# SnapshotLoader # SnapshotLoader Artifact:[androidx.paging:paging-testing](https://developer.android.com/jetpack/androidx/releases/paging) [View Source](https://cs.android.com/search?q=file:androidx/paging/testing/SnapshotLoader.kt+class:androidx.paging.testing.SnapshotLoader) Added in[3.2.0](https://developer.android.com/jetpack/androidx/releases/paging#3.2.0) *** ** * ** *** Kotlin\|[Java](https://developer.android.com/reference/androidx/paging/testing/SnapshotLoader "View this page in Java") Common/All - Cmn ``` @VisibleForTesting class SnapshotLoader ``` *** ** * ** *** Contains the public APIs for load operations in tests. Tracks generational information and provides the listener to[LoaderCallback](https://developer.android.com/reference/kotlin/androidx/paging/testing/LoaderCallback)on[PagingDataPresenter](https://developer.android.com/reference/kotlin/androidx/paging/PagingDataPresenter)operations. ## Summary | ### Public functions | |-----------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-----| | `suspend `[Unit](https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-unit/index.html) | [appendScrollWhile](https://developer.android.com/reference/kotlin/androidx/paging/testing/SnapshotLoader#appendScrollWhile(kotlin.Function1))`(predicate: (item) `->` `[Boolean](https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-boolean/index.html)`)` Imitates scrolling down paged items,[appending](https://developer.android.com/reference/kotlin/androidx/paging/LoadType#APPEND)data until the given predicate returns false. | Cmn | | `suspend `[Unit](https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-unit/index.html) | [flingTo](https://developer.android.com/reference/kotlin/androidx/paging/testing/SnapshotLoader#flingTo(kotlin.Int))`(index: `[Int](https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-int/index.html)`)` Imitates flinging from current index to the target index. | Cmn | | `suspend `[Unit](https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-unit/index.html) | [prependScrollWhile](https://developer.android.com/reference/kotlin/androidx/paging/testing/SnapshotLoader#prependScrollWhile(kotlin.Function1))`(predicate: (item) `->` `[Boolean](https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-boolean/index.html)`)` Imitates scrolling up paged items,[prepending](https://developer.android.com/reference/kotlin/androidx/paging/LoadType#PREPEND)data until the given predicate returns false. | Cmn | | `suspend `[Unit](https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-unit/index.html) | [refresh](https://developer.android.com/reference/kotlin/androidx/paging/testing/SnapshotLoader#refresh())`()` Refresh the data that is presented on the UI. | Cmn | | `suspend `[Unit](https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-unit/index.html) | [scrollTo](https://developer.android.com/reference/kotlin/androidx/paging/testing/SnapshotLoader#scrollTo(kotlin.Int))`(index: `[Int](https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-int/index.html)`)` Imitates scrolling from current index to the target index. | Cmn | ## Public functions ### appendScrollWhile Cmn ``` suspend fun appendScrollWhile(predicate: (item) -> Boolean): Unit ``` Imitates scrolling down paged items,[appending](https://developer.android.com/reference/kotlin/androidx/paging/LoadType#APPEND)data until the given predicate returns false. Note: This API loads an item before passing it into the predicate. This means the loaded pages may include the page which contains the item that does not match the predicate. For example, if pageSize = 2, the predicate {item: Int -\> item \< 3 } will return items \[1, 2,3, 4\] where 3, 4 is the page containing the boundary item3 not matching the predicate. The loaded pages are also dependent on[PagingConfig](https://developer.android.com/reference/kotlin/androidx/paging/PagingConfig)settings such as[PagingConfig.prefetchDistance](https://developer.android.com/reference/kotlin/androidx/paging/PagingConfig#prefetchDistance()): - if`prefetchDistance`0, the resulting appends will include prefetched items. For example, if pageSize = 2 and prefetchDistance = 2, the predicate {item: Int -\> item \< 3 } will load items \[1, 2, 3, 4, 5, 6\] where 5, 6 is the prefetched page. | Parameters | |--------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------| | `predicate: (item) `->` `[Boolean](https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-boolean/index.html) | the predicate to match (return true) to continue append scrolls | ### flingTo Cmn ``` suspend fun flingTo(index: Int): Unit ``` Imitates flinging from current index to the target index. It will continue scrolling even as data is being loaded in. Returns all available data that has been scrolled through. The scroll direction (prepend or append) is dependent on current index and target index. In general, scrolling to a smaller index triggers[PREPEND](https://developer.android.com/reference/kotlin/androidx/paging/LoadType#PREPEND)while scrolling to a larger index triggers[APPEND](https://developer.android.com/reference/kotlin/androidx/paging/LoadType#APPEND). This function will scroll into placeholders. This means jumping is supported when[PagingConfig.enablePlaceholders](https://developer.android.com/reference/kotlin/androidx/paging/PagingConfig#enablePlaceholders())is true and the amount of placeholders traversed has reached[PagingConfig.jumpThreshold](https://developer.android.com/reference/kotlin/androidx/paging/PagingConfig#jumpThreshold()). Jumping is disabled when[PagingConfig.enablePlaceholders](https://developer.android.com/reference/kotlin/androidx/paging/PagingConfig#enablePlaceholders())is false. When[PagingConfig.enablePlaceholders](https://developer.android.com/reference/kotlin/androidx/paging/PagingConfig#enablePlaceholders())is false, the[index](https://developer.android.com/reference/kotlin/androidx/paging/testing/SnapshotLoader#flingTo(kotlin.Int))is scoped within currently loaded items. For example, in a list of items(0-20) with currently loaded items(10-15), index0 = item(10), index4 = item(15). Supports[index](https://developer.android.com/reference/kotlin/androidx/paging/testing/SnapshotLoader#flingTo(kotlin.Int))beyond currently loaded items when[PagingConfig.enablePlaceholders](https://developer.android.com/reference/kotlin/androidx/paging/PagingConfig#enablePlaceholders())is false: 1. For prepends, it supports negative indices for as long as there are still available data to load from. For example, take a list of items(0-20), pageSize = 1, with currently loaded items(10-15). With index0 = item(10), a`scrollTo(-4)`will scroll to item(6) and update index0 = item(6). 2. For appends, it supports indices \>= loadedDataSize. For example, take a list of items(0-20), pageSize = 1, with currently loaded items(10-15). With index4 = item(15), a`scrollTo(7)`will scroll to item(18) and update index7 = item(18). Note that both examples does not account for prefetches. The[index](https://developer.android.com/reference/kotlin/androidx/paging/testing/SnapshotLoader#flingTo(kotlin.Int))accounts for separators/headers/footers where each one of those consumes one scrolled index. For both append/prepend, this function stops loading prior to fulfilling requested scroll distance if there are no more data to load from. | Parameters | |--------------------------------------------------------------------------------------|-------------------------------| | `index: `[Int](https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-int/index.html) | The target index to scroll to | | See also | |------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------| | [scrollTo](https://developer.android.com/reference/kotlin/androidx/paging/testing/SnapshotLoader#scrollTo(kotlin.Int)) | for faking scrolls that awaits for placeholders to load before continuing to scroll. | ### prependScrollWhile Cmn ``` suspend fun prependScrollWhile(predicate: (item) -> Boolean): Unit ``` Imitates scrolling up paged items,[prepending](https://developer.android.com/reference/kotlin/androidx/paging/LoadType#PREPEND)data until the given predicate returns false. Note: This API loads an item before passing it into the predicate. This means the loaded pages may include the page which contains the item that does not match the predicate. For example, if pageSize = 2, initialKey = 3, the predicate {item: Int -\> item \>= 3 } will return items \[1, 2,3, 4\] where 1, 2 is the page containing the boundary item2 not matching the predicate. The loaded pages are also dependent on[PagingConfig](https://developer.android.com/reference/kotlin/androidx/paging/PagingConfig)settings such as[PagingConfig.prefetchDistance](https://developer.android.com/reference/kotlin/androidx/paging/PagingConfig#prefetchDistance()): - if`prefetchDistance`0, the resulting prepends will include prefetched items. For example, if pageSize = 2, initialKey = 3, and prefetchDistance = 2, the predicate {item: Int -\> item 4 } will load items \[1, 2, 3, 4, 5, 6\] where both 1,2 and 5, 6 are the prefetched pages. | Parameters | |--------------------------------------------------------------------------------------------------------------|------------------------------------------------------------------| | `predicate: (item) `->` `[Boolean](https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-boolean/index.html) | the predicate to match (return true) to continue prepend scrolls | ### refresh Cmn ``` suspend fun refresh(): Unit ``` Refresh the data that is presented on the UI. [refresh](https://developer.android.com/reference/kotlin/androidx/paging/testing/SnapshotLoader#refresh())triggers a new generation of[PagingData](https://developer.android.com/reference/kotlin/androidx/paging/PagingData)/[PagingSource](https://developer.android.com/reference/kotlin/androidx/paging/PagingSource)to represent an updated snapshot of the backing dataset. This fake paging operation mimics UI-driven refresh signals such as swipe-to-refresh. ### scrollTo Cmn ``` suspend fun scrollTo(index: Int): Unit ``` Imitates scrolling from current index to the target index. It waits for an item to be loaded in before triggering load on next item. Returns all available data that has been scrolled through. The scroll direction (prepend or append) is dependent on current index and target index. In general, scrolling to a smaller index triggers[PREPEND](https://developer.android.com/reference/kotlin/androidx/paging/LoadType#PREPEND)while scrolling to a larger index triggers[APPEND](https://developer.android.com/reference/kotlin/androidx/paging/LoadType#APPEND). When[PagingConfig.enablePlaceholders](https://developer.android.com/reference/kotlin/androidx/paging/PagingConfig#enablePlaceholders())is false, the[index](https://developer.android.com/reference/kotlin/androidx/paging/testing/SnapshotLoader#scrollTo(kotlin.Int))is scoped within currently loaded items. For example, in a list of items(0-20) with currently loaded items(10-15), index0 = item(10), index4 = item(15). Supports[index](https://developer.android.com/reference/kotlin/androidx/paging/testing/SnapshotLoader#scrollTo(kotlin.Int))beyond currently loaded items when[PagingConfig.enablePlaceholders](https://developer.android.com/reference/kotlin/androidx/paging/PagingConfig#enablePlaceholders())is false: 1. For prepends, it supports negative indices for as long as there are still available data to load from. For example, take a list of items(0-20), pageSize = 1, with currently loaded items(10-15). With index0 = item(10), a`scrollTo(-4)`will scroll to item(6) and update index0 = item(6). 2. For appends, it supports indices \>= loadedDataSize. For example, take a list of items(0-20), pageSize = 1, with currently loaded items(10-15). With index4 = item(15), a`scrollTo(7)`will scroll to item(18) and update index7 = item(18). Note that both examples does not account for prefetches. The[index](https://developer.android.com/reference/kotlin/androidx/paging/testing/SnapshotLoader#scrollTo(kotlin.Int))accounts for separators/headers/footers where each one of those consumes one scrolled index. For both append/prepend, this function stops loading prior to fulfilling requested scroll distance if there are no more data to load from. | Parameters | |--------------------------------------------------------------------------------------|-------------------------------| | `index: `[Int](https://kotlinlang.org/api/core/kotlin-stdlib/kotlin/-int/index.html) | The target index to scroll to | | See also | |----------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------| | [flingTo](https://developer.android.com/reference/kotlin/androidx/paging/testing/SnapshotLoader#flingTo(kotlin.Int)) | for faking a scroll that continues scrolling without waiting for items to be loaded in. Supports jumping. |