/*
* Copyright 2021 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 androidx.appsearch.debugview.view;
import androidx.annotation.NonNull;
import androidx.annotation.RestrictTo;
import androidx.core.util.Preconditions;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
/**
* Listens for scrolling and loads the next page of results if the end of the view is reached.
*
* @hide
*/
@RestrictTo(RestrictTo.Scope.LIBRARY)
public abstract class ScrollListener extends RecyclerView.OnScrollListener {
private final LinearLayoutManager mLayoutManager;
public ScrollListener(@NonNull LinearLayoutManager layoutManager) {
mLayoutManager = Preconditions.checkNotNull(layoutManager);
}
@Override
public void onScrolled(@NonNull RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
int itemsVisible = mLayoutManager.getChildCount();
int totalItems = mLayoutManager.getItemCount();
int firstItemInViewIndex = mLayoutManager.findFirstVisibleItemPosition();
// This value is true when the RecyclerView has additional rows that can be filled and
// the underlying adapter does not have sufficient items to fill them.
boolean hasAdditionalRowsToFill = (firstItemInViewIndex + itemsVisible) >= totalItems;
if (!isLoading() && hasAdditionalPages()) {
if (hasAdditionalRowsToFill && firstItemInViewIndex >= 0) {
loadNextPage();
}
}
}
/**
* Defines how to load the next page of results to display.
*/
public abstract void loadNextPage();
/**
* Indicates whether a page is currently be loading.
*
* <p>{@link #loadNextPage()} will not be called if this is {@code true}.
*/
public abstract boolean isLoading();
/**
* Indicates whether there are additional pages to load.
*
* <p>{@link #loadNextPage()} will not be called if this is {@code true}.
*/
public abstract boolean hasAdditionalPages();
}