适配器初始化时(按顺序)如何为RecyclerView项目设置动画? [英] How to animate RecyclerView items when adapter is initialized (in order)?

问题描述

我要完成的任务

我想使线性垂直RecyclerView中的项目按顺序显示.我要显示第一个项目，然后显示第二个项目，然后显示第三个项目，依此类推.这是我要完成的动画类型的示例.

I want to make items in a linear vertical RecyclerView appear in order. I want the 1st item to appear, then the 2nd, then the 3rd and so on. Here is an example of the type of animation I'm trying to accomplish.

我尝试过的事情

我尝试了此问题中提供的方法:如何进行动画处理RecyclerView物品出现时

I have tried the methods provided in this question: How to animate RecyclerView items when they appear

但是，这并不是我要完成的任务.这将导致RecyclerView中的所有项目一次出现，而不是一次出现.

However, this is not quite what I'm trying to accomplish. This causes all the items in the RecyclerView to appear at once, rather than one at a time.

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;
        }
    }

}

推荐答案

调用 setAdapter 后，您可以运行以下命令:

After you call setAdapter you can run following:

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，但是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.

Example shows simple alpha animation, but you can run what you want in the loop and adjust interpolator, duration and start delay.

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