Android StaggeredGridLayoutManager布局RecyclerView在滚动状态可见范围刷新数据

之所以把StaggeredGridLayoutManager布局的RecyclerView单列出来处理滚动状态下可见（可视）范围内的数据更新问题，是因为在StaggeredGridLayoutManager布局下的RecyclerView，对于第一个可视item和最后一个可视item，即第一个可视item位置和最后一个可视item位置，不像在LinearLayoutManager布局下直接获取，需要进行一个简单计算。关键的计算过程我写在了getOutRange()方法内。

package zhangphil.recyclerview;

import android.graphics.Color;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.StaggeredGridLayoutManager;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.Arrays;

public class RecyclerViewActivity extends AppCompatActivity {
    private RecyclerView mRecyclerView;
    private RecyclerViewAdapter mAdapter;
    private StaggeredGridLayoutManager layoutManager;
    private ArrayList<String> mItems;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.recycler_view_activity);

        mItems = new ArrayList<>();
        for (int i = 0; i < 110; i++) {
            mItems.add(i + "");
        }

        initRecyclerView();

        mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                super.onScrollStateChanged(recyclerView, newState);

                if (recyclerView.getScrollState() == RecyclerView.SCROLL_STATE_IDLE) {
                    int[] outRange = getOutRange();
                    int len = outRange[1] - outRange[0] + 1;

                    int num = (int) (Math.random() * 10);
                    for (int i = 0; i < len; i++) {
                        mItems.set(outRange[0] + i, num + "");
                    }

                    mAdapter.notifyDataSetChanged();
                }
            }
        });
    }

    private int[] getOutRange() {
        int[] range = new int[2];

        int[] first = new int[layoutManager.getSpanCount()];
        layoutManager.findFirstVisibleItemPositions(first);

        int[] last = new int[layoutManager.getSpanCount()];
        layoutManager.findLastVisibleItemPositions(last);

        range[0] = first[0];

        Arrays.sort(last);
        range[1] = last[last.length - 1];

        return range;
    }

    private void initRecyclerView() {
        mRecyclerView = findViewById(R.id.recycler_view);
        layoutManager = new StaggeredGridLayoutManager(3, StaggeredGridLayoutManager.VERTICAL);
        mRecyclerView.setLayoutManager(layoutManager);

        mAdapter = new RecyclerViewAdapter();
        mRecyclerView.setAdapter(mAdapter);
    }

    private class RecyclerViewAdapter extends RecyclerView.Adapter<MyVH> {

        @NonNull
        @Override
        public MyVH onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
            View view = LayoutInflater.from(getApplicationContext()).inflate(android.R.layout.simple_list_item_2, parent, false);
            return new MyVH(view);
        }

        @Override
        public void onBindViewHolder(@NonNull MyVH holder, int position) {
            holder.text1.setText("" + position);
            holder.text2.setText(mItems.get(position));
        }

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

    private class MyVH extends RecyclerView.ViewHolder {
        public TextView text1;
        public TextView text2;

        public MyVH(View itemView) {
            super(itemView);
            text1 = itemView.findViewById(android.R.id.text1);
            text1.setTextColor(Color.WHITE);
            text1.setBackgroundColor(Color.RED);
            text2 = itemView.findViewById(android.R.id.text2);
            text2.setTextColor(Color.DKGRAY);
        }
    }
}

代码实现一个简单意图，用StaggeredGridLayoutManager控制RecyclerView，当RecyclerView滚动停止后，更新可可范围内的数据到最新。

如图：