Method _computePositionAnimationState

src/material/tabs/tab-body.ts:284–309

Computes the position state that will be used for the tab-body animation trigger.

(dir: Direction = this._getLayoutDirection())

  /** Computes the position state that will be used for the tab-body animation trigger. */
  private _computePositionAnimationState(dir: Direction = this._getLayoutDirection()) {
    this._previousPosition = this._position;

    if (this._positionIndex < 0) {
      this._position = dir == 'ltr' ? 'left' : 'right';
    } else if (this._positionIndex > 0) {
      this._position = dir == 'ltr' ? 'right' : 'left';
    } else {
      this._position = 'center';
    }

    if (this._animationsDisabled()) {
      this._simulateTransitionEvents();
    } else if (
      this._initialized &&
      (this._position === 'center' || this._previousPosition === 'center')
    ) {
      // The transition events are load-bearing and in some cases they might not fire (e.g.
      // tests setting `* {transition: none}` to disable animations). This timeout will simulate
      // them if a transition doesn't start within a certain amount of time.
      clearTimeout(this._fallbackTimer);
      this._fallbackTimer = this._ngZone.runOutsideAngular(() =>
        setTimeout(() => this._simulateTransitionEvents(), 100),
      );
    }
  }

  /** Simulates the body's transition events in an environment where they might not fire. */
  private _simulateTransitionEvents() {