ViewportHint.kt
/*
* Copyright 2019 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.paging
import androidx.paging.PagingSource.LoadResult.Page
/**
* Load access information blob, containing information from presenter.
*/
internal sealed class ViewportHint(
/**
* Distance from hint to first loaded item: `anchorPosition - firstLoadedItemPosition`
*
* Zero indicates access at boundary
* Positive -> Within loaded range or in placeholders if greater than size of last page.
* Negative -> placeholder access.
*
* Note: Does not include placeholders.
*/
val presentedItemsBefore: Int,
/**
* Distance from hint to last presented item: `size - index - placeholdersAfter - 1`
*
* Zero indicates access at boundary
* Positive -> Within loaded range or in placeholders if greater than size of last page.
* Negative -> placeholder access.
*
* Note: Does not include placeholders.
*/
val presentedItemsAfter: Int,
/**
* [hintOriginalPageOffset][TransformablePage.hintOriginalPageOffset] of the first presented
* [TransformablePage] when this [ViewportHint] was created.
*/
val originalPageOffsetFirst: Int,
/**
* [hintOriginalPageOffset][TransformablePage.hintOriginalPageOffset] of the last presented
* [TransformablePage] when this [ViewportHint] was created.
*/
val originalPageOffsetLast: Int,
) {
override fun equals(other: Any?): Boolean {
if (this === other) return true
if (other !is ViewportHint) return false
return presentedItemsBefore == other.presentedItemsBefore &&
presentedItemsAfter == other.presentedItemsAfter &&
originalPageOffsetFirst == other.originalPageOffsetFirst &&
originalPageOffsetLast == other.originalPageOffsetLast
}
override fun hashCode(): Int {
return presentedItemsBefore.hashCode() + presentedItemsAfter.hashCode() +
originalPageOffsetFirst.hashCode() + originalPageOffsetLast.hashCode()
}
/**
* [ViewportHint] reporting presenter state after receiving initial page. An [Initial] hint
* should never take precedence over an [Access] hint and is only used to inform
* [PageFetcher] how many items from the initial page load were presented by [PagingDataDiffer]
*/
class Initial(
presentedItemsBefore: Int,
presentedItemsAfter: Int,
originalPageOffsetFirst: Int,
originalPageOffsetLast: Int
) : ViewportHint(
presentedItemsBefore = presentedItemsBefore,
presentedItemsAfter = presentedItemsAfter,
originalPageOffsetFirst = originalPageOffsetFirst,
originalPageOffsetLast = originalPageOffsetLast,
) {
override fun toString(): String {
return """ViewportHint.Initial(
| presentedItemsBefore=$presentedItemsBefore,
| presentedItemsAfter=$presentedItemsAfter,
| originalPageOffsetFirst=$originalPageOffsetFirst,
| originalPageOffsetLast=$originalPageOffsetLast,
|)""".trimMargin()
}
}
/**
* [ViewportHint] representing an item access that should be used to trigger loads to fulfill
* prefetch distance.
*/
class Access(
/**
* Page index offset from initial load
*/
val pageOffset: Int,
/**
* Original index of item in the [Page] with [pageOffset].
*
* Three cases to consider:
* - [indexInPage] in Page.data.indices -> Hint references original item directly
* - [indexInPage] > Page.data.indices -> Hint references a placeholder after the last
* presented item.
* - [indexInPage] < 0 -> Hint references a placeholder before the first presented item.
*/
val indexInPage: Int,
presentedItemsBefore: Int,
presentedItemsAfter: Int,
originalPageOffsetFirst: Int,
originalPageOffsetLast: Int
) : ViewportHint(
presentedItemsBefore = presentedItemsBefore,
presentedItemsAfter = presentedItemsAfter,
originalPageOffsetFirst = originalPageOffsetFirst,
originalPageOffsetLast = originalPageOffsetLast,
) {
override fun equals(other: Any?): Boolean {
if (this === other) return true
if (other !is Access) return false
return pageOffset == other.pageOffset &&
indexInPage == other.indexInPage &&
presentedItemsBefore == other.presentedItemsBefore &&
presentedItemsAfter == other.presentedItemsAfter &&
originalPageOffsetFirst == other.originalPageOffsetFirst &&
originalPageOffsetLast == other.originalPageOffsetLast
}
override fun hashCode(): Int {
return super.hashCode() + pageOffset.hashCode() + indexInPage.hashCode()
}
override fun toString(): String {
return """ViewportHint.Access(
| pageOffset=$pageOffset,
| indexInPage=$indexInPage,
| presentedItemsBefore=$presentedItemsBefore,
| presentedItemsAfter=$presentedItemsAfter,
| originalPageOffsetFirst=$originalPageOffsetFirst,
| originalPageOffsetLast=$originalPageOffsetLast,
|)""".trimMargin()
}
}
}