Android RecyclerView更新子项目notifyItemChanged

在过去Android的ListView中，如果ListView中某一个或者一批项目发生变化，需要通过adapter的notifyDataSetChanged更新数据到最新，但是从ListView演进到现在的RecyclerView，数据的更新不需要像ListView那样notifyDataSetChanged，而是要采用RecyclerView的notifyItemChanged，传入一个pos位置，通知RecyclerView该pos位置已经失效，需要重新绘制和UI更新。现在给出一个例子，上面一个Button按钮，下面一个RecyclerView：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="随机更新" />

    <android.support.v7.widget.RecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</LinearLayout>

每次点击Button按钮，将随机更新某一个位置的时间到最新：

package zhangphil.demo;

import android.app.Activity;
import android.graphics.Color;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.LinearLayout;
import android.widget.TextView;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.Random;


public class MainActivity extends Activity {
    private ArrayList data = new ArrayList();

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

        for (int i = 0; i < 5; i++) {
            data.add(System.currentTimeMillis());
        }

        RecyclerView mRecyclerView = findViewById(R.id.recycler_view);

        LinearLayoutManager mLayoutManager = new LinearLayoutManager(this);
        mLayoutManager.setOrientation(LinearLayout.VERTICAL);
        mRecyclerView.setLayoutManager(mLayoutManager);

        final RecyclerView.Adapter mAdapter = new MyAdapter();
        mRecyclerView.setAdapter(mAdapter);

        final Random random = new Random();

        findViewById(R.id.button).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                int pos = random.nextInt(data.size());
                data.set(pos, System.currentTimeMillis());
                mAdapter.notifyItemChanged(pos);

                Toast.makeText(getApplicationContext(), "更新:" + pos + "," + data.get(pos), Toast.LENGTH_LONG).show();
            }
        });
    }


    private class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> {
        public MyAdapter() {
            super();
        }

        @Override
        public ViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
            View view = LayoutInflater.from(getApplicationContext()).inflate(android.R.layout.simple_list_item_2, null);
            ViewHolder holder = new ViewHolder(view);
            return holder;
        }

        @Override
        public void onBindViewHolder(ViewHolder viewHolder, int i) {
            viewHolder.text1.setText(i + "");
            viewHolder.text2.setText(data.get(i) + "");
        }

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

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

            public ViewHolder(View itemView) {
                super(itemView);
                text1 = itemView.findViewById(android.R.id.text1);
                text1.setTextColor(Color.RED);
                text2 = itemView.findViewById(android.R.id.text2);
                text2.setTextColor(Color.BLUE);
            }
        }
    }
}

事实上RecyclerView的notifyItemChanged的底层调用的是notifyItemRangeChanged：

 /**
         * Notify any registered observers that the item at <code>position</code> has changed.
         * Equivalent to calling <code>notifyItemChanged(position, null);</code>.
         *
         * <p>This is an item change event, not a structural change event. It indicates that any
         * reflection of the data at <code>position</code> is out of date and should be updated.
         * The item at <code>position</code> retains the same identity.</p>
         *
         * @param position Position of the item that has changed
         *
         * @see #notifyItemRangeChanged(int, int)
         */
        public final void notifyItemChanged(int position) {
            mObservable.notifyItemRangeChanged(position, 1);
        }

该方法使得RecyclerView批量范围内（range）数据更新，notifyItemChanged巧妙的将第二个参数计数器设置为1得以实现。后续再介绍RecyclerView的notifyItemRangeChanged。