Github学习之RecyclerView实现View滑动折叠效果

今天在Github上看了一篇通过RecyclerView实现喵街首页View滑动折叠效果，感觉博主很厉害，就记下学习之。

效果图

实现：

结构图：

添加依赖：

dependencies {
    compile fileTree(include: ['*.jar'], dir: 'libs')
    testCompile 'junit:junit:4.12'
    compile 'com.android.support:appcompat-v7:23.1.1'
    compile 'com.android.support:recyclerview-v7:23.1.1'
    compile 'com.github.bumptech.glide:glide:3.6.1'
}

主体由recyclerview+Glide实现。

由于需要动态设置item高度，透明度，字体大小

 item_max_height = (int) getResources().getDimension(R.dimen.item_max_height);
        item_normal_height = (int) getResources().getDimension(R.dimen.item_normal_height);
        item_normal_font_size = getResources().getDimension(R.dimen.item_normal_font_size);
        item_max_font_size = getResources().getDimension(R.dimen.item_max_font_size);
        item_normal_alpha = getResources().getFraction(R.fraction.item_normal_mask_alpha, 1, 1);
        item_max_alpha = getResources().getFraction(R.fraction.item_max_mask_alpha, 1, 1);

        font_size_d = item_max_font_size - item_normal_font_size;
        alpha_d = item_max_alpha - item_normal_alpha;

这里作者定义了分别定义了最大高度，正常高度，最大字体，正常字体，最大透明度值，正常透明度值。

MyAdapter myAdapter = new MyAdapter(this, walls);

利用MyAdapter传递数据，并显示。

HeaderAndFooterRecyclerViewAdapter headerAndFooterRecyclerViewAdapter = new HeaderAndFooterRecyclerViewAdapter(myAdapter);
        recyclerView.setAdapter(headerAndFooterRecyclerViewAdapter);
        View moreView = getLayoutInflater().inflate(R.layout.footer_more, null);
        TextView more = (TextView) moreView.findViewById(R.id.more);
        more.getLayoutParams().height = DeviceUtils.getScreenHeight(this) -
                item_max_height;
        RecyclerViewUtils.setFooterView(recyclerView, moreView);

利用HeaderAndFooterRecyclerViewAdapter添加底部View，RecyclerViewUtils设置顶部或者底部view的工具类。

recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);
                LinearLayoutManager linearLayoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();
                RecyclerView.ViewHolder firstViewHolder = recyclerView
                        .findViewHolderForLayoutPosition(linearLayoutManager.findFirstVisibleItemPosition());
                RecyclerView.ViewHolder secOndViewHolder= recyclerView
                        .findViewHolderForLayoutPosition(linearLayoutManager.findFirstCompletelyVisibleItemPosition());
                RecyclerView.ViewHolder threeViewHolder = recyclerView
                        .findViewHolderForLayoutPosition(linearLayoutManager.findFirstCompletelyVisibleItemPosition() + 1);
                RecyclerView.ViewHolder lastViewHolder = recyclerView
                        .findViewHolderForLayoutPosition(linearLayoutManager.findLastVisibleItemPosition());
                if (firstViewHolder != null && firstViewHolder instanceof MyAdapter.ViewHolder) {
                    MyAdapter.ViewHolder viewHolder = (MyAdapter.ViewHolder) firstViewHolder;
                    if (viewHolder.itemView.getLayoutParams().height - dy <= item_max_height
                            && viewHolder.itemView.getLayoutParams().height - dy >= item_normal_height) {
                        viewHolder.itemView.getLayoutParams().height = viewHolder.itemView.getLayoutParams().height - dy;
                        viewHolder.mark.setAlpha(viewHolder.mark.getAlpha() - dy * alpha_d / item_normal_height);
                        viewHolder.text.setTextSize(TypedValue.COMPLEX_UNIT_PX,
                                viewHolder.text.getTextSize() - dy * font_size_d / item_normal_height);
                        viewHolder.itemView.setLayoutParams(viewHolder.itemView.getLayoutParams());
                    }
                }
                if (secondViewHolder != null && secondViewHolder instanceof MyAdapter.ViewHolder) {
                    MyAdapter.ViewHolder viewHolder = (MyAdapter.ViewHolder) secondViewHolder;
                    if (viewHolder.itemView.getLayoutParams().height + dy <= item_max_height
                            && viewHolder.itemView.getLayoutParams().height + dy >= item_normal_height) {
                        viewHolder.itemView.getLayoutParams().height = viewHolder.itemView.getLayoutParams().height + dy;
                        viewHolder.mark.setAlpha(viewHolder.mark.getAlpha() + dy * alpha_d / item_normal_height);
                        viewHolder.text.setTextSize(TypedValue.COMPLEX_UNIT_PX,
                                viewHolder.text.getTextSize() + dy * font_size_d / item_normal_height);
                        viewHolder.itemView.setLayoutParams(viewHolder.itemView.getLayoutParams());
                    }
                }

                if (threeViewHolder != null && threeViewHolder instanceof MyAdapter.ViewHolder) {
                    MyAdapter.ViewHolder viewHolder = (MyAdapter.ViewHolder) threeViewHolder;
                    viewHolder.mark.setAlpha(item_normal_alpha);
                    viewHolder.text.setTextSize(TypedValue.COMPLEX_UNIT_PX, item_normal_font_size);
                    viewHolder.itemView.getLayoutParams().height = item_normal_height;
                    viewHolder.itemView.setLayoutParams(viewHolder.itemView.getLayoutParams());
                }
                if (lastViewHolder != null && lastViewHolder instanceof MyAdapter.ViewHolder) {
                    MyAdapter.ViewHolder viewHolder = (MyAdapter.ViewHolder) lastViewHolder;
                    viewHolder.mark.setAlpha(item_normal_alpha);
                    viewHolder.text.setTextSize(TypedValue.COMPLEX_UNIT_PX, item_normal_font_size);
                    viewHolder.itemView.getLayoutParams().height = item_normal_height;
                    viewHolder.itemView.setLayoutParams(viewHolder.itemView.getLayoutParams());
                }
            }
        });

这里利用recylerview的addOnScrollListener监听器，监听y轴滑动距离dy ，并根据dy动态设置字体大小，item高度。

github地址

https://github.com/dongjunkun/miaojiedemo