Question

最近我使用RecyclerView并添加自定义标题视图（另一种类型的项目视图）并尝试在数据更改时更新它。奇怪的事发生了。适配器创建一个新的HeaderViewHolder，并使用新的HeaderViewHolder和旧的HeaderViewHolder。

这是样本。

MainActivity.java

public class MainActivity extends ActionBarActivity {

  private RecyclerView mRecyclerView;

  private MyAdapter mAdapter;

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

    mRecyclerView = (RecyclerView) findViewById(R.id.list);
    LinearLayoutManager llm = new LinearLayoutManager(this);
    llm.setSmoothScrollbarEnabled(true);
    mRecyclerView.setLayoutManager(llm);
    mRecyclerView.setAdapter(mAdapter = new MyAdapter(this, genItemList()));
  }

  @Override public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
  }

  @Override public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings) {
      return true;
    }

    return super.onOptionsItemSelected(item);
  }

  public void addItems(View view) {
    mAdapter.addItemList(genItemList());
  }

  private List<Item> genItemList() {
    List<Item> list = new ArrayList<>(50);
    for (int i = 0; i < 50; i++) {
      Item item = new Item();
      item.text1 = "AAAAAAAAAAAAAAAAAAAAAAAA";
      item.text2 = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";
      list.add(item);
    }
    return list;
  }

  public void updateHeader(View view) {
    mAdapter.updateHeader("Updated header");
  }
}

MyAdapter.java

public class MyAdapter extends RecyclerView.Adapter {

  private static final String TAG = "MyAdapter";

  private static final int TYPE_HEADER = 0;
  private static final int TYPE_ITEM   = 1;

  private LayoutInflater mInflater;

  private List<Item> mItemList;

  private Header mHeader;

  public MyAdapter(Context context, List<Item> items) {
    mInflater = LayoutInflater.from(context);
    mItemList = items != null ? items : new ArrayList<Item>();
    mHeader = new Header();
    mHeader.text = "header";
  }

  @Override public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup viewGroup, int type) {
    switch (type) {
    case TYPE_HEADER:
      Log.d(TAG, "create header view holder");
      View headerView = mInflater.inflate(android.R.layout.simple_list_item_1, viewGroup, false);
      return new HeaderViewHolder(headerView);
    case TYPE_ITEM:
      View itemView = mInflater.inflate(R.layout.layout_item, viewGroup, false);
      return new MyViewHolder(itemView);
    }
    return null;
  }

  @Override public void onBindViewHolder(RecyclerView.ViewHolder viewHolder, int position) {
    if (viewHolder instanceof HeaderViewHolder) {
      Log.d(TAG, "bind header view holder");
      TextView textView = (TextView) viewHolder.itemView.findViewById(android.R.id.text1);
      textView.setText(mHeader.text);
      Log.d(TAG, "position: " + position + " holder: " + viewHolder + " text: " + mHeader.text);
    } else if (viewHolder instanceof MyViewHolder) {
      Item item = mItemList.get(position - 1)
      ((MyViewHolder) viewHolder).setText1(item.text1);
      ((MyViewHolder) viewHolder).setText2(item.text2);
    }
  }

  @Override public int getItemCount() {
    return mItemList == null ? 0 : mItemList.size() + 1; // plus header
  }

  @Override public int getItemViewType(int position) {
    return position == 0 ? TYPE_HEADER : TYPE_ITEM;
  }

  public void addItemList(List<Item> list) {
    if (list != null) {
      mItemList.addAll(list);
      notifyDataSetChanged();
    }
  }

  public void updateHeader(String text) {
    mHeader.text = text;
    notifyItemChanged(0);
    // notifyDataSetChanged();
  }

  static class HeaderViewHolder extends RecyclerView.ViewHolder {

    public HeaderViewHolder(View itemView) {
      super(itemView);
    }
  }

  static class MyViewHolder extends RecyclerView.ViewHolder {

    TextView mTextView1;
    TextView mTextView2;

    public MyViewHolder(View itemView) {
      super(itemView);

      mTextView1 = (TextView) itemView.findViewById(R.id.text1);
      mTextView2 = (TextView) itemView.findViewById(R.id.text2);
    }

    public void setText1(String text) {
      mTextView1.setText(text);
    }

    public void setText2(String text) {
      mTextView2.setText(text);
    }
  }
}

Header.java

public class Header {

  public String text;
}

Item.java

public class Item {

  public String text1;
  public String text2;
}

activity_main.xml中

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

  <android.support.v7.widget.RecyclerView
      android:id="@+id/list"
      android:layout_width="match_parent"
      android:layout_height="0dp"
      android:layout_weight="1" />

  <LinearLayout
      style="?android:buttonBarStyle"
      android:layout_width="match_parent"
      android:layout_height="56dp"
      android:orientation="horizontal">

    <Button
        android:id="@+id/add"
        style="?android:buttonBarButtonStyle"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:onClick="addItems"
        android:text="Add items" />

    <Button
        android:id="@+id/update"
        style="?android:buttonBarButtonStyle"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="1"
        android:onClick="updateHeader"
        android:text="update header" />
  </LinearLayout>

</LinearLayout>

layout_item.xml

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

  <TextView
      android:id="@+id/text1"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:ellipsize="marquee"
      android:maxLines="1"
      android:textAppearance="?android:textAppearanceLarge"
      android:textColor="@android:color/black" />

  <TextView
      android:id="@+id/text2"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:ellipsize="marquee"
      android:maxLines="1"
      android:textAppearance="?android:textAppearanceSmall"
      android:textColor="@android:color/black" />

</LinearLayout>

然后，当我点击3次＆＃34;更新标题＆＃34;时，这里是logcat输出：

06-05 19:57:50.368  20400-20400/com.imaygou.recyclerupdateitemdemo D/MyAdapter﹕ create header view holder
06-05 19:57:50.369  20400-20400/com.imaygou.recyclerupdateitemdemo D/MyAdapter﹕ bind header view holder
06-05 19:57:50.370  20400-20400/com.imaygou.recyclerupdateitemdemo D/MyAdapter﹕ position: 0 holder: ViewHolder{3f742717 position=0 id=-1, oldPos=-1, pLpos:-1 no parent} text: header
06-05 19:57:54.030  20400-20400/com.imaygou.recyclerupdateitemdemo D/MyAdapter﹕ create header view holder
06-05 19:57:54.031  20400-20400/com.imaygou.recyclerupdateitemdemo D/MyAdapter﹕ bind header view holder
06-05 19:57:54.031  20400-20400/com.imaygou.recyclerupdateitemdemo D/MyAdapter﹕ position: 0 holder: ViewHolder{3ac01621 position=0 id=-1, oldPos=-1, pLpos:-1 no parent} text: Updated header
06-05 19:57:56.938  20400-20400/com.imaygou.recyclerupdateitemdemo D/MyAdapter﹕ bind header view holder
06-05 19:57:56.938  20400-20400/com.imaygou.recyclerupdateitemdemo D/MyAdapter﹕ position: 0 holder: ViewHolder{3f742717 position=0 id=-1, oldPos=-1, pLpos:-1 no parent} text: Updated header
06-05 19:57:59.613  20400-20400/com.imaygou.recyclerupdateitemdemo D/MyAdapter﹕ bind header view holder
06-05 19:57:59.613  20400-20400/com.imaygou.recyclerupdateitemdemo D/MyAdapter﹕ position: 0 holder: ViewHolder{3ac01621 position=0 id=-1, oldPos=-1, pLpos:-1 no parent} text: Updated header

如果我使用notifyDataSetChanged()代替notifyItemChanged(0)，一切正常。没人多ViewHolder。但为什么？

为什么它会创建一个新的ViewHolder并同时使用它们？

使用notifyItemChanged(int)的最佳做法是什么？

Answer 1

RecyclerView使用ViewHolder同时实现从旧状态到新状态的平滑动画。这是RecyclerView.ItemAnimator的默认行为。

您可以通过将空项目动画传递给RecyclerView来禁用动画：

listView.setItemAnimator(null);

Answer 2

((SimpleItemAnimator) myRecyclerView.getItemAnimator()).setSupportsChangeAnimations(false);

Answer 3

在调用recyclerView.notifyItemChanged（）之后，为避免ViewHolder重新创建并且不禁用平滑动画，您可以设置DefaultItemAnimator并覆盖canReuseUpdatedViewHolder()方法。

科特琳：

val itemAnimator: DefaultItemAnimator = object : DefaultItemAnimator() {
      override fun canReuseUpdatedViewHolder(viewHolder: RecyclerView.ViewHolder): Boolean {
            return true
      }
}
recyclerView.itemAnimator = itemAnimator

Answer 4

以下是您实施的一些问题：

getItemCount需要包含标题的Recyclerview中所有项目的计数，因此您应该返回mItemList.size() + 1
onBindViewHolder（）中的position字段指的是整个recyclerview中元素的位置，包括标题。所以要绑定一个非标题项，你会做类似item = mItemList.get(position - 1)的事情 - 这不会失败因为getItemViewType为TYPE_ITEMs返回一个大于0的数字

通过这样做，notifyItemChanged应该按预期行事

Answer 5

您还可以将notifyItemChanged与有效载荷一起使用：https://developer.android.com/reference/android/support/v7/widget/RecyclerView.Adapter.html#notifyitemchanged。它将重用相同的ViewHolder实例：“如果该项目已经由ViewHolder表示，它将被反弹到相同的ViewHolder”

Answer 6

更清晰的解决方案（不是动画制作中的错误，但这是布局管理器的一项功能）：

mRecyclerView.setLayoutManager(new GridLayoutManager(this, 5, LinearLayoutManager.VERTICAL, false){
        @Override
        public boolean supportsPredictiveItemAnimations() {
            return false;//super.supportsPredictiveItemAnimations();
        }
    });

为什么RecyclerView.notifyItemChanged（）将创建一个新的ViewHolder并使用旧的ViewHolder和新的ViewHolder？

6 个答案: