SampleContainerViewController.m

- (void)addViewController:(BOOL)animated
{
    CGRect destFinalFrame = self.destinationFrame;
    CGRect destInitialFrame = CGRectMake(CGRectGetMaxX(destFinalFrame),
                                         CGRectGetMinY(destFinalFrame),
                                         CGRectGetWidth(destFinalFrame),
                                         CGRectGetHeight(destFinalFrame));
    
    UIViewController *srcViewController = self.sourceViewController;
    UIViewController *destViewController = self.destinationViewController;
    
    // 1. addChildViewController:
    [srcViewController addChildViewController:destViewController];
    // 2. didMoveToParentViewController:
    [destViewController didMoveToParentViewController:srcViewController];
    // 3. viewの設定
    destViewController.view.frame = destInitialFrame;
    destViewController.view.autoresizingMask = UIViewAutoresizingNone;
    // 4. beginAppearanceTransition:animated:
    [srcViewController beginAppearanceTransition:NO animated:animated];
    [destViewController beginAppearanceTransition:YES animated:animated];
    // 5. addSubview:
    [srcViewController.view addSubview:destViewController.view];
    // 6. viewのアニメーション
    void (^before)() = ^{
        // any pre-animation process
    };
    void (^block)() = ^{
        // animation block
        destViewController.view.frame = destFinalFrame;
    };
    void (^finish)() = ^{
        // 7. endAppearanceTransition
        [srcViewController endAppearanceTransition];
        [destViewController endAppearanceTransition];
    };
    if (animated) {
        before();
        [[UIApplication sharedApplication] beginIgnoringInteractionEvents];
        [UIView animateWithDuration:0.3 delay:0 options:UIViewAnimationOptionCurveEaseOut animations:block completion:^(BOOL finished) {
            [[UIApplication sharedApplication] endIgnoringInteractionEvents];
            finish();
        }];
    } else {
        before();
        block();
        finish();
    }
}