屬性型指令
Attribute directives
使用屬性型指令,可以更改 DOM 元素和 Angular 元件的外觀或行為。
With attribute directives, you can change the appearance or behavior of DOM elements and Angular components.
有關包含本指南中程式碼片段的有效示例,請參見
See the
建立屬性型指令
Building an attribute directive
本節將引導你建立“突出顯示”指令,該指令會將宿主元素的背景色設定為黃色。
This section walks you through creating a highlight directive that sets the background color of the host element to yellow.
要建立指令,請使用 CLI 命令
ng generate directive
。To create a directive, use the CLI command
ng generate directive
.ng generate directive highlight
CLI 建立
src/app/highlight.directive.ts
以及相應的測試檔案src/app/highlight.directive.spec.ts
,並在AppModule
中宣告此指令類別。The CLI creates
src/app/highlight.directive.ts
, a corresponding test filesrc/app/highlight.directive.spec.ts
, and declares the directive class in theAppModule
.CLI 產生預設的
src/app/highlight.directive.ts
,如下所示:The CLI generates the default
src/app/highlight.directive.ts
as follows:src/app/highlight.directive.ts import { Directive } from '@angular/core'; @Directive({ selector: '[appHighlight]' }) export class HighlightDirective { constructor() { } }
@Directive()
裝飾器的配置屬性會指定指令的 CSS 屬性選擇器[appHighlight]
。The
@Directive()
decorator's configuration property specifies the directive's CSS attribute selector,[appHighlight]
.從
@angular/core
匯入ElementRef
。ElementRef
的nativeElement
屬性會提供對宿主 DOM 元素的直接訪問許可權。Import
ElementRef
from@angular/core
.ElementRef
grants direct access to the host DOM element through itsnativeElement
property.在指令的
constructor()
中新增ElementRef
以注入對宿主 DOM 元素的參考,該元素就是appHighlight
的作用目標。Add
ElementRef
in the directive'sconstructor()
to inject a reference to the host DOM element, the element to which you applyappHighlight
.向
HighlightDirective
類別中新增邏輯,將背景設定為黃色Add logic to the
HighlightDirective
class that sets the background to yellow.src/app/highlight.directive.ts import { Directive, ElementRef } from '@angular/core'; @Directive({ selector: '[appHighlight]' }) export class HighlightDirective { constructor(el: ElementRef) { el.nativeElement.style.backgroundColor = 'yellow'; } }
指令不支援名稱空間。
Directives do not support namespaces.
<p app:Highlight>This is invalid</p>
應用屬性型指令
Applying an attribute directive
要使用
HighlightDirective
,請將<p>
元素新增到 HTML 範本中,並以偽指令作為屬性。To use the
HighlightDirective
, add a<p>
element to the HTML template with the directive as an attribute.src/app/app.component.html <p appHighlight>Highlight me!</p>
Angualr 會建立 HighlightDirective
類別的實例,並將 <p>
元素的參考注入到該指令的建構函式中,它會將 <p>
元素的背景樣式設定為黃色。
Angular creates an instance of the HighlightDirective
class and injects a reference to the <p>
element into the directive's constructor, which sets the <p>
element's background style to yellow.
處理使用者事件
Handling user events
本節會展示如何檢測使用者何時將滑鼠移入或移出元素以及如何透過設定或清除突出顯示顏色來進行響應。
This section shows you how to detect when a user mouses into or out of the element and to respond by setting or clearing the highlight color.
從 '@angular/core' 匯入
HostListener
Import
HostListener
from '@angular/core'.src/app/highlight.directive.ts (imports) import { Directive, ElementRef, HostListener } from '@angular/core';
新增兩個事件處理程式,它們會在滑鼠進入或離開時做出響應,每個事件處理程式都帶有
@HostListener()
裝飾器。Add two event handlers that respond when the mouse enters or leaves, each with the
@HostListener()
decorator.src/app/highlight.directive.ts (mouse-methods) @HostListener('mouseenter') onMouseEnter() { this.highlight('yellow'); } @HostListener('mouseleave') onMouseLeave() { this.highlight(''); } private highlight(color: string) { this.el.nativeElement.style.backgroundColor = color; }
使用
@HostListener()
裝飾器,你可以訂閱本屬性型指令宿主 DOM 元素上的事件(在本例中是<p>
)。With the
@HostListener()
decorator, you can subscribe to events of the DOM element that hosts an attribute directive, the<p>
in this case.處理程式會委託給一個輔助方法
highlight()
,該方法會設定宿主 DOM 元素el
的顏色。The handlers delegate to a helper method,
highlight()
, that sets the color on the host DOM element,el
.
完整的指令如下:
The complete directive is as follows:
@Directive({
selector: '[appHighlight]'
})
export class HighlightDirective {
constructor(private el: ElementRef) { }
@HostListener('mouseenter') onMouseEnter() {
this.highlight('yellow');
}
@HostListener('mouseleave') onMouseLeave() {
this.highlight('');
}
private highlight(color: string) {
this.el.nativeElement.style.backgroundColor = color;
}
}
當指標懸停在 p 元素上時,背景顏色就會出現;而當指標移出時,背景顏色就會消失。
The background color appears when the pointer hovers over the paragraph element and disappears as the pointer moves out.

將值傳遞給屬性型指令
Passing values into an attribute directive
本節將引導你在應用 HighlightDirective
時設定突出顯示顏色。
This section walks you through setting the highlight color while applying the HighlightDirective
.
在
highlight.directive.ts
中,從@angular/core
匯入Input
。In
highlight.directive.ts
, importInput
from@angular/core
.src/app/highlight.directive.ts (imports) import { Directive, ElementRef, HostListener, Input } from '@angular/core';
新增一個
appHighlight
的@Input()
屬性。Add an
appHighlight
@Input()
property.src/app/highlight.directive.ts @Input() appHighlight = '';
@Input()
裝飾器會將元資料新增到此類別,以便讓該指令的appHighlight
屬性可用於繫結。The
@Input()
decorator adds metadata to the class that makes the directive'sappHighlight
property available for binding.在
app.component.ts
,將color
屬性新增到AppComponent
。In
app.component.ts
, add acolor
property to theAppComponent
.src/app/app.component.ts (class) export class AppComponent { color = 'yellow'; }
要同時應用指令和顏色,請透過
appHighlight
指令選擇器使用屬性繫結,將其設定為color
。To simultaneously apply the directive and the color, use property binding with the
appHighlight
directive selector, setting it equal tocolor
.src/app/app.component.html (color) <p [appHighlight]="color">Highlight me!</p>
[appHighlight]
屬性繫結執行兩項任務:The
[appHighlight]
attribute binding performs two tasks:將突出顯示指令應用於
<p>
元素applies the highlighting directive to the
<p>
element透過屬性繫結設定指令的突出顯示顏色
sets the directive's highlight color with a property binding
透過使用者輸入來設定值
Setting the value with user input
本節指導你新增單選按鈕,將你選擇的顏色繫結到 appHighlight
指令。
This section guides you through adding radio buttons to bind your color choice to the appHighlight
directive.
將標記新增到
app.component.html
以選擇顏色,如下所示:Add markup to
app.component.html
for choosing a color as follows:src/app/app.component.html (v2) <h1>My First Attribute Directive</h1> <h2>Pick a highlight color</h2> <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> <p [appHighlight]="color">Highlight me!</p>
修改
AppComponent.color
,使其沒有初始值。Revise the
AppComponent.color
so that it has no initial value.src/app/app.component.ts (class) export class AppComponent { color = ''; }
啟動本應用的開發伺服器,以驗證使用者可以透過單選按鈕選擇顏色。
Serve your application to verify that the user can choose the color with the radio buttons.
繫結到第二個屬性
Binding to a second property
本節將指導你配置應用程式,以便開發人員可以設定預設顏色。
This section guides you through configuring your application so the developer can set the default color.
將第二個
Input()
屬性defaultColor
新增到HighlightDirective
。Add a second
Input()
property toHighlightDirective
calleddefaultColor
.src/app/highlight.directive.ts (defaultColor) @Input() defaultColor = '';
修改指令的
onMouseEnter
,使其首先嚐試使用highlightColor
進行突出顯示,然後嘗試defaultColor
,如果兩個屬性都undefined
,則變回red
。Revise the directive's
onMouseEnter
so that it first tries to highlight with thehighlightColor
, then with thedefaultColor
, and falls back tored
if both properties areundefined
.src/app/highlight.directive.ts (mouse-enter) @HostListener('mouseenter') onMouseEnter() { this.highlight(this.highlightColor || this.defaultColor || 'red'); }
若要繫結到
AppComponent.color
並回退為預設顏色“紫羅蘭(violet)”,請新增以下 HTML。在這裡,defaultColor
繫結沒有使用方括號[]
,因為它是靜態的。To bind to the
AppComponent.color
and fall back to "violet" as the default color, add the following HTML. In this case, thedefaultColor
binding doesn't use square brackets,[]
, because it is static.src/app/app.component.html (defaultColor) <p [appHighlight]="color" defaultColor="violet"> Highlight me too! </p>
與元件一樣,你可以將指令的多個屬性繫結新增到宿主元素上。
As with components, you can add multiple directive property bindings to a host element.
如果沒有預設顏色(defaultColor)繫結,則預設為紅色。當用戶選擇一種顏色時,所選的顏色將成為突出顯示的顏色。
The default color is red if there is no default color binding. When the user chooses a color the selected color becomes the active highlight color.

透過 NgNonBindable
停用 Angular 處理過程
Deactivating Angular processing with NgNonBindable
要防止在瀏覽器中進行表示式求值,請將 ngNonBindable
新增到宿主元素。ngNonBindable
會停用範本中的插值、指令和繫結。
To prevent expression evaluation in the browser, add ngNonBindable
to the host element. ngNonBindable
deactivates interpolation, directives, and binding in templates.
在下面的示例中,表示式 {{ 1 + 1 }}
的渲染方式會和在程式碼編輯器的一樣,而不會顯示 2
。
In the following example, the expression {{ 1 + 1 }}
renders just as it does in your code editor, and does not display 2
.
<p>Use ngNonBindable to stop evaluation.</p>
<p ngNonBindable>This should not evaluate: {{ 1 + 1 }}</p>
將 ngNonBindable
應用於元素將停止對該元素的子元素的繫結。但是,ngNonBindable
仍然允許指令在應用 ngNonBindable
的元素上工作。在以下示例中,appHighlight
指令仍處於活躍狀態,但 Angular 不會對表示式 {{ 1 + 1 }}
求值。
Applying ngNonBindable
to an element stops binding for that element's child elements. However, ngNonBindable
still allows directives to work on the element where you apply ngNonBindable
. In the following example, the appHighlight
directive is still active but Angular does not evaluate the expression {{ 1 + 1 }}
.
<h3>ngNonBindable with a directive</h3>
<div ngNonBindable [appHighlight]="'yellow'">This should not evaluate: {{ 1 +1 }}, but will highlight yellow.
</div>
如果將 ngNonBindable
應用於父元素,則 Angular 會禁用該元素的子元素的任何插值和繫結,例如屬性繫結或事件繫結。
If you apply ngNonBindable
to a parent element, Angular disables interpolation and binding of any sort, such as property binding or event binding, for the element's children.