline and separate HTML is a matter of taste,
circumstances, and organization policy.
Here we're using inline HTML because the template is small, and the demo
Here the app uses inline HTML because the template is small and the demo
is simpler without the additional HTML file.
In either style, the template data bindings have the same access to the component's properties.
@ -119,49 +116,44 @@ figure.image-display
:marked
## Constructor or variable initialization?
We initialized our component properties using variable assignment.
This is a wonderfully concise and compact technique.
Although this example uses variable assignment to initialize the components, you can instead declare and initialize the properties using a constructor:
Some folks prefer to declare the properties and initialize them within a constructor like this:
+makeExcerpt('app/app-ctor.component.ts', 'class')
:marked
That's fine too. The choice is a matter of taste and organization policy.
We'll adopt the more terse "variable assignment" style in this chapter simply because
there will be less code to read.
This app uses more terse "variable assignment" style simply for brevity.
.l-main-section#ngFor
:marked
## Showing !{_an} !{_array} property with ***ngFor**
We want to display a list of heroes. We begin by adding !{_an} !{_array} of hero names to the component and redefine `myHero` to be the first name in the !{_array}.
To display a list of heroes, begin by adding !{_an} !{_array} of hero names to the component and redefine `myHero` to be the first name in the !{_array}.
+makeExcerpt('app/app.component.2.ts', 'class')
:marked
Now we use the Angular `ngFor` directive in the template to display
Now use the Angular `ngFor` directive in the template to display
each item in the `heroes` list.
+makeExcerpt('app/app.component.2.ts', 'template')
:marked
Our presentation is the familiar HTML unordered list with `<ul>` and `<li>` tags. Let's focus on the `<li>` tag.
This UI uses the HTML unordered list with `<ul>` and `<li>` tags. The `*ngFor`
in the `<li>` element is the Angular "repeater" directive.
It marks that `<li>` element (and its children) as the "repeater template":
+makeExcerpt('app/app.component.2.ts ()', 'li', '')
:marked
We added a somewhat mysterious `*ngFor` to the `<li>` element.
That's the Angular "repeater" directive.
Its presence on the `<li>` tag marks that `<li>` element (and its children) as the "repeater template".
.alert.is-important
:marked
Don't forget the leading asterisk (\*) in `*ngFor`. It is an essential part of the syntax.
Learn more about this and `ngFor` in the [Template Syntax](./template-syntax.html#ngFor) chapter.
For more information, see the [Template Syntax](./template-syntax.html#ngFor) page.
:marked
Notice the `hero` in the `ngFor` double-quoted instruction;
it is an example of a [template input variable](./template-syntax.html#ngForMicrosyntax).
it is an example of a template input variable. Read
more about template input variables in the [microsyntax](./template-syntax.html#ngForMicrosyntax) section of
the [Template Syntax](./template-syntax.html) page.
Angular duplicates the `<li>` for each item in the list, setting the `hero` variable
to the item (the hero) in the current iteration. Angular uses that variable as the
@ -169,9 +161,8 @@ figure.image-display
.l-sub-section
:marked
We happened to give `ngFor` !{_an} !{_array} to display.
In fact, `ngFor` can repeat items for any [iterable](!{_iterableUrl})
object.
In this case, `ngFor` is displaying !{_an} !{_array}, but `ngFor` can
repeat items for any [iterable](!{_iterableUrl}) object.
:marked
Now the heroes appear in an unordered list.
@ -182,25 +173,25 @@ figure.image-display
:marked
## Creating a class for the data
We are defining our data directly inside our component.
That's fine for a demo but certainly isn't a best practice. It's not even a good practice.
Although we won't do anything about that in this chapter, we'll make a mental note to fix this down the road.
The app's code defines the data directly inside the component, which isn't best practice.
In a simple demo, however, it's fine.
At the moment, we're binding to !{_an} !{_array} of strings. We do that occasionally in real applications, but
most of the time we're binding to more specialized objects.
At the moment, the binding is to !{_an} !{_array} of strings.
In real applications, most bindings are to more specialized objects.
Let's turn our !{_array} of hero names into !{_an} !{_array} of `Hero` objects. For that we'll need a `Hero` class.
To convert this binding to use specialized objects, turn the !{_array}
of hero names into !{_an} !{_array} of `Hero` objects. For that you'll need a `Hero` class.
Create a new file in the `!{_appDir}` folder called <ngio-ex path="hero.ts"></ngio-ex> with the following code:
+makeExcerpt('app/hero.ts')
block hero-class
:marked
We've defined a class with a constructor and two properties: `id` and `name`.
You've defined a class with a constructor and two properties: `id` and `name`.
It might not look like we have properties, but we do. We're taking
advantage of a TypeScript shortcut in our declaration of the constructor parameters.
It might not look like the class has properties, but it does.
The declaration of the constructor parameters takes advantage of a TypeScript shortcut.
Consider the first parameter:
@ -208,26 +199,28 @@ block hero-class
:marked
That brief syntax does a lot:
* Declares a constructor parameter and its type
* Declares a public property of the same name
* Initializes that property with the corresponding argument when we "new" an instance of the class
* Declares a constructor parameter and its type.
* Declares a public property of the same name.
* Initializes that property with the corresponding argument when creating an instance of the class.
.l-main-section
:marked
## Using the Hero class
Let's make the `heroes` property in our component return !{_an} !{_array} of these `Hero` objects.
The `heroes` property in the component can now use the `Hero` class to return !{_an} !{_array}
of `Hero` objects:
+makeExcerpt('app/app.component.3.ts', 'heroes')
:marked
We'll have to update the template.
Next, update the template.
At the moment it displays the hero's `id` and `name`.
Let's fix that so we display only the hero's `name` property.
Fix that to display only the hero's `name` property.
+makeExcerpt('app/app.component.3.ts', 'template')
:marked
Our display looks the same, but now we know much better what a hero really is.
The display looks the same, but the code is clearer.
.l-main-section#ngIf
:marked
@ -235,29 +228,31 @@ block hero-class
Sometimes an app needs to display a view or a portion of a view only under specific circumstances.
In our example, we'd like to display a message if we have a large number of heroes, say, more than 3.
Let's change the example to display a message if there are more than three heroes.
The Angular `ngIf` directive inserts or removes an element based on a !{_boolean} condition.
We can see it in action by adding the following paragraph at the bottom of the template:
To see it in action, add the following paragraph at the bottom of the template:
+makeExcerpt('app/app.component.ts', 'message')
.alert.is-important
:marked
Don't forget the leading asterisk (\*) in `*ngIf`. It is an essential part of the syntax.
Learn more about this and `ngIf` in the [Template Syntax](./template-syntax.html#ngIf) chapter.
Read more about `ngIf` and `*` in the [ngIf section](./template-syntax.html#ngIf) of the [Template Syntax](./template-syntax.html) page.
:marked
The [template expression](./template-syntax.html#template-expressions) inside the double quotes
looks much like !{_Lang}, and it _is_ much like !{_Lang}.
When the component's list of heroes has more than 3 items, Angular adds the paragraph to the DOM and the message appears.
If there are 3 or fewer items, Angular omits the paragraph, so no message appears.
The template expression inside the double quotes,
`*ngIf="heros.length > 3"`, looks and behaves much like !{_Lang}.
When the component's list of heroes has more than three items, Angular adds the paragraph
to the DOM and the message appears. If there are three or fewer items, Angular omits the
paragraph, so no message appears. For more information,
see the [template expressions](./template-syntax.html#template-expressions) section of the
[Template Syntax](./template-syntax.html) page.
.alert.is-helpful
:marked
Angular isn't showing and hiding the message. It is adding and removing the paragraph element from the DOM.
That hardly matters here. But it would matter a great deal, from a performance perspective, if
we were conditionally including or excluding a big chunk of HTML with many data bindings.
Angular isn't showing and hiding the message. It is adding and removing the paragraph element from the DOM. That improves performance, especially in larger projects when conditionally including or excluding
big chunks of HTML with many data bindings.
:marked
Try it out. Because the !{_array} has four items, the message should appear.
@ -267,13 +262,13 @@ block hero-class
.l-main-section
:marked
## Summary
Now we know how to use:
- **Interpolation** with double curly braces to display a component property
- **ngFor** to display !{_an} !{_array} of items
- A !{_Lang} class to shape the **model data** for our component and display properties of that model
- **ngIf** to conditionally display a chunk of HTML based on a boolean expression
Now you know how to use:
- **Interpolation** with double curly braces to display a component property.
- **ngFor** to display !{_an} !{_array} of items.
- A !{_Lang} class to shape the **model data** for your component and display properties of that model.
- **ngIf** to conditionally display a chunk of HTML based on a boolean expression.
Here's our final code:
Here's the final code:
block final-code
+makeTabs(`displaying-data/ts/app/app.component.ts,
@ -281,4 +276,4 @@ block final-code
displaying-data/ts/app/app.module.ts,
displaying-data/ts/app/main.ts`,
'final,,,',
'app/app.component.ts, app/hero.ts, app.module.ts, main.ts')
'app/app.component.ts, app/hero.ts, app.module.ts, main.ts')