recycleview 网格布局setSpanSizeLookup的使用

1.空白布局

        GridLayoutManager layoutManager=new GridLayoutManager(getContext(),3);
        binding.rlvGrade.setLayoutManager(layoutManager);
        binding.rlvGrade.setAdapter(adapter);

        //设置空白数据时，空白布局占据的spanCount
        layoutManager.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
            @Override
            public int getSpanSize(int position) {
                int viewType = adapter.getItemViewType(position);
                if(viewType == -1) {
                    return 3;
                }
                return 1;
            }


        });

package com.mbzj.ykt_student.adapter;

import android.content.Context;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.core.content.ContextCompat;
import androidx.recyclerview.widget.RecyclerView;

import com.mbzj.ykt_student.R;
import com.mbzj.ykt_student.bean.GradeBean;

import java.util.List;

/**
 * @author David
 * @description:
 * @date :2020/7/28 18:02
 */
public class UserMessageSelectClassAdapter extends RecyclerView.Adapter {

    private int TYPE_EMPTY=-1;
    private int TYPE_DATA=1;

    private Context context;
    private List list;
    private onClickListener listener;

    public UserMessageSelectClassAdapter(Context context, List list,onClickListener listener) {
        this.context = context;
        this.list = list;
        this.listener = listener;
    }

    @NonNull
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        if (viewType==TYPE_EMPTY){
            return new EmptyViewHolder(LayoutInflater.from(context).inflate(R.layout.rlv_select_class_empty_item,parent,false));
        }else {
            return new SelectClassViewHolder(LayoutInflater.from(context).inflate(R.layout.rlv_user_msg_select_class_item,parent,false));
        }
    }

    @Override
    public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {
        if (holder instanceof SelectClassViewHolder){
            onBindSelectClassViewHolder((SelectClassViewHolder) holder,position);
        }else if (holder instanceof EmptyViewHolder){
            onBindEmptyViewHolder((EmptyViewHolder) holder,position);
        }
//        int itemViewType = getItemViewType(position);
//        if (itemViewType==TYPE_EMPTY){
//            onBindEmptyViewHolder((EmptyViewHolder) holder,position);
//        }else {
//            onBindSelectClassViewHolder((SelectClassViewHolder) holder,position);
//        }
    }

    private void onBindEmptyViewHolder(EmptyViewHolder holder, int position) {
        holder.tv_empty.setOnClickListener(v -> {
            listener.refresh();
        });
    }


    public void onBindSelectClassViewHolder(@NonNull SelectClassViewHolder holder, int position) {
        GradeBean gradeBean = list.get(position);
        holder.tv_class.setText(gradeBean.getGradeName());

        if (selectPostion==position){
            holder.tv_class.setSelected(true);
//            holder.tv_class.setTextColor(ContextCompat.getColor(context,R.color.white));
        }else {
//            holder.tv_class.setTextColor(ContextCompat.getColor(context,R.color.color_666666));
            holder.tv_class.setSelected(false);

        }
        LinearLayout.LayoutParams params = (LinearLayout.LayoutParams) holder.tv_class.getLayoutParams();
        if (position%3==0){
            params.gravity= Gravity.LEFT;
        }else if (position%3==1){
            params.gravity= Gravity.CENTER_HORIZONTAL;
        }else {
            params.gravity= Gravity.RIGHT;
        }

        holder.tv_class.setOnClickListener(view -> {
            listener.selected(position,list);
        });
    }

    @Override
    public int getItemViewType(int position) {
        if (list==null || list.size()==0){
            return TYPE_EMPTY;
        }else {

            return TYPE_DATA;
        }
    }

    @Override
    public int getItemCount() {
        return list==null || list.size()==0 ?1:list.size();
    }

    private int selectPostion=-1;
    public void update(int postion){
        selectPostion=postion;
        notifyDataSetChanged();
    }

    public void setNewData(List gradeBeans) {
        if (gradeBeans==null){
            return;
        }
        list.clear();
        list.addAll(gradeBeans);
        notifyDataSetChanged();
    }

    public interface onClickListener{
        void selected(int position, List list);

        void refresh();

    }



    class SelectClassViewHolder extends RecyclerView.ViewHolder{

        TextView tv_class;
        public SelectClassViewHolder(@NonNull View itemView) {
            super(itemView);
            tv_class=itemView.findViewById(R.id.tv_class);
        }
    }

    class EmptyViewHolder extends RecyclerView.ViewHolder{

        TextView tv_empty;
        public EmptyViewHolder(@NonNull View itemView) {
            super(itemView);
            tv_empty=itemView.findViewById(R.id.tv_empty);
        }
    }

}

rlv_user_msg_select_class_item:

rlv_select_class_empty_item:

注意事项：
1.不能自定义的网格分割线binding.rlvGrade.addItemDecoration(gridSpacingItemDecoration);
原因： setSpanSizeLookup中getSpanSize返回3时还在计算间隔距离，可以再自定义的分割线GridDividerItemDecoration中getItemOffsets的方法中添加判断传入的viewType不去计算距离（个人观点）

解决方法：不使用自定义的分割线，使用代码控制距离

    LinearLayout.LayoutParams params = (LinearLayout.LayoutParams) holder.tv_class.getLayoutParams();
        if (position%3==0){
            params.gravity= Gravity.LEFT;
        }else if (position%3==1){
            params.gravity= Gravity.CENTER_HORIZONTAL;
        }else {
            params.gravity= Gravity.RIGHT;
        }

注意：当作为父layout的LinearLayout的属性为android:orientation="vertical" 的时候，android:layout_gravity="？"这里设为横向的时候才能生效。比如：left，right，center_horizontal等

当作为父layout的LinearLayout的属性为android:orientation="horizental" 的时候，android:layout_gravity="？"这里设为纵向的时候才能生效。比如：top，bottom，center_vertical等；