最近有接到分頁的需求, 想當然準備使用監聽onScroll然後分段加載, 看到谷歌爸爸出品了Jetpack系列文章有Paging Lib於是點開看了下, 介紹的太複雜了有木有!!! room什麼鬼, ViewModel云云
也許是因爲谷歌想推room, 但是隻想了解分頁的我完全看不下去了, 簡單Demo入門, 記錄如下
新建Activity, 我使用的Fragment+ViewModel的方式, 很方便
1.導入依賴
implementation 'android.arch.lifecycle:extensions:1.1.1'
implementation 'android.arch.paging:runtime:1.0.0'
implementation 'com.android.support:recyclerview-v7:27.0.2'
//可選, 我習慣使用約束佈局
implementation 'com.android.support.constraint:constraint-layout:1.1.3'
版本不同方法可能有差異, 建議初學使用我這的版本, 方便跟着後面走
首先照着後面的代碼複製一遍, 大概知道有哪些東西
2.新建實體類
class Concert {
public int id;
private String name;
public Concert(int id, String name) {
this.id = id;
this.name = name;
}
@Override
public String toString() {
return "Concert{" +
"id=" + id +
", name='" + name + '\'' +
'}';
}
@Override
public int hashCode() {
return id + name.hashCode();
}
@Override
public boolean equals( Object obj) {
if (obj instanceof Concert){
boolean b = ((Concert) obj).id == id && ((Concert) obj).name.equals(name);
return b;
}else {
return false;
}
}
}
//使用到的佈局R.layout.paged_list_fragment
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/pagedlist"
android:layout_width="match_parent"
android:layout_height="match_parent"
>
<android.support.v7.widget.RecyclerView
android:id="@+id/recyclerView"
android:layout_width="0dp"
android:layout_height="256dp"
android:layout_marginStart="8dp"
android:layout_marginTop="8dp"
android:layout_marginEnd="8dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>
//R.layout.item_concert_list
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/name"
android:layout_width="match_parent"
android:layout_height="match_parent">
<TextView
android:id="@+id/textView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="8dp"
android:layout_marginBottom="8dp"
android:text="TextView"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>
3.新建DataSource實現類
import android.arch.paging.PositionalDataSource;
import android.support.annotation.NonNull;
import android.util.Log;
import java.util.ArrayList;
import java.util.List;
public class PositionPageDataSource extends PositionalDataSource<Concert> {
@Override
public void loadInitial(@NonNull LoadInitialParams params, @NonNull LoadInitialCallback<Concert> callback) {
int requestedLoadSize = params.requestedLoadSize;
Log.d("ldo","PositionPageDataSource loadInitial "+requestedLoadSize);
List<Concert> subList = getSubList(0, requestedLoadSize);
callback.onResult(subList,0,40);
}
@Override
public void loadRange(@NonNull LoadRangeParams params, @NonNull LoadRangeCallback<Concert> callback) {
Log.d("ldo","PositionPageDataSource loadRange");
callback.onResult(getSubList(params.startPosition,20));
}
public List<Concert> getSubList(int start, int end) {
Log.d("ldo", "getSubList");
ArrayList<Concert> strings = new ArrayList<>();
for (int i = 0; i < end; i++) {
strings.add(new Concert(start, "" + i));
}
return strings;
}
}
//Factory
import android.arch.paging.DataSource;
public class DataSourceFactorty extends DataSource.Factory<Integer,Concert> {
@Override
public DataSource<Integer,Concert> create() {
return new PositionPageDataSource();
}
}
4.新建Adapter
import android.arch.paging.PagedListAdapter;
import android.support.annotation.NonNull;
import android.support.v7.util.DiffUtil;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
public class ConcertAdapter extends PagedListAdapter<Concert, ConcertAdapter.ViewHolder> {
ConcertAdapter() {
super(showDiffCallBack);
}
static DiffUtil.ItemCallback<Concert> showDiffCallBack = new DiffUtil.ItemCallback<Concert>() {
@Override
public boolean areItemsTheSame(@NonNull Concert oldItem, @NonNull Concert newItem) {
return (oldItem).id == (newItem).id;
}
@Override
public boolean areContentsTheSame(@NonNull Concert oldItem, @NonNull Concert newItem) {
return oldItem.equals(newItem);
}
};
@NonNull
@Override
public ConcertAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
return new ViewHolder(LayoutInflater.from(parent.getContext()).inflate(R.layout.item_concert_list, null));
}
@Override
public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
Concert concert = getItem(position);
holder.v.setText(concert.getId()+"");
}
public class ViewHolder extends RecyclerView.ViewHolder {
TextView v;
public ViewHolder(@NonNull View itemView) {
super(itemView);
this.v = itemView.findViewById(R.id.textView);
}
}
}
5.新建Fragment
import android.arch.lifecycle.LiveData;
import android.arch.lifecycle.Observer;
import android.arch.paging.LivePagedListBuilder;
import android.arch.paging.PagedList;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import com.example.android.displayingbitmaps.R;
public class PagedListFragment extends Fragment {
private RecyclerView recyclerView;
public static final int INITIALLOADSIZE = 40;//初始加載數量
public static final int RELOADSIZE = 20;//往下滑動加載數量
private LiveData<PagedList<Concert>> data;
private ConcertAdapter adapter;
public static PagedListFragment newInstance() {
return new PagedListFragment();
}
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,
@Nullable Bundle savedInstanceState) {
View inflate = inflater.inflate(R.layout.paged_list_fragment, container, false);
recyclerView = inflate.findViewById(R.id.recyclerView);
return inflate;
}
@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
PagedList.Config config = new PagedList.Config.Builder()
.setPageSize(INITIALLOADSIZE) // 分頁加載的數量
.setEnablePlaceholders(false) // 當item爲null是否使用PlaceHolder展示
.setInitialLoadSizeHint(RELOADSIZE) // 預加載的數量
// .setPrefetchDistance(5)
.build();
data = new LivePagedListBuilder(new DataSourceFactorty(), config).build();//可以放在ViewModel層處理
data.observe(this, new Observer<PagedList<Concert>>() {
@Override
public void onChanged(@Nullable PagedList<Concert> concerts) {
Log.d("ldo","onChanged "+concerts.size());
adapter.submitList(concerts);//調用PagedListAdapter中的方法綁定
}
});
adapter = new ConcertAdapter();
recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
recyclerView.setAdapter(adapter);
}
}
有一個大概認知之後簡單介紹一下各個部分
- DataSource
數據處理核心, 最終回調到PagedList - LivePagedListBuilder
關聯DataSource和觀察數據 - PagedList
可以理解爲存儲數據的集合容器, 不需要我們過多關注 - PagedListAdapter
配合recycleview使用
需要注意的是adapter.submitList(concerts)使用父類的方法設置集合, 採取自己設置list然後notifyDataChaged的方式, PositionPageDataSource裏面的方法不會回調
不同DataSource實現類的區別
目前有三種DataSource實現方式, 上面使用的是PositionalDataSource, 想必你已經看到效果了
- PositionalDataSource
適用於上拉加載更多的場景, 如京東商城列表瀏覽, 知乎等 - ItemKeyedDataSource
適用於下一part內容依賴當前某個key來獲取, 如獲得下一part的專輯列表, 需要傳入當前歌手來獲取 - PageKeyedDataSource
適用於有明顯上下頁的場景, 如支持上一章,下一章跳轉可以使用此種方式