Method transition

core/src/components/nav/nav.tsx:867–923

(
    enteringView: ViewController,
    leavingView: ViewController | undefined,
    ti: TransitionInstruction
  )

  }

  private async transition(
    enteringView: ViewController,
    leavingView: ViewController | undefined,
    ti: TransitionInstruction
  ): Promise<NavResult> {
    // we should animate (duration > 0) if the pushed page is not the first one (startup)
    // or if it is a portal (modal, actionsheet, etc.)
    const opts = ti.opts!;

    const progressCallback = opts.progressAnimation
      ? (ani: Animation | undefined) => {
          /**
           * Because this progress callback is called asynchronously
           * it is possible for the gesture to start and end before
           * the animation is ever set. In that scenario, we should
           * immediately call progressEnd so that the transition promise
           * resolves and the gesture does not get locked up.
           */
          if (ani !== undefined && !this.gestureOrAnimationInProgress) {
            this.gestureOrAnimationInProgress = true;
            ani.onFinish(
              () => {
                this.gestureOrAnimationInProgress = false;
              },
              { oneTimeCallback: true }
            );

            /**
             * Playing animation to beginning
             * with a duration of 0 prevents
             * any flickering when the animation
             * is later cleaned up.
             */
            ani.progressEnd(0, 0, 0);
          } else {
            this.sbAni = ani;
          }
        }
      : undefined;
    const mode = getIonMode(this);
    const enteringEl = enteringView.element!;
    // eslint-disable-next-line @typescript-eslint/prefer-optional-chain
    const leavingEl = leavingView && leavingView.element!;
    const animationOpts: TransitionOptions = {
      mode,
      showGoBack: this.canGoBackSync(enteringView),
      baseEl: this.el,
      progressCallback,
      animated: this.animated && config.getBoolean('animated', true),
      enteringEl,
      leavingEl,
      ...opts,
      animationBuilder: opts.animationBuilder || this.animation || config.get('navAnimation'),
    };
    const { hasCompleted } = await transition(animationOpts);
    return this.transitionFinish(hasCompleted, enteringView, leavingView, opts);
  }