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/*
* Copyright (C) 2017 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package android.support.v7.recyclerview.extensions;
import android.support.annotation.NonNull;
import android.support.v7.widget.RecyclerView;
import java.util.List;
/**
* {@link RecyclerView.Adapter RecyclerView.Adapter} base class for presenting List data in a
* {@link RecyclerView}, including computing diffs between Lists on a background thread.
* <p>
* This class is a convenience wrapper around ListAdapterHelper that implements common default
* behavior for item access and counting.
* <p>
* While using a LiveData<List> is an easy way to provide data to the adapter, it isn't required
* - you can use {@link #setList(List)} when new lists are available.
* <p>
* A complete usage pattern with Room would look like this:
* <pre>
* {@literal @}Dao
* interface UserDao {
* {@literal @}Query("SELECT * FROM user ORDER BY lastName ASC")
* public abstract LiveData<List<User>> usersByLastName();
* }
*
* class MyViewModel extends ViewModel {
* public final LiveData<List<User>> usersList;
* public MyViewModel(UserDao userDao) {
* usersList = userDao.usersByLastName();
* }
* }
*
* class MyActivity extends AppCompatActivity {
* {@literal @}Override
* public void onCreate(Bundle savedState) {
* super.onCreate(savedState);
* MyViewModel viewModel = ViewModelProviders.of(this).get(MyViewModel.class);
* RecyclerView recyclerView = findViewById(R.id.user_list);
* UserAdapter<User> adapter = new UserAdapter();
* viewModel.usersList.observe(this, list -> adapter.setList(list));
* recyclerView.setAdapter(adapter);
* }
* }
*
* class UserAdapter extends ListAdapter<User, UserViewHolder> {
* public UserAdapter() {
* super(User.DIFF_CALLBACK);
* }
* {@literal @}Override
* public void onBindViewHolder(UserViewHolder holder, int position) {
* holder.bindTo(getItem(position));
* }
* }
*
* {@literal @}Entity
* class User {
* // ... simple POJO code omitted ...
*
* public static final DiffCallback<User> DIFF_CALLBACK = new DiffCallback<Customer>() {
* {@literal @}Override
* public boolean areItemsTheSame(
* {@literal @}NonNull User oldUser, {@literal @}NonNull User newUser) {
* // User properties may have changed if reloaded from the DB, but ID is fixed
* return oldUser.getId() == newUser.getId();
* }
* {@literal @}Override
* public boolean areContentsTheSame(
* {@literal @}NonNull User oldUser, {@literal @}NonNull User newUser) {
* // NOTE: if you use equals, your object must properly override Object#equals()
* // Incorrectly returning false here will result in too many animations.
* return oldUser.equals(newUser);
* }
* }
* }</pre>
*
* Advanced users that wish for more control over adapter behavior, or to provide a specific base
* class should refer to {@link ListAdapterHelper}, which provides custom mapping from diff events
* to adapter positions.
*
* @param <T> Type of the Lists this Adapter will receive.
* @param <VH> A class that extends ViewHolder that will be used by the adapter.
*/
public abstract class ListAdapter<T, VH extends RecyclerView.ViewHolder>
extends RecyclerView.Adapter<VH> {
private final ListAdapterHelper<T> mHelper;
@SuppressWarnings("unused")
protected ListAdapter(@NonNull DiffCallback<T> diffCallback) {
mHelper = new ListAdapterHelper<>(new ListAdapterHelper.AdapterCallback(this),
new ListAdapterConfig.Builder<T>().setDiffCallback(diffCallback).build());
}
@SuppressWarnings("unused")
protected ListAdapter(@NonNull ListAdapterConfig<T> config) {
mHelper = new ListAdapterHelper<>(new ListAdapterHelper.AdapterCallback(this), config);
}
/**
* Set the new list to be displayed.
* <p>
* If a list is already being displayed, a diff will be computed on a background thread, which
* will dispatch Adapter.notifyItem events on the main thread.
*
* @param list The new list to be displayed.
*/
public void setList(List<T> list) {
mHelper.setList(list);
}
@SuppressWarnings("unused")
protected T getItem(int position) {
return mHelper.getItem(position);
}
@Override
public int getItemCount() {
return mHelper.getItemCount();
}
}
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