Android RecyclerView更新子项目notifyItemChanged

比眉伴天荒 2024-02-18 16:31 30阅读 0赞

**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：

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。