Android RecyclerView更新子項目notifyItemChanged

Android RecyclerView更新子項目notifyItemChanged

在過去Android的ListView中，如果ListView中某一個或者一批項目發生變化，需要通過adapter的notifyDataSetChanged更新數據到最新，但是從ListView演進到現在的RecyclerView，數據的更新不需要像ListView那樣notifyDataSetChanged，而是要采用RecyclerView的notifyItemChanged，傳入一個pos位置，通知RecyclerView該pos位置已經失效，需要重新繪制和UI更新。現在給出一個例子，上面一個Button按鈕，下面一個RecyclerView：

每次點擊Button按鈕，將隨機更新某一個位置的時間到最新：

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 {
        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);
            }
        }
    }
}

事實上RecyclerView的notifyItemChanged的底層調用的是notifyItemRangeChanged：

 /**
         * Notify any registered observers that the item at position has changed.
         * Equivalent to calling notifyItemChanged(position, null);.
         *
         * 

This is an item change event, not a structural change event. It indicates that any * reflection of the data at position is out of date and should be updated. * The item at position retains the same identity.

* * @param position Position of the item that has changed * * @see #notifyItemRangeChanged(int, int) */ public final void notifyItemChanged(int position) { mObservable.notifyItemRangeChanged(position, 1); }

該方法使得RecyclerView批量范圍內（range）數據更新，notifyItemChanged巧妙的將第二個參數計數器設置為1得以實現。後續再介紹RecyclerView的notifyItemRangeChanged。