效果图：

redbook.gif

git链接：https://github.com/BelongsH/RedBook

大概介绍一下项目里面的一些知识点：

• 动态更改ViewPager的高度
• RecyclerView瀑布流的处理
• RecyclerView多type的处理

如何动态的去修改ViewPager的高度？

要动态的修改ViewPager的高度，首先需要知道ViewPager中每一个Item的高度。那么怎么确定高度呢？在开发中，一般服务端会把图片的宽度和高度通过api传给我们, 如果没有的话，我们也可以通过图片加载框架获取到图片本身的宽和高。

Paste_Image.png

假设这个时候，服务端传给我们这样的数据，我们就可以知道图片的宽和高。因为宽度是充满全屏不变的。然后我们拿图片的原始宽度/屏幕的宽度=缩放比率。通过这个缩放比率，就可以知道图片的高度。然后把它封装到一个数据结构中，方便使用。

    public class PictureSize {
        private int originalHeight;
        private int originalWidth;
        private float scale;
        private int scaleHeight;
        private int scaleWidth;


        public static PictureSize caculatePictureSize(int originalHeight, int originalWidth, int screenWidth) {
            PictureSize pictureSize = new PictureSize();
            pictureSize.originalHeight = originalHeight;
            pictureSize.originalWidth = originalWidth;
            pictureSize.scale = (screenWidth + 0f) / originalWidth;
            pictureSize.scaleHeight = (int) (originalHeight * pictureSize.scale);
            pictureSize.scaleWidth = screenWidth;
            return pictureSize;
        }  
    } 

这样的话，我们可以计算出ViewPage中的每一个item的高度。那么现在需要处理的就是滑动的距离和图片高度缩放的问题。首先我们需要获取到ViewPage的滑动比率（是指滑动距离相对整个屏幕的百分比）。通过setPageTransformer的方法就可以获取到一个position，这个position是相对View的一个的滑动比率。然后用这个滑动比率*item之间的高度差，就可以计算出滑动的高度值。

    holder1.vpHeadDelegate.setPageTransformer(true, new ViewPager.PageTransformer() {
                @Override
                public void transformPage(View page, float position) {
                    if (position > 0 && position <= 1) {
                        int badgePosition = (int) (page.getX() / screenWidth) - 1;
                        PictureSize offsetModel = mPictureSizes.get(String.valueOf(badgePosition + 1));
                        if (offsetModel == null) return;
                        PictureSize nowModel = mPictureSizes.get(String.valueOf(badgePosition));
                        float disHeight = (offsetModel.getScaleHeight() - nowModel.getScaleHeight()) * (1 - position);
                        LinearLayout.LayoutParams params = (LinearLayout.LayoutParams) holder1.vpHeadDelegate.getLayoutParams();
                        params.width = nowModel.getScaleWidth();
                        params.height = (int) (nowModel.getScaleHeight() + disHeight);
                        holder1.vpHeadDelegate.setLayoutParams(params);
                        holder1.vpHeadDelegate.requestLayout();
                    }
                }
            });

这样的话，我们就完成了，动态更改ViewPager的高度。

RecyclerView瀑布流的处理

使用RecyclerView来处理瀑布流的话，是非常easy的事情.通过

     RecyclerView.LayoutManager layoutManager = new StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL);
            rvMain.setLayoutManager(layoutManager);

然后动态的去计算每一个item的高度

     ViewHolder viewHolder = (ViewHolder) holder;
            NoteModel itemModel = (NoteModel) items.get(position);
            PictureModel model = itemModel.pictures.get(0);
            LinearLayout.LayoutParams layoutParams = (LinearLayout.LayoutParams) viewHolder.ivContentImage.getLayoutParams();
            float halfWidth = (ScreenUtils.getScreenWidth(holder.itemView.getContext()) - 60) / 2;
            layoutParams.width = (int) halfWidth;
            PictureSize pictureSize = PictureSize.caculatePictureSize(model.height, model.width, (int) halfWidth);
            layoutParams.height = pictureSize.getScaleHeight();
            viewHolder.ivContentImage.setLayoutParams(layoutParams);
            viewHolder.tvNoteDes.setText(itemModel.desc);
            viewHolder.tvNoteTitle.setText(itemModel.title);
            viewHolder.tvUserName.setText(itemModel.user.nickname);
            viewHolder.tvNoteTitle.setText(itemModel.title);
            StaggeredGridLayoutManager.LayoutParams params = (StaggeredGridLayoutManager.LayoutParams) viewHolder.itemView.getLayoutParams();
            params.setMargins(15, 15, 15, 15);
            holder.itemView.setLayoutParams(params);
            Glide.with(holder.itemView.getContext()).load(model.url).centerCrop().diskCacheStrategy(DiskCacheStrategy.ALL).into(viewHolder.ivContentImage);

需要注意的是，在StaggeredGridLayoutManager需要让item全屏的话，可以这样:

  HeadViewHolder headViewHolder = new HeadViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.item_note_head, parent, false));
        StaggeredGridLayoutManager.LayoutParams layoutParams = new StaggeredGridLayoutManager.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT);
        layoutParams.setFullSpan(true);
        headViewHolder.itemView.setLayoutParams(layoutParams);
        screenWidth = (ScreenUtils.getScreenWidth(parent.getContext()) + 0f);

RecyclerView多type的处理

在RecyclerView.Adapter 中处理多type的话，会让代码变得臃肿，而且不易协作开发。比如

public class NoteAdapter extends RecyclerView.Adapter {

  final int VIEW_TYPE_ACCESS_0 = 0;
  final int VIEW_TYPE_ACCESS_1 = 1;
  final int VIEW_TYPE_ACCESS_2 = 2;
  final int VIEW_TYPE_ACCESS_3 = 3;

  List<Accessory> items;

  @Override public int getItemViewType(int position) {
     Accessory accessory = items.get(postion);
     if (position==0){
       return VIEW_TYPE_ACCESS_0;
     } else if(position==1) {
       return VIEW_TYPE_ACCESS_1;
     }else if(position==2) {
       return VIEW_TYPE_ACCESS_2;
     }else  {
       return VIEW_TYPE_ACCESS_3;
     }
  }

  @Override public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    if (VIEW_TYPE_ACCESS_0 == viewType){
      return new ViewHolder1(inflater.inflate(R.layout.item_1, parent));
    } else if(VIEW_TYPE_ACCESS_1==viewType) {
      return new ViewHolder2 (inflater.inflate(R.layout.ietm_2,parent)):
    }else if(VIEW_TYPE_ACCESS_2==viewType) {
      return new ViewHolder2 (inflater.inflate(R.layout.ietm_3,parent)):
    }else if(VIEW_TYPE_ACCESS_3==viewType) {
      return new ViewHolder2 (inflater.inflate(R.layout.ietm_4,parent)):
    }
  }
}

这样的话，所有的代码都在一个类中，代码会变得越来越臃肿。不易维护。而且协作开发问题也是非常的大，（多人操作同一文件）我们可以通过给Adapter设置一个代理，由它来完成所需要的操作。下面是对这个代理的抽象

   public abstract class AdapterDelegate<T> {
      protected abstract boolean isForViewType(@NonNull T items, int position);
      @NonNull abstract protected RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent);
      protected abstract void onBindViewHolder(@NonNull T items, int position,
          @NonNull RecyclerView.ViewHolder holder, @NonNull List<Object> payloads);
      protected void onViewRecycled(@NonNull RecyclerView.ViewHolder viewHolder) {}
      protected boolean onFailedToRecycleView(@NonNull RecyclerView.ViewHolder holder) {
        return false;
      }
      protected void onViewAttachedToWindow(@NonNull RecyclerView.ViewHolder holder) {}
      protected void onViewDetachedFromWindow(RecyclerView.ViewHolder holder) {}
    }

然后我们将自己的核心代理继承并实现这个基类，在isForViewType中来判断当前的position是不是我们需要处理的Item，然后在onCreateViewHolder>onBindViewHolder。

    public class ContentDelegate extends AdapterDelegate<List<HomeModel>> {


        @Override
        protected boolean isForViewType(@NonNull List<HomeModel> items, int position) {
            return items.get(position) instanceof NoteModel;
        }

        @NonNull
        @Override
        protected RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent) {
            View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_note_notes, parent, false);
            return new ViewHolder(view);
        }

        @Override
        protected void onBindViewHolder(@NonNull List<HomeModel> items, int position, @NonNull RecyclerView.ViewHolder holder, @NonNull List<Object> payloads) {
            ViewHolder viewHolder = (ViewHolder) holder;
            NoteModel itemModel = (NoteModel) items.get(position);
            PictureModel model = itemModel.pictures.get(0);
            LinearLayout.LayoutParams layoutParams = (LinearLayout.LayoutParams) viewHolder.ivContentImage.getLayoutParams();
            float halfWidth = (ScreenUtils.getScreenWidth(holder.itemView.getContext()) - 60) / 2;
            layoutParams.width = (int) halfWidth;
            PictureSize pictureSize = PictureSize.caculatePictureSize(model.height, model.width, (int) halfWidth);
            layoutParams.height = pictureSize.getScaleHeight();
            viewHolder.ivContentImage.setLayoutParams(layoutParams);
            viewHolder.tvNoteDes.setText(itemModel.desc);
            viewHolder.tvNoteTitle.setText(itemModel.title);
            viewHolder.tvUserName.setText(itemModel.user.nickname);
            viewHolder.tvNoteTitle.setText(itemModel.title);
            StaggeredGridLayoutManager.LayoutParams params = (StaggeredGridLayoutManager.LayoutParams) viewHolder.itemView.getLayoutParams();
            params.setMargins(15, 15, 15, 15);
            holder.itemView.setLayoutParams(params);
            Glide.with(holder.itemView.getContext()).load(model.url).centerCrop().diskCacheStrategy(DiskCacheStrategy.ALL).into(viewHolder.ivContentImage);
            Glide.with(viewHolder.ivContentImage.getContext()).load(itemModel.user.images).override(pictureSize.getScaleWidth(), pictureSize.getScaleHeight()).diskCacheStrategy(DiskCacheStrategy.ALL).bitmapTransform(new CropCircleTransformation(viewHolder.ivUserHead.getContext())).placeholder(R.drawable.ic_default_head).into(viewHolder.ivUserHead);
        }
    }

而这些核心代理会在AdapterDelegatesManager中被添加到AdapterDelegatesManager中，进行判断当前的逻辑，所以你需要做的就是继承AbsDelegationAdapter，然后，将自己的多type添加进去即可。

    public class HomeAdapter extends AbsDelegationAdapter<List<HomeModel>> {
        private List<HomeModel> mDatas;
        public HomeAdapter(List<HomeModel> datas) {
            super();
            setItems(datas);
            this.mDatas = datas;
            this.delegatesManager.addDelegate(new HeadDelegate());
            this.delegatesManager.addDelegate(new ContentDelegate());
            this.delegatesManager.addDelegate(new CommentDelegate());
        }

        @Override
        public int getItemCount() {
            return mDatas.size();
        }
    }

关于多type的更多介绍:
http://hannesdorfmann.com/android/adapter-delegates
https://github.com/BelongsH/RedBook