Component
一个装饰器，用于把某个类标记为 Angular 组件，并为它配置一些元数据，以决定该组件在运行期间该如何处理、实例化和使用。
Decorator that marks a class as an Angular component and provides configuration metadata that determines how the component should be processed, instantiated, and used at runtime.
| 选项 | 说明 |
|---|---|
changeDetection | 用于当前组件的变更检测策略。 The change-detection strategy to use for this component. |
viewProviders | 定义一组可注入对象，它们在视图的各个子节点中可用。参见例子。 Defines the set of injectable objects that are visible to its view DOM children. See example. |
moduleId | 包含该组件的那个模块的 ID。该组件必须能解析模板和样式表中使用的相对 URL。 SystemJS 在每个模块中都导出了 The module ID of the module that contains the component. The component must be able to resolve relative URLs for templates and styles. SystemJS exposes the |
templateUrl | Angular 组件模板文件的 URL。如果提供了它，就不要再用 The relative path or absolute URL of a template file for an Angular component. If provided, do not supply an inline template using |
template | Angular 组件的内联模板。如果提供了它，就不要再用 An inline template for an Angular component. If provided, do not supply a template file using |
styleUrls | 一个或多个 URL，指向包含本组件 CSS 样式表的文件。 One or more relative paths or absolute URLs for files containing CSS stylesheets to use in this component. |
styles | 本组件用到的一个或多个内联 CSS 样式。 One or more inline CSS stylesheets to use in this component. |
animations | 一个或多个动画 One or more animation |
encapsulation | 供模板和 CSS 样式使用的样式封装策略。取值为： An encapsulation policy for the template and CSS styles. One of: |
interpolation | 改写默认的插值表达式起止分界符（ Overrides the default encapsulation start and end delimiters ( |
entryComponents | 一个组件的集合，它应该和当前组件一起编译。对于这里列出的每个组件，Angular 都会创建一个 A set of components that should be compiled along with this component. For each component listed here, Angular creates a |
preserveWhitespaces | 为 True to preserve or false to remove potentially superfluous whitespace characters from the compiled template. Whitespace characters are those matching the |
继承自 Directive 装饰器
| 选项 | 说明 |
|---|---|
selector | 这个 CSS 选择器用于在模板中标记出该指令，并触发该指令的实例化。 The CSS selector that identifies this directive in a template and triggers instantiation of the directive. |
inputs | 列举某个指令的一组可供数据绑定的输入属性 Enumerates the set of data-bound input properties for a directive |
outputs | 列举一组可供事件绑定的输出属性。 Enumerates the set of event-bound output properties. |
providers | 一组依赖注入令牌，它允许 DI 系统为这个指令或组件提供依赖。 Configures the injector of this directive or component with a token that maps to a provider of a dependency. |
exportAs | 定义一个名字，用于在模板中把该指令赋值给一个变量。 Defines the name that can be used in the template to assign this directive to a variable. |
queries | 配置一些查询，它们将被注入到该指令中。 Configures the queries that will be injected into the directive. |
host | 使用一组键-值对，把类的属性映射到宿主元素的绑定（Property、Attribute 和事件）。 Maps class properties to host element bindings for properties, attributes, and events, using a set of key-value pairs. |
jit | 如果为 true，则该指令/组件将会被 AOT 编译器忽略，始终使用 JIT 编译。 If true, this directive/component will be skipped by the AOT compiler and so will always be compiled using JIT. |
说明
组件是 Angular 应用中最基本的 UI 构造块。Angular 应用中包含一棵组件树。
Components are the most basic UI building block of an Angular app. An Angular app contains a tree of Angular components.
Angular 的组件是指令的一个子集，它总是有一个与之关联的模板。 和其它指令不同，模板中的每个元素只能具有一个组件实例。
Angular components are a subset of directives, always associated with a template. Unlike other directives, only one component can be instantiated per an element in a template.
组件必须从属于某个 NgModule 才能被其它组件或应用使用。 要想让它成为某个 NgModule 中的一员，请把它列在 @NgModule 元数据的 declarations 字段中。
A component must belong to an NgModule in order for it to be available to another component or application. To make it a member of an NgModule, list it in the declarations field of the NgModule metadata.
注意，除了这些用来对指令进行配置的选项之外，你还可以通过实现生命周期钩子来控制组件的运行期行为。 要了解更多，参见 生命周期钩子 章。
Note that, in addition to these options for configuring a directive, you can control a component's runtime behavior by implementing life-cycle hooks. For more information, see the Lifecycle Hooks guide.
使用说明
设置组件的输入属性
Setting component inputs
下免得例子创建了一个带有两个数据绑定属性的组件，它是通过 inputs 值来指定的。
The following example creates a component with two data-bound properties, specified by the inputs value.
@Component({
selector: 'app-bank-account',
inputs: ['bankName', 'id: account-id'],
template: `
Bank Name: {{ bankName }}
Account Id: {{ id }}
`
})
export class BankAccountComponent {
bankName: string|null = null;
id: string|null = null;
// this property is not bound, and won't be automatically updated by Angular
normalizedBankName: string|null = null;
}
@Component({
selector: 'app-my-input',
template: `
<app-bank-account
bankName="RBC"
account-id="4747">
</app-bank-account>
`
})
export class MyInputComponent {
}
设置组件的输出属性
Setting component outputs
下面的例子展示了两个事件发生器，它们定时发出事件。一个每隔一秒发出一个输出事件，另一个则隔五秒。
The following example shows two event emitters that emit on an interval. One emits an output every second, while the other emits every five seconds.
@Directive({selector: 'app-interval-dir', outputs: ['everySecond', 'fiveSecs: everyFiveSeconds']})
export class IntervalDirComponent {
everySecond = new EventEmitter<string>();
fiveSecs = new EventEmitter<string>();
constructor() {
setInterval(() => this.everySecond.emit('event'), 1000);
setInterval(() => this.fiveSecs.emit('event'), 5000);
}
}
@Component({
selector: 'app-my-output',
template: `
<app-interval-dir
(everySecond)="onEverySecond()"
(everyFiveSeconds)="onEveryFiveSeconds()">
</app-interval-dir>
`
})
export class MyOutputComponent {
onEverySecond() { console.log('second'); }
onEveryFiveSeconds() { console.log('five seconds'); }
}
使用视图提供商注入一个类
Injecting a class with a view provider
下面的例子示范了如何在组件元数据中使用视图提供商来把一个类注入到组件中：
The following simple example injects a class into a component using the view provider specified in component metadata:
class Greeter {
greet(name:string) {
return 'Hello ' + name + '!';
}
}
@Directive({
selector: 'needs-greeter'
})
class NeedsGreeter {
greeter:Greeter;
constructor(greeter:Greeter) {
this.greeter = greeter;
}
}
@Component({
selector: 'greet',
viewProviders: [
Greeter
],
template: `<needs-greeter></needs-greeter>`
})
class HelloWorld {
}
Preserving whitespace
Removing whitespace can greatly reduce AOT-generated code size and speed up view creation. As of Angular 6, the default for preserveWhitespaces is false (whitespace is removed). To change the default setting for all components in your application, set the preserveWhitespaces option of the AOT compiler.
By default, the AOT compiler removes whitespace characters as follows:
- Trims all whitespaces at the beginning and the end of a template.
- Removes whitespace-only text nodes. For example,
<button>Action 1</button> <button>Action 2</button>
becomes:
<button>Action 1</button><button>Action 2</button>
- Replaces a series of whitespace characters in text nodes with a single space. For example,
<span>\n some text\n</span>becomes<span> some text </span>. - Does NOT alter text nodes inside HTML tags such as
<pre>or<textarea>, where whitespace characters are significant.
Note that these transformations can influence DOM nodes layout, although impact should be minimal.
You can override the default behavior to preserve whitespace characters in certain fragments of a template. For example, you can exclude an entire DOM sub-tree by using the ngPreserveWhitespaces attribute:
<div ngPreserveWhitespaces>
whitespaces are preserved here
<span> and here </span>
</div>
You can force a single space to be preserved in a text node by using &ngsp;, which is replaced with a space character by Angular's template compiler:
<a>Spaces</a>&ngsp;<a>between</a>&ngsp;<a>links.</a>
<!-->compiled to be equivalent to:</>
<a>Spaces</a> <a>between</a> <a>links.</a>
Note that sequences of &ngsp; are still collapsed to just one space character when the preserveWhitespaces option is set to false.
<a>before</a>&ngsp;&ngsp;&ngsp;<a>after</a>
<!-->compiled to be equivalent to:</>
<a>Spaces</a> <a>between</a> <a>links.</a>
To preserve sequences of whitespace characters, use the ngPreserveWhitespaces attribute.
