Android RecyclerView更新子项目notifyItemChanged

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。