文字方向 Bidirectionality

bidi 包为组件提供了一个通用的体系，来获取和响应该应用的 LTR（从左到右）/RTL（从右到左）布局方向的变化。

The bidi package provides a common system for components to get and respond to change in the application's LTR/RTL layout direction.

link 方向性

link Directionality

当包含 CDK 的 BidiModule 时，组件中就可以注入 Directionality 来获取当前的文本方向了（RTL 或者 LTR）;

When including the CDK's BidiModule, components can inject Directionality to get the current text direction (RTL or LTR);

link 例子

link Example

@Component({ ... }) 
export class MyWidget implements OnDestroy {

  /** Whether the widget is in RTL mode or not. */
  private isRtl: boolean;

  /** Subscription to the Directionality change EventEmitter. */
  private _dirChangeSubscription = Subscription.EMPTY;  

  constructor(dir: Directionality) {
    this.isRtl = dir.value === 'rtl';

    this._dirChangeSubscription = dir.change.subscribe(() => {
      this.flipDirection();
    });
  }

  ngOnDestroy() {
    this._dirChangeSubscription.unsubscribe();
  }
}  

link Dir 指令

link The Dir directive

BidiModule 还包含一个指令，用来匹配所有带 dir 属性的元素。该指令与 Directionality 具有相同的 API，并将自身作为 Directionality 的服务提供者。这样一来，任何注入了 Directionality 的组件都会得到关于最近祖先的布局方向上下文。

The BidiModule also includes a directive that matches any elements with a dir attribute. This directive has the same API as Directionality and provides itself as Directionality. By doing this, any component that injects Directionality will get the closest ancestor layout direction context.