使用Paging的好处是什么
- 好处一:分页库可以更轻松地在应用程序中的RecyclerView逐步和优雅地加载数据;
- 好处二:数据请求消耗的网络带宽更少,系统资源更少;
- 好处三:即使在数据更新和刷新期间,应用程序仍会继续快速响应用户输入;
- 好处四:不过多浪费,显示多少就用多少;
Paging的使用
- 角色一:DataSource(是数据源,包含了多种形式,例如:Room来源,PositionalDataSource来源,PageKeyedDataSource来源,ItemKeyedDataSource来源)
- 角色二:PagedList(是UIModel数据层,通过Factory的方式拿到数据源)
- 角色三:PagedAdapter(注意,不再是之前使用RecycleView的那种适配器了,而是和Paging配套的PagedListAdapter)
- 角色四:RecycleView(是之前学的RecycleView,只不过setAdapter的时候,绑定的适配器是 PagedAdapter)
public class Student {
private String id;
private String name;
private String sex;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
// 比较的函数
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Student student = (Student) o;
return id.equals(student.id) &&
name.equals(student.name) &&
sex.equals(student.sex);
}
// 比较的函数
@RequiresApi(api = Build.VERSION_CODES.KITKAT)
@Override
public int hashCode() {
return Objects.hash(id, name, sex);
}
}
角色1 数据源
数据源就是数据的来源,可以有多种来源渠道,例如:“网络数据”,“本地数据”,“数据库数据”
public class StudentDataSource extends PositionalDataSource<Student> {
/**
* 可以理解是加载第一页数据的时候,会执行此函数来完成
* 加载初始化数据,可以这么来理解,加载的是第一页的数据。
* 形象的说,当我们第一次打开页面,需要回调此方法来获取数据。
* @param params
* @param callback
*/
@Override
public void loadInitial(@NonNull LoadInitialParams params, @NonNull LoadInitialCallback<Student> callback) {
// @1 数据源 @2 位置 @3 总大小
callback.onResult(getStudents(0, Flag.SIZE), 0, 1000);
}
/**
* 当有了初始化数据之后,滑动的时候如果需要加载数据的话,会调用此方法。
* @param params
* @param callback
*/
@Override
public void loadRange(@NonNull LoadRangeParams params, @NonNull LoadRangeCallback<Student> callback) {
// @1 从哪里开始加载(位置 内部算的) @2 size(size 内部算的)
callback.onResult(getStudents(params.startPosition, params.loadSize));
}
/**
* 可以理解这里是数据源,数据的来源(数据库,文件,网络服务器响应 等等)
* @param startPosition
* @param pageSize
* @return
*/
private List<Student> getStudents(int startPosition, int pageSize) {
List<Student> list = new ArrayList<>();
for (int i = startPosition; i < startPosition + pageSize; i++) {
Student student = new Student();
student.setId("ID号是:" + i);
student.setName("我名称:" + i);
student.setSex("我性别:" + i);
list.add(student);
}
return list;
}
}
角色2 数据工厂
创建管理数据源的工厂,为什么有一个工厂,除了可以去创建数据源之外,为了后续的扩展
/**
* 数据的工厂
*/
public class StudentDataSourceFactory extends DataSource.Factory<Integer, Student> {
@NonNull
@Override
public DataSource<Integer, Student> create() {
StudentDataSource studentDataSource = new StudentDataSource();
return studentDataSource;
}
}
角色3 数据模型
数据模型其实就是 ViewModel,用来管理数据
PagedList: 数据源获取的数据最终靠PagedList来承载。对于PagedList,我们可以这样来理解,它就是一页数据的集合。 每请求一页,就是新的一个PagedList对象。
public class StudentViewModel extends ViewModel {
// 看源码:@1 listLiveData 数据怎么来的
private final LiveData<PagedList<Student>> listLiveData;
public StudentViewModel() {
StudentDataSourceFactory factory = new StudentDataSourceFactory();
// 初始化 ViewModel
this.listLiveData = new LivePagedListBuilder<Integer, Student>(factory, Flag.SIZE).build();
}
// TODO 暴露数据出去
public LiveData<PagedList<Student>> getListLiveData() {
return listLiveData;
}
}
角色4 适配器
这个Adapter就是一个RecyclerView的Adapter。不过我们在使用paging实现RecyclerView的分页加载效果,不能直接继承RecyclerView的Adapter,而是需要继承PagedListAdapter。
LiveData观察到的数据,把感应到的数据给适配器,适配器又绑定了 RecyclerView,那么RecyclerView的列表数据就改变了
public class RecyclerPagingAdapter extends PagedListAdapter<Student, RecyclerPagingAdapter.MyRecyclerViewHolder> {
// TODO 比较的行为
private static DiffUtil.ItemCallback<Student> DIFF_STUDNET = new
DiffUtil.ItemCallback<Student>() {
// 一般是比较 唯一性的内容, ID
@Override
public boolean areItemsTheSame(@NonNull Student oldItem, @NonNull Student newItem) {
return oldItem.getId().equals(newItem.getId());
}
// 对象本身的比较
@Override
public boolean areContentsTheSame(@NonNull Student oldItem, @NonNull Student newItem) {
return oldItem.equals(newItem);
}
};
protected RecyclerPagingAdapter() {
super(DIFF_STUDNET);
}
@NonNull
@Override
public MyRecyclerViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item, null);
return new MyRecyclerViewHolder(view);
}
@Override
public void onBindViewHolder(@NonNull MyRecyclerViewHolder holder, int position) {
Student student = getItem(position);
// item view 出来了, 分页库还在加载数据中,我就显示 Id加载中
if (null == student) {
holder.tvId.setText("Id加载中");
holder.tvName.setText("Name加载中");
holder.tvSex.setText("Sex加载中");
} else {
holder.tvId.setText(student.getId());
holder.tvName.setText(student.getName());
holder.tvSex.setText(student.getSex());
}
}
// Item 优化的 ViewHolder
public static class MyRecyclerViewHolder extends RecyclerView.ViewHolder {
TextView tvId;
TextView tvName;
TextView tvSex;
public MyRecyclerViewHolder(View itemView) {
super(itemView);
tvId = itemView.findViewById(R.id.tv_id); // ID
tvName = itemView.findViewById(R.id.tv_name); // 名称
tvSex = itemView.findViewById(R.id.tv_sex); // 性别
}
}
}
展示结果
public class MainActivity extends AppCompatActivity {
private RecyclerView recyclerView;
RecyclerPagingAdapter recyclerPagingAdapter;
StudentViewModel viewModel;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView = findViewById(R.id.recycle_view);
recyclerPagingAdapter = new RecyclerPagingAdapter();
// 最新版本初始化 viewModel
viewModel = new ViewModelProvider(this, new ViewModelProvider.NewInstanceFactory())
.get(StudentViewModel.class);
// LiveData 观察者 感应更新
viewModel.getListLiveData().observe(this, new Observer<PagedList<Student>>() {
@Override
public void onChanged(PagedList<Student> students) {
// 再这里更新适配器数据
recyclerPagingAdapter.submitList(students);
}
});
recyclerView.setAdapter(recyclerPagingAdapter);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
}
}
Paging的各个角色职责
- DataSource:数据的来源;
- DataSource.Factory:工厂类提供DataSource的实例,在自定义DataSource时使用;
- PagedList:数据集散中心,根据需要向DataSource索取加载数据,并将得到的数据传递到PagedListAdapter;
- PagedListAdapter:数据适配器,这里除了起到普通界面加载适配器的作用外,更重要的是根据滑动显示的坐标,起到了确定什么时候要求向PagedList加载数据;
- DiffUtil.ItemCallback:判断数据是否发生改变以确定界面是否更新;
数据源详解
DataSource是一个抽象类,但是我们不能直接继承它实现它的子类。但是Paging库里提供了它的三个子类供我们继承用于不同场景的实现:
第一种:PositionalDataSource:适用于目标数据总数固定,通过特定的位置加载数据,这里Key是Integer类型的位置信息,T即Value。 比如从数据库中的1200条开始加在20条数据。
第二种:ItemKeyedDataSource<Key, Value>:适用于目标数据的加载依赖特定item的信息, 即Key字段包含的是Item中的信息,比如需要根据第N项的信息加载第N+1项的数据,传参中需要传入第N项的ID时,该场景多出现于论坛类应用评论信息的请求。
第三种:PageKeyedDataSource<Key, Value>:适用于目标数据根据页信息请求数据的场景,即Key字段是页相关的信息。比如请求的数据的参数中包含类似next / pervious页数的信息。
Paging的源码分析
类之关系
abstract class DataSource<Key, Value>:
abstract class ItemKeyedDataSource<Key, Value>:
abstract class PageKeyedDataSource<Key, Value>:
abstract class PositionalDataSource: 我们刚刚使用的是这个 数据源子类
DataSource的三个子类:
PageKeyedDataSource:如果页面需要实现上一页、下一页,需要将请求的Token传递到下一步时使用 ItemKeyedDataSource:程序需要根据上一条数据信息(ID)获取下一条数据时使用 PositionalDataSource:需要从数据存储中选择的任何位置获取数据页;例如,请求可能返回以位置1200开头的20个数据项
当然是在拿取数据的地方开始分析,Paging组件的开始执行都是从创建 LiveData开始的,我们源码的分析也从LiveData的创建开始一探Paging背后的逻辑,我们开始分析吧:
初始化工作
开始查看 ”private final LiveData<PagedList> listLiveData;“ 此变量是如何创建的:
public StudentViewModel() {
StudentDataSourceFactory factory = new StudentDataSourceFactory();
this.listLiveData = new LivePagedListBuilder<Integer, Student>(factory, 20)
.build();
}
点击进入build函数分析:
@NonNull
@SuppressLint("RestrictedApi")
public LiveData<PagedList<Value>> build() {
return create(mInitialLoadKey, mConfig, mBoundaryCallback, mDataSourceFactory,
ArchTaskExecutor.getMainThreadExecutor(), mFetchExecutor);
}
进入create函数分析:
使用LivePagedListBuilder配置Factory和Config,然后调用build创建实例,在build方法中直接调用了create()方法创建LiveData
@AnyThread
@NonNull
private static <Key, Value> LiveData<PagedList<Value>> create(
@Nullable final Key initialLoadKey,
@NonNull final PagedList.Config config,
@Nullable final PagedList.BoundaryCallback boundaryCallback,
@NonNull final DataSource.Factory<Key, Value> dataSourceFactory,
@NonNull final Executor notifyExecutor,
@NonNull final Executor fetchExecutor) {
// 注意:在这里创建ComputableLiveData抽象类
return new ComputableLiveData<PagedList<Value>>(fetchExecutor) {
@Nullable
private PagedList<Value> mList;
@Nullable
private DataSource<Key, Value> mDataSource;
private final DataSource.InvalidatedCallback mCallback =
new DataSource.InvalidatedCallback() {
@Override
public void onInvalidated() {
invalidate();
}
};
// 注意,在这里重写compute方法, 是我们需要的PagedList<Value>
@Override
protected PagedList<Value> compute() {
@Nullable Key initializeKey = initialLoadKey;
if (mList != null) {
//noinspection unchecked
initializeKey = (Key) mList.getLastKey();
}
do {
if (mDataSource != null) {
mDataSource.removeInvalidatedCallback(mCallback);
}
// 从Builder中传入的Factory中创建DataSource
mDataSource = dataSourceFactory.create();
mDataSource.addInvalidatedCallback(mCallback);
// 创建PagedList
mList = new PagedList.Builder<>(mDataSource, config)
.setNotifyExecutor(notifyExecutor)
.setFetchExecutor(fetchExecutor)
.setBoundaryCallback(boundaryCallback)
.setInitialKey(initializeKey)
.build();
} while (mList.isDetached());
return mList;
}
}.getLiveData();
}
在create()中直接返回了ComputableLiveData的实例,在ComputableLiveData实例重写的compute中执行了一些主要操作:
一:调用传入的Factory的create()创建DataSource实例; 二:创建并返回PagedList实例; 三:PagedList.build() & PagedList.create() 就是如下代码(细节);
mList = new PagedList.Builder<>(mDataSource, config)
.setNotifyExecutor(notifyExecutor)
.setFetchExecutor(fetchExecutor)
.setBoundaryCallback(boundaryCallback)
.setInitialKey(initializeKey)
.build();
public PagedList<Value> build() {
// TODO: define defaults, once they can be used in module without android dependency
if (mNotifyExecutor == null) {
throw new IllegalArgumentException("MainThreadExecutor required");
}
if (mFetchExecutor == null) {
throw new IllegalArgumentException("BackgroundThreadExecutor required");
}
//noinspection unchecked
return PagedList.create(
mDataSource,
mNotifyExecutor,
mFetchExecutor,
mBoundaryCallback,
mConfig,
mInitialKey);
}
PagedList的创建过程,在PagedList.build()中调用了PagedList.create(),所以真正的创建是在create()中发生的:
private static <K, T> PagedList<T> create(...) {
if (dataSource.isContiguous() || !config.enablePlaceholders) {
......
return new ContiguousPagedList<>(contigDataSource,
notifyExecutor,
fetchExecutor,
boundaryCallback,
config,
key,
lastLoad);
} else {
return new TiledPagedList<>((PositionalDataSource<T>) dataSource,
notifyExecutor,
fetchExecutor,
boundaryCallback,
config,
(key != null) ? (Integer) key : 0);
}
}
从上面的代码中看出根据 条件(dataSource.isContiguous() || !config.enablePlaceholders)的不同分别创建ContiguousPagedList和TiledPagedList,其实这里就是区分上面的三个自定义DataSource的类型(三个数据源),如果是PositionalDataSource创建TiledPagedList,其他的返回ContiguousPagedList,我们依次查看三个DataSource中的isContiguous()方法:
PositionalDataSource类中的:
@Overrideboolean isContiguous() {
return false;
}
ItemKeyedDataSource和PageKeyedDataSource都继承与ContiguousDataSource,只查看ContiguousDataSource类中的:
@Overrideboolean isContiguous() {
return true;
}
又回来,从LivePageListBuilder .build开始看:
new ComputableLiveData
有什么用 与 何时执行compute函数, 这两个疑问,查看ComputableLiveData源码,发现在ComputableLiveData的构造函数中创建LiveData实例,下面查看Runnable接口中执行了哪些逻辑:
public ComputableLiveData(@NonNull Executor executor) {
mExecutor = executor;
mLiveData = new LiveData<T>() {
@Override
protected void onActive() {
mExecutor.execute(mRefreshRunnable);
}
};
}
final Runnable mRefreshRunnable = new Runnable() {
@WorkerThread
@Override
public void run() {
boolean computed;
do {
computed = false;
// compute can happen only in 1 thread but no reason to lock others.
if (mComputing.compareAndSet(false, true)) {
// as long as it is invalid, keep computing.
try {
T value = null;
while (mInvalid.compareAndSet(true, false)) {
computed = true;
// 这里会执行 compute(); 函数
// 调用了compuet创建了PagedList
value = compute();
}
if (computed) {
// 设置LiveData的值
mLiveData.postValue(value);
}
} finally {
// release compute lock
mComputing.set(false);
}
}
.......
} while (computed && mInvalid.get());
}
};
在mRefreshRunnable中调用了ComputableLiveData的compute()方法创建了PagedList,所以此处的Value就是PagedList,然后为mLiveData初始化赋值PagedList。
细心的会留意到,在上面的create()方法最后一句调用了getLiveData()获取到的就是ComputableLiveData构造函数中创建的LIveData:
@SuppressWarnings("WeakerAccess")
@NonNull
public LiveData<T> getLiveData() {
return mLiveData;
}
到这里为止,LiveData终于创建完成了
数据的加载工作
ContiguousPagedList 作为出发点
当我们自定义实现ItemKeySource时,创建的PagedList实际为ContiguousPagedList,查看ContiguousPagedList构造函数源码:
ContiguousPagedList(
@NonNull ContiguousDataSource<K, V> dataSource,
@NonNull Executor mainThreadExecutor, @NonNull Executor backgroundThreadExecutor,
@Nullable BoundaryCallback<V> boundaryCallback,
@NonNull Config config, final @Nullable K key, int lastLoad) {
super(new PagedStorage<V>(), mainThreadExecutor, backgroundThreadExecutor, boundaryCallback, config); mDataSource = dataSource;
mLastLoad = lastLoad;
if (mDataSource.isInvalid()) {
detach();
} else {
mDataSource.dispatchLoadInitial(key,mConfig.initialLoadSizeHint,mConfig.pageSize,
mConfig.enablePlaceholders,
mMainThreadExecutor,
mReceiver);
}
mShouldTrim = mDataSource.supportsPageDropping()&& mConfig.maxSize != Config.MAX_SIZE_UNBOUNDED;
}
ItermKeyDataSource的dispatchLoadInitial()
在构造函数中执行一下逻辑,所以继续追踪代码:
第一点:创建PagedStorage实例,主要根据滑动的位置显示是否要继续加载数据
第二点:调用DataSource.dispatchLoadInitial方法,此时使用的时ItermKeyDataSource的dispatchLoadInitial 方法
@Override
final void dispatchLoadInitial(@Nullable Key key, int initialLoadSize, int pageSize,
boolean enablePlaceholders,
@NonNull Executor mainThreadExecutor,
@NonNull PageResult.Receiver<Value> receiver) {
LoadInitialCallbackImpl<Value> callback = new LoadInitialCallbackImpl<>(this, enablePlaceholders, receiver); loadInitial(new LoadInitialParams<>(key, initialLoadSize, enablePlaceholders), callback);
callback.mCallbackHelper.setPostExecutor(mainThreadExecutor);
}
上面代码在ItermKeyDataSource的dispatchLoadInitial()方法中调用了抽象函数loadInitial(),根据前面的学习我们知道在 loadInitial() 中设置了初始化的网络请求,到此实现了Paging组件初始化数据的加载
数据的显示工作
在自定义ItemDataSource的loadInitial()中加载数据后,调用了callback.onResult(it?.data!!.datas!!)方法,此处的callback是LoadInitialCallback的实现类LoadInitialCallbackImpl,在onResult()方法中又调用了LoadCallbackHelper.dispatchResultToReceiver()
static class LoadInitialCallbackImpl<Key, Value> extends LoadInitialCallback<Key, Value> {
final LoadCallbackHelper<Value> mCallbackHelper;
private final PageKeyedDataSource<Key, Value> mDataSource;
private final boolean mCountingEnabled;
LoadInitialCallbackImpl(@NonNull PageKeyedDataSource<Key, Value> dataSource,
boolean countingEnabled, @NonNull PageResult.Receiver<Value> receiver) {
mCallbackHelper = new LoadCallbackHelper<>(
dataSource, PageResult.INIT, null, receiver);
mDataSource = dataSource;
mCountingEnabled = countingEnabled;
}
@Override
public void onResult(@NonNull List<Value> data, @Nullable Key previousPageKey,
@Nullable Key nextPageKey) {
if (!mCallbackHelper.dispatchInvalidResultIfInvalid()) {
mDataSource.initKeys(previousPageKey, nextPageKey);
mCallbackHelper.dispatchResultToReceiver(new PageResult<>(data, 0, 0, 0));
}
}
狙击点:LoadCallbackHelper.dispatchResultToReceiver()
void dispatchResultToReceiver(final @NonNull PageResult<T> result) {
Executor executor;
synchronized (mSignalLock) {
if (mHasSignalled) {
throw new IllegalStateException(
"callback.onResult already called, cannot call again.");
}
mHasSignalled = true;
executor = mPostExecutor;
}
if (executor != null) {
executor.execute(new Runnable() {
@Override
public void run() {
mReceiver.onPageResult(mResultType, result);
}
});
} else {
mReceiver.onPageResult(mResultType, result);
}
}
在dispatchResultToReceiver()方法中,调用PageResult.Receiver.onPageResult()方法,这里的mReceiver是在调用mDataSource.dispatchLoadInitial()时传入的最后一个参数,他的实现在ContiguousPagedList中匿名创建:
final PageResult.Receiver<T> mReceiver; // mSignalLock protects mPostExecutor, and mHasSignalled
private final Object mSignalLock = new Object();
private Executor mPostExecutor = null;
private boolean mHasSignalled = false;
LoadCallbackHelper(@NonNull DataSource dataSource, @PageResult.ResultType int resultType,
@Nullable Executor mainThreadExecutor, @NonNull PageResult.Receiver<T> receiver) {
mDataSource = dataSource;
mResultType = resultType;
mPostExecutor = mainThreadExecutor;
mReceiver = receiver;
}
ContiguousPagedList:
private PageResult.Receiver<V> mReceiver = new PageResult.Receiver<V>() {
// Creation thread for initial synchronous load, otherwise main thread
// Safe to access main thread only state - no other thread has reference during construction
@AnyThread
@Override
public void onPageResult(@PageResult.ResultType int resultType,
@NonNull PageResult<V> pageResult) {
List<V> page = pageResult.page;
if (resultType == PageResult.INIT) {
mStorage.init(pageResult.leadingNulls, page, pageResult.trailingNulls,
pageResult.positionOffset, ContiguousPagedList.this);
if (mLastLoad == LAST_LOAD_UNSPECIFIED) {
// Because the ContiguousPagedList wasn't initialized with a last load position,
// initialize it to the middle of the initial load
mLastLoad =
pageResult.leadingNulls + pageResult.positionOffset + page.size() / 2;
}
} else if (resultType == PageResult.APPEND) {
mStorage.appendPage(page, ContiguousPagedList.this);
} else if (resultType == PageResult.PREPEND) {
mStorage.prependPage(page, ContiguousPagedList.this);
} else {
throw new IllegalArgumentException("unexpected resultType " + resultType);
}
}
}
};
在onPageResult()方法中根据resultType的类型执行操作,PageResult的三个数据类型分别对应者ItemKeyDataSource的三个方法:
loadInitial:对应初始化状态PageResult.INIT loadBefore:对应初始化状态PageResult.PREPEND loadAfter:对应初始化状态PageResult.APPEND
此出分析初始化,回调的类型为PageResult.INIT,调用了PagedStorage的init()方法:
mStorage.init(pageResult.leadingNulls, page, pageResult.trailingNulls,
pageResult.positionOffset, ContiguousPagedList.this);
void init(int leadingNulls,
@NonNull List<T> page, int trailingNulls, int positionOffset,
@NonNull Callback callback) {
init(leadingNulls, page, trailingNulls, positionOffset);
callback.onInitialized(size());
}
在init()方法中首先调用另一个init()方法记录加载的位置,并保存加载的数据, 然后调用callback.onInitialized(),在onInitialzed()方法中调用了notifyInserted(),在notifyInserted()中遍历mCallbacks回调callback的onInserted()
interface Callback {
void onInitialized(int count);
void onPagePrepended(int leadingNulls, int changed, int added);
void onPageAppended(int endPosition, int changed, int added);
void onPagePlaceholderInserted(int pageIndex);
void onPageInserted(int start, int count);
void onPagesRemoved(int startOfDrops, int count);
void onPagesSwappedToPlaceholder(int startOfDrops, int count);
void onEmptyPrepend();
void onEmptyAppend();
}
继续追踪源码:
//ContiguousPagedList:
public void onInitialized(int count) {
notifyInserted(0, count);
}
PagedList:
void notifyInserted(int position, int count) {
if (count != 0) {
for (int i = mCallbacks.size() - 1; i >= 0; i--) {
Callback callback = mCallbacks.get(i).get();
if (callback != null) {
callback.onInserted(position, count);
}
}
}
}
//PagedList 的 接口:public abstract void onInserted(int position, int count);
以上源码, 让我们明白了:
一: 加载的数据保存在PagedStorage中,并记录了加载的位置信息
二: 加载完成后根据数据的变化,回调callback.onInserted()通知数据改变的数量和位置
终于看到曙光了:
那CallBack是从哪来的呢?应该是哪里需要哪里才会注册回调,想想数据位置的变化在哪个地方能用得着,哪个地方优惠根据position和count处理呢?答案就在PagedListAdapter中 终于要看到 PagedListAdapter 了
PagedListAdapter
当然 下面我们也可以简单的追踪下代码 能否到 PagedListAdapter
AsyncPagedListDiffer:
public AsyncPagedListDiffer(@NonNull ListUpdateCallback listUpdateCallback, @NonNull AsyncDifferConfig<T> config) {
class NamelessClass_1 extends Callback {
NamelessClass_1() {
}
public void onInserted(int position, int count) {
AsyncPagedListDiffer.this.mUpdateCallback.onInserted(position, count);
}
public void onRemoved(int position, int count) {
AsyncPagedListDiffer.this.mUpdateCallback.onRemoved(position, count);
}
public void onChanged(int position, int count) {
AsyncPagedListDiffer.this.mUpdateCallback.onChanged(position, count, (Object)null);
}
}
ListUpdateCallback:
public interface ListUpdateCallback {
......
void onInserted(int position, int count);
}
AdapterListUpdateCallback:
@Overridepublic void onInserted(int position, int count) {
mAdapter.notifyItemRangeInserted(position, count);
}
逆向方式,自己去看文字
逆向源码收尾:
在我们开始写的使用Paging的实例中,使用submitList()设置数据,而submiList()直接调用了mDiffer.submitList(pagedList):
public void submitList(PagedList<T> pagedList) {
mDiffer.submitList(pagedList);
}
public void submitList(final PagedList<T> pagedList) {
if (mPagedList == null && mSnapshot == null) {
// fast simple first insert
mPagedList = pagedList;
pagedList.addWeakCallback(null, mPagedListCallback);
return;
}
}
这里就调用了addWeakCallback()添加Callback实例mPagedListCallback
private PagedList.Callback mPagedListCallback = new PagedList.Callback() {
@Override
public void onInserted(int position, int count) {
mUpdateCallback.onInserted(position, count);
}
@Override
public void onRemoved(int position, int count) {
mUpdateCallback.onRemoved(position, count);
}
@Override
public void onChanged(int position, int count) {
// NOTE: pass a null payload to convey null -> item
mUpdateCallback.onChanged(position, count, null);
}
};
上面源码中, mPagedListCallback的onInserted()直接回调mUPdateCallback.onInserted(),这里的mUPdateCallback正是在PagedListAdapter的构造函数中创建Differ,而在AsyncPagedListDiffer的构造函数中直接初始化了AdapterListUpdateCallback对象
public AsyncPagedListDiffer(@NonNull RecyclerView.Adapter adapter,
@NonNull DiffUtil.ItemCallback<T> diffCallback) {
mUpdateCallback = new AdapterListUpdateCallback(adapter);
mConfig = new AsyncDifferConfig.Builder<T>(diffCallback).build();
}
所以程序执行到AdapterListUpdateCallback中,在AdapterListUpdateCallback.onInserted()中直接调用传入的Adapter的notifyItemRangeInserted(position, count)实现数据更新,这里的Adapter就是