我试图弄清楚更新RecyclerView的适配器有什么问题。
在我得到一个新的产品清单后，我试着:
Update the ArrayList from the fragment where recyclerView is created, set new data to adapter, and then call adapter.notifyDataSetChanged(); it did not work.
Create a new adapter, as others did, and it worked for them, but there wasn't any change for me: recyclerView.setAdapter(new RecyclerViewAdapter(newArrayList))
Create a method in Adapter which updates the data as follows:
public void updateData(ArrayList<ViewModel> viewModels) {
items.clear();
items.addAll(viewModels);
notifyDataSetChanged();
}
Then I call this method whenever I want to update the data list; it did not work.
To check if I can modify the recyclerView in any way, and I tried to remove at least an item:
public void removeItem(int position) {
items.remove(position);
notifyItemRemoved(position);
}
一切都保持原样。
这是我的适配器:
public class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerViewAdapter.ViewHolder> implements View.OnClickListener {
private ArrayList<ViewModel> items;
private OnItemClickListener onItemClickListener;
public RecyclerViewAdapter(ArrayList<ViewModel> items) {
this.items = items;
}
public void setOnItemClickListener(OnItemClickListener onItemClickListener) {
this.onItemClickListener = onItemClickListener;
}
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_recycler, parent, false);
v.setOnClickListener(this);
return new ViewHolder(v);
}
public void updateData(ArrayList<ViewModel> viewModels) {
items.clear();
items.addAll(viewModels);
notifyDataSetChanged();
}
public void addItem(int position, ViewModel viewModel) {
items.add(position, viewModel);
notifyItemInserted(position);
}
public void removeItem(int position) {
items.remove(position);
notifyItemRemoved(position);
}
@Override
public void onBindViewHolder(ViewHolder holder, int position) {
ViewModel item = items.get(position);
holder.title.setText(item.getTitle());
Picasso.with(holder.image.getContext()).load(item.getImage()).into(holder.image);
holder.price.setText(item.getPrice());
holder.credit.setText(item.getCredit());
holder.description.setText(item.getDescription());
holder.itemView.setTag(item);
}
@Override
public int getItemCount() {
return items.size();
}
@Override
public void onClick(final View v) {
// Give some time to the ripple to finish the effect
if (onItemClickListener != null) {
new Handler().postDelayed(new Runnable() {
@Override
public void run() {
onItemClickListener.onItemClick(v, (ViewModel) v.getTag());
}
}, 0);
}
}
protected static class ViewHolder extends RecyclerView.ViewHolder {
public ImageView image;
public TextView price, credit, title, description;
public ViewHolder(View itemView) {
super(itemView);
image = (ImageView) itemView.findViewById(R.id.image);
price = (TextView) itemView.findViewById(R.id.price);
credit = (TextView) itemView.findViewById(R.id.credit);
title = (TextView) itemView.findViewById(R.id.title);
description = (TextView) itemView.findViewById(R.id.description);
}
}
public interface OnItemClickListener {
void onItemClick(View view, ViewModel viewModel);
}
}
我启动RecyclerView，如下所示:
recyclerView = (RecyclerView) view.findViewById(R.id.recycler);
recyclerView.setLayoutManager(new GridLayoutManager(getActivity(), 5));
adapter = new RecyclerViewAdapter(items);
adapter.setOnItemClickListener(this);
recyclerView.setAdapter(adapter);
那么，如何实际更新适配器数据以显示新接收到的项呢?
问题是gridView的布局是这样的:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:tag="catalog_fragment"
android:layout_height="match_parent">
<FrameLayout
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
<android.support.v7.widget.RecyclerView
android:id="@+id/recycler"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:clipToPadding="false"/>
<ImageButton
android:id="@+id/fab"
android:layout_gravity="top|end"
style="@style/FabStyle"/>
</FrameLayout>
</LinearLayout>
然后我只是删除线性布局，并使FrameLayout作为父布局。
这是一个普遍的答案。本文解释了更新适配器数据的各种方法。该过程每次包括两个主要步骤:
更新数据集
将更改通知适配器
插入单个项目
在索引2中添加“Pig”。
String item = "Pig";
int insertIndex = 2;
data.add(insertIndex, item);
adapter.notifyItemInserted(insertIndex);
插入多个项目
在索引2处再插入三只动物。
ArrayList<String> items = new ArrayList<>();
items.add("Pig");
items.add("Chicken");
items.add("Dog");
int insertIndex = 2;
data.addAll(insertIndex, items);
adapter.notifyItemRangeInserted(insertIndex, items.size());
删除一个项目
从列表中删除“猪”。
int removeIndex = 2;
data.remove(removeIndex);
adapter.notifyItemRemoved(removeIndex);
移除多个项目
从列表中删除“骆驼”和“绵羊”。
int startIndex = 2; // inclusive
int endIndex = 4; // exclusive
int count = endIndex - startIndex; // 2 items will be removed
data.subList(startIndex, endIndex).clear();
adapter.notifyItemRangeRemoved(startIndex, count);
移除所有物品
清除整个列表。
data.clear();
adapter.notifyDataSetChanged();
用新列表替换旧列表
清除旧列表，然后添加一个新列表。
// clear old list
data.clear();
// add new list
ArrayList<String> newList = new ArrayList<>();
newList.add("Lion");
newList.add("Wolf");
newList.add("Bear");
data.addAll(newList);
// notify adapter
adapter.notifyDataSetChanged();
适配器有一个对数据的引用，所以我没有将数据设置为一个新对象是很重要的。相反，我从数据中清除了旧项，然后添加了新的项。
更新单项
将“Sheep”项更改为“I like Sheep”。
String newValue = "I like sheep.";
int updateIndex = 3;
data.set(updateIndex, newValue);
adapter.notifyItemChanged(updateIndex);
移动单个物品
将“羊”从位置3移动到位置1。
int fromPosition = 3;
int toPosition = 1;
// update data array
String item = data.get(fromPosition);
data.remove(fromPosition);
data.add(toPosition, item);
// notify adapter
adapter.notifyItemMoved(fromPosition, toPosition);
Code
这里是项目代码供您参考。RecyclerView适配器代码可以在这个答案中找到。
MainActivity.java
public class MainActivity extends AppCompatActivity implements MyRecyclerViewAdapter.ItemClickListener {
List<String> data;
MyRecyclerViewAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// data to populate the RecyclerView with
data = new ArrayList<>();
data.add("Horse");
data.add("Cow");
data.add("Camel");
data.add("Sheep");
data.add("Goat");
// set up the RecyclerView
RecyclerView recyclerView = findViewById(R.id.rvAnimals);
LinearLayoutManager layoutManager = new LinearLayoutManager(this);
recyclerView.setLayoutManager(layoutManager);
DividerItemDecoration dividerItemDecoration = new DividerItemDecoration(recyclerView.getContext(),
layoutManager.getOrientation());
recyclerView.addItemDecoration(dividerItemDecoration);
adapter = new MyRecyclerViewAdapter(this, data);
adapter.setClickListener(this);
recyclerView.setAdapter(adapter);
}
@Override
public void onItemClick(View view, int position) {
Toast.makeText(this, "You clicked " + adapter.getItem(position) + " on row number " + position, Toast.LENGTH_SHORT).show();
}
public void onButtonClick(View view) {
insertSingleItem();
}
private void insertSingleItem() {
String item = "Pig";
int insertIndex = 2;
data.add(insertIndex, item);
adapter.notifyItemInserted(insertIndex);
}
private void insertMultipleItems() {
ArrayList<String> items = new ArrayList<>();
items.add("Pig");
items.add("Chicken");
items.add("Dog");
int insertIndex = 2;
data.addAll(insertIndex, items);
adapter.notifyItemRangeInserted(insertIndex, items.size());
}
private void removeSingleItem() {
int removeIndex = 2;
data.remove(removeIndex);
adapter.notifyItemRemoved(removeIndex);
}
private void removeMultipleItems() {
int startIndex = 2; // inclusive
int endIndex = 4; // exclusive
int count = endIndex - startIndex; // 2 items will be removed
data.subList(startIndex, endIndex).clear();
adapter.notifyItemRangeRemoved(startIndex, count);
}
private void removeAllItems() {
data.clear();
adapter.notifyDataSetChanged();
}
private void replaceOldListWithNewList() {
// clear old list
data.clear();
// add new list
ArrayList<String> newList = new ArrayList<>();
newList.add("Lion");
newList.add("Wolf");
newList.add("Bear");
data.addAll(newList);
// notify adapter
adapter.notifyDataSetChanged();
}
private void updateSingleItem() {
String newValue = "I like sheep.";
int updateIndex = 3;
data.set(updateIndex, newValue);
adapter.notifyItemChanged(updateIndex);
}
private void moveSingleItem() {
int fromPosition = 3;
int toPosition = 1;
// update data array
String item = data.get(fromPosition);
data.remove(fromPosition);
data.add(toPosition, item);
// notify adapter
adapter.notifyItemMoved(fromPosition, toPosition);
}
}
笔记
如果使用notifyDataSetChanged()，则不会执行动画。这也可能是一个代价高昂的操作，因此如果您只更新单个项或一组项，则不建议使用notifyDataSetChanged()。
如果您正在对列表进行较大或复杂的更改，请检查DiffUtil。
进一步的研究
CodePath:使用RecyclerView
使用DiffUtil更新RecyclerView的聪明方法
我强烈推荐您使用[DiffUtil。ItemCallback][1]来处理RecyclerView中的变化。适配器:
fun setData(data: List<T>) {
val calculateDiff = DiffUtil.calculateDiff(DiffUtilCallback(items, data))
items.clear()
items += data
calculateDiff.dispatchUpdatesTo(this)
}
在底层，它用AdapterListUpdateCallback处理大部分事情:
/**
* ListUpdateCallback that dispatches update events to the given adapter.
*
* @see DiffUtil.DiffResult#dispatchUpdatesTo(RecyclerView.Adapter)
*/
public final class AdapterListUpdateCallback implements ListUpdateCallback {
@NonNull
private final RecyclerView.Adapter mAdapter;
/**
* Creates an AdapterListUpdateCallback that will dispatch update events to the given adapter.
*
* @param adapter The Adapter to send updates to.
*/
public AdapterListUpdateCallback(@NonNull RecyclerView.Adapter adapter) {
mAdapter = adapter;
}
/** {@inheritDoc} */
@Override
public void onInserted(int position, int count) {
mAdapter.notifyItemRangeInserted(position, count);
}
/** {@inheritDoc} */
@Override
public void onRemoved(int position, int count) {
mAdapter.notifyItemRangeRemoved(position, count);
}
/** {@inheritDoc} */
@Override
public void onMoved(int fromPosition, int toPosition) {
mAdapter.notifyItemMoved(fromPosition, toPosition);
}
/** {@inheritDoc} */
@Override
public void onChanged(int position, int count, Object payload) {
mAdapter.notifyItemRangeChanged(position, count, payload);
}
}
