Method _trapFocus

src/cdk/dialog/dialog-container.ts:254–297

* Moves the focus inside the focus trap. When autoFocus is not set to 'dialog', if focus * cannot be moved then focus will go to the dialog container.

(options?: FocusOptions)

   * cannot be moved then focus will go to the dialog container.
   */
  protected _trapFocus(options?: FocusOptions) {
    if (this._isDestroyed) {
      return;
    }

    // If were to attempt to focus immediately, then the content of the dialog would not yet be
    // ready in instances where change detection has to run first. To deal with this, we simply
    // wait until after the next render.
    afterNextRender(
      () => {
        const element = this._elementRef.nativeElement;
        switch (this._config.autoFocus) {
          case false:
          case 'dialog':
            // Ensure that focus is on the dialog container. It's possible that a different
            // component tried to move focus while the open animation was running. See:
            // https://github.com/angular/components/issues/16215. Note that we only want to do this
            // if the focus isn't inside the dialog already, because it's possible that the consumer
            // turned off `autoFocus` in order to move focus themselves.
            if (!this._containsFocus()) {
              element.focus(options);
            }
            break;
          case true:
          case 'first-tabbable':
            const focusedSuccessfully = this._focusTrap?.focusInitialElement(options);
            // If we weren't able to find a focusable element in the dialog, then focus the dialog
            // container instead.
            if (!focusedSuccessfully) {
              this._focusDialogContainer(options);
            }
            break;
          case 'first-heading':
            this._focusByCssSelector('h1, h2, h3, h4, h5, h6, [role="heading"]', options);
            break;
          default:
            this._focusByCssSelector(this._config.autoFocus!, options);
            break;
        }
        (this._focusTrapped as Subject<void>).next();
      },
      {injector: this._injector},
    );
  }

  /** Restores focus to the element that was focused before the dialog opened. */
  private _restoreFocus() {