如何在初始化适配器时按顺序为RecyclerView项设置动画(按顺序)？

Question

我正在努力实现的目标

我想在线性垂直RecyclerView中按顺序显示项目.我希望第一个项目出现,然后是第二个项目,然后是第三个项目,依此类推.这是我想要完成的动画类型的一个例子.

---

我试过的

我已经尝试了这个问题中提供的方法:如何在RecyclerView项目出现时为其设置动画

但是,这并不是我想要完成的.这会导致RecyclerView中的所有项目一次出现,而不是一次出现一次.

---

我的代码

public class ParentCommentsAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

    private int lastPosition = -1;

    //constructor and other code not shown...

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder viewHolder, int position) {
        switch (viewHolder.getItemViewType()) {
            case OP:
                OPViewHolder ovh = (OPViewHolder) viewHolder;
                configureOPViewHolder(ovh, position);
                setAnimation(ovh.getContainer(), position);
                break;
            case COMMENT:
                CommentViewHolder cvh = (CommentViewHolder) viewHolder;
                configureCommentViewHolder(cvh, position);
                setAnimation(cvh.getContainer(), position);
                break;
            default:
                RecyclerViewSimpleTextViewHolder vh = (RecyclerViewSimpleTextViewHolder) viewHolder;
                configureDefaultViewHolder(vh, position);
                break;
        }

    }

    @Override
    public void onViewDetachedFromWindow(final RecyclerView.ViewHolder viewHolder)
    {

        switch (viewHolder.getItemViewType()) {
            case OP:
                ((OPViewHolder)viewHolder).clearAnimation();
                break;
            case COMMENT:
                ((CommentViewHolder)viewHolder).clearAnimation();
                break;
            default:
                break;
        }
    }

    private void configureDefaultViewHolder(RecyclerViewSimpleTextViewHolder vh, int position) {
        //code...
    }

    private void configureOPViewHolder(OPViewHolder vh1, int position) {
        //code...
    }

    private void configureCommentViewHolder(CommentViewHolder vh2, int position) {
        //code...
    }

    private void setAnimation(View viewToAnimate, int position)
    {
        // If the bound view wasn't previously displayed on screen, it's animated
        if (position > lastPosition)
        {
            Animation animation = AnimationUtils.loadAnimation(context, R.anim.fade_in);
            viewToAnimate.startAnimation(animation);
            lastPosition = position;
        }
    }

}

Answer 1

打电话后,setAdapter您可以运行以下内容:

recyclerView.getViewTreeObserver().addOnPreDrawListener(
        new ViewTreeObserver.OnPreDrawListener() {

            @Override
            public boolean onPreDraw() {
                recyclerView.getViewTreeObserver().removeOnPreDrawListener(this);

                for (int i = 0; i < recyclerView.getChildCount(); i++) {
                    View v = recyclerView.getChildAt(i);
                    v.setAlpha(0.0f);
                    v.animate().alpha(1.0f)
                            .setDuration(300)
                            .setStartDelay(i * 50)
                            .start();
                }

                return true;
            }
        });

示例显示了简单的alpha动画,但您可以在循环中运行所需的内容并调整插值器,持续时间和启动延迟.

Answer 2

我决定使用与Niko之前建议的不同的方法.他的方法效果很好而且很容易,但是在添加和删除项目时会导致一些错误的动画(这里可以看到).

所以我决定尝试不同的方法并使用布局动画控制器.这是我用来获得相同结果的代码.

public void initialRVAnimation() {

    AnimationSet set = new AnimationSet(true);

    // Fade in animation
    Animation fadeIn = new AlphaAnimation(0.0f, 1.0f);
    fadeIn.setDuration(400);
    fadeIn.setFillAfter(true);
    set.addAnimation(fadeIn);

    // Slide up animation from bottom of screen
    Animation slideUp = new TranslateAnimation(0, 0, Utils.getScreenHeight(this), 0);
    slideUp.setInterpolator(new DecelerateInterpolator(4.f));
    slideUp.setDuration(400);
    set.addAnimation(slideUp);

    // Set up the animation controller              (second parameter is the delay)
    LayoutAnimationController controller = new LayoutAnimationController(set, 0.2f);
    rv.setLayoutAnimation(controller);

    // Set the adapter
    adapter = new ItemAdapter(data, this);
    recyclerView.setAdapter(adapter);
}