Merge pull request #810 from chrisbanes/cb/snapper-migration

Migrate Pager to use Snapper

gradle/libs.versions.toml

@@ -27,6 +27,8 @@ compose-material-material = { module = "androidx.compose.material:material", ver
 compose-material-iconsext = { module = "androidx.compose.material:material-icons-extended", version.ref = "compose" }
 compose-animation-animation = { module = "androidx.compose.animation:animation", version.ref = "compose" }
 
+snapper = "dev.chrisbanes.snapper:snapper:0.1.0"
+
 android-gradlePlugin = { module = "com.android.tools.build:gradle", version.ref = "gradlePlugin" }
 gradleMavenPublishPlugin = "com.vanniktech:gradle-maven-publish-plugin:0.17.0"
 metalavaGradle = "me.tylerbwong.gradle:metalava-gradle:0.1.9"

pager/api/current.api

@@ -5,14 +5,15 @@ package com.google.accompanist.pager {
   }
 
   public final class Pager {
-    method @androidx.compose.runtime.Composable @com.google.accompanist.pager.ExperimentalPagerApi public static void HorizontalPager(int count, optional androidx.compose.ui.Modifier modifier, optional com.google.accompanist.pager.PagerState state, optional boolean reverseLayout, optional float itemSpacing, optional androidx.compose.foundation.gestures.FlingBehavior flingBehavior, optional androidx.compose.ui.Alignment.Vertical verticalAlignment, optional kotlin.jvm.functions.Function1<? super java.lang.Integer,?>? key, optional androidx.compose.foundation.layout.PaddingValues contentPadding, kotlin.jvm.functions.Function2<? super com.google.accompanist.pager.PagerScope,? super java.lang.Integer,kotlin.Unit> content);
-    method @androidx.compose.runtime.Composable @com.google.accompanist.pager.ExperimentalPagerApi public static void VerticalPager(int count, optional androidx.compose.ui.Modifier modifier, optional com.google.accompanist.pager.PagerState state, optional boolean reverseLayout, optional float itemSpacing, optional androidx.compose.foundation.gestures.FlingBehavior flingBehavior, optional androidx.compose.ui.Alignment.Horizontal horizontalAlignment, optional kotlin.jvm.functions.Function1<? super java.lang.Integer,?>? key, optional androidx.compose.foundation.layout.PaddingValues contentPadding, kotlin.jvm.functions.Function2<? super com.google.accompanist.pager.PagerScope,? super java.lang.Integer,kotlin.Unit> content);
+    method @androidx.compose.runtime.Composable @com.google.accompanist.pager.ExperimentalPagerApi public static void HorizontalPager(int count, optional androidx.compose.ui.Modifier modifier, optional com.google.accompanist.pager.PagerState state, optional boolean reverseLayout, optional float itemSpacing, optional androidx.compose.foundation.layout.PaddingValues contentPadding, optional androidx.compose.ui.Alignment.Vertical verticalAlignment, optional androidx.compose.foundation.gestures.FlingBehavior flingBehavior, optional kotlin.jvm.functions.Function1<? super java.lang.Integer,?>? key, kotlin.jvm.functions.Function2<? super com.google.accompanist.pager.PagerScope,? super java.lang.Integer,kotlin.Unit> content);
+    method @androidx.compose.runtime.Composable @com.google.accompanist.pager.ExperimentalPagerApi public static void VerticalPager(int count, optional androidx.compose.ui.Modifier modifier, optional com.google.accompanist.pager.PagerState state, optional boolean reverseLayout, optional float itemSpacing, optional androidx.compose.foundation.layout.PaddingValues contentPadding, optional androidx.compose.ui.Alignment.Horizontal horizontalAlignment, optional androidx.compose.foundation.gestures.FlingBehavior flingBehavior, optional kotlin.jvm.functions.Function1<? super java.lang.Integer,?>? key, kotlin.jvm.functions.Function2<? super com.google.accompanist.pager.PagerScope,? super java.lang.Integer,kotlin.Unit> content);
     method @com.google.accompanist.pager.ExperimentalPagerApi public static float calculateCurrentOffsetForPage(com.google.accompanist.pager.PagerScope, int page);
   }
 
   @com.google.accompanist.pager.ExperimentalPagerApi public final class PagerDefaults {
-    method @androidx.compose.runtime.Composable public androidx.compose.foundation.gestures.FlingBehavior flingBehavior(com.google.accompanist.pager.PagerState state, optional androidx.compose.animation.core.DecayAnimationSpec<java.lang.Float> decayAnimationSpec, optional androidx.compose.animation.core.AnimationSpec<java.lang.Float> snapAnimationSpec);
-    method @Deprecated @androidx.compose.runtime.Composable public androidx.compose.foundation.gestures.FlingBehavior rememberPagerFlingConfig(com.google.accompanist.pager.PagerState state, optional androidx.compose.animation.core.DecayAnimationSpec<java.lang.Float> decayAnimationSpec, optional androidx.compose.animation.core.AnimationSpec<java.lang.Float> snapAnimationSpec);
+    method @androidx.compose.runtime.Composable @dev.chrisbanes.snapper.ExperimentalSnapperApi public androidx.compose.foundation.gestures.FlingBehavior flingBehavior(com.google.accompanist.pager.PagerState state, optional androidx.compose.animation.core.DecayAnimationSpec<java.lang.Float> decayAnimationSpec, optional androidx.compose.animation.core.AnimationSpec<java.lang.Float> snapAnimationSpec, optional kotlin.jvm.functions.Function1<? super dev.chrisbanes.snapper.SnapperLayoutInfo,java.lang.Float> maximumFlingDistance, optional float endContentPadding);
+    method public kotlin.jvm.functions.Function1<dev.chrisbanes.snapper.SnapperLayoutInfo,java.lang.Float> getSinglePageFlingDistance();
+    property public final kotlin.jvm.functions.Function1<dev.chrisbanes.snapper.SnapperLayoutInfo,java.lang.Float> singlePageFlingDistance;
     field public static final com.google.accompanist.pager.PagerDefaults INSTANCE;
   }
 
@@ -51,12 +52,8 @@ package com.google.accompanist.pager {
   }
 
   public final class PagerStateKt {
-    method @Deprecated @androidx.compose.runtime.Composable @com.google.accompanist.pager.ExperimentalPagerApi public static inline com.google.accompanist.pager.PagerState rememberPagerState(@IntRange(from=0) int pageCount, optional @IntRange(from=0) int initialPage, optional @FloatRange(from=0.0, to=1.0) float initialPageOffset, optional @IntRange(from=1) int initialOffscreenLimit, optional boolean infiniteLoop);
     method @androidx.compose.runtime.Composable @com.google.accompanist.pager.ExperimentalPagerApi public static com.google.accompanist.pager.PagerState rememberPagerState(optional @IntRange(from=0) int initialPage);
   }
 
-  public final class SnappingFlingBehaviorKt {
-  }
-
 }
 

pager/build.gradle

@@ -82,7 +82,9 @@ android {
 }
 
 dependencies {
-    implementation libs.compose.foundation.foundation
+    api libs.compose.foundation.foundation
+    api libs.snapper
+
     implementation libs.napier
 
     // ======================

pager/src/androidTest/kotlin/com/google/accompanist/pager/InstrumentedHorizontalPagerTest.kt

@@ -55,6 +55,7 @@ class InstrumentedHorizontalPagerTest(
             .combineWithParameters(1f)
             // contentPadding
             .combineWithParameters(
+                PaddingValues(horizontal = 0.dp), // Fill
                 PaddingValues(end = 32.dp), // Alignment.Start
                 PaddingValues(horizontal = 32.dp), // Alignment.Center
                 PaddingValues(start = 32.dp), // Alignment.End

pager/src/androidTest/kotlin/com/google/accompanist/pager/InstrumentedVerticalPagerTest.kt

@@ -49,6 +49,7 @@ class InstrumentedVerticalPagerTest(
         fun data() = parameterizedParams()
             // contentPadding
             .combineWithParameters(
+                PaddingValues(vertical = 0.dp), // Fill
                 PaddingValues(bottom = 32.dp), // Alignment.Top
                 PaddingValues(vertical = 32.dp), // Alignment.Center
                 PaddingValues(top = 32.dp), // Alignment.Bottom

pager/src/main/java/com/google/accompanist/pager/Pager.kt

@@ -25,6 +25,7 @@ import androidx.compose.foundation.gestures.FlingBehavior
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.PaddingValues
+import androidx.compose.foundation.layout.calculateEndPadding
 import androidx.compose.foundation.layout.wrapContentSize
 import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.foundation.lazy.LazyRow
@@ -40,8 +41,15 @@ import androidx.compose.ui.input.nestedscroll.NestedScrollConnection
 import androidx.compose.ui.input.nestedscroll.NestedScrollSource
 import androidx.compose.ui.input.nestedscroll.nestedScroll
 import androidx.compose.ui.unit.Dp
+import androidx.compose.ui.unit.LayoutDirection
 import androidx.compose.ui.unit.Velocity
 import androidx.compose.ui.unit.dp
+import dev.chrisbanes.snapper.ExperimentalSnapperApi
+import dev.chrisbanes.snapper.SnapOffsets
+import dev.chrisbanes.snapper.SnapperFlingBehavior
+import dev.chrisbanes.snapper.SnapperFlingBehaviorDefaults
+import dev.chrisbanes.snapper.SnapperLayoutInfo
+import dev.chrisbanes.snapper.rememberSnapperFlingBehavior
 import kotlinx.coroutines.flow.collect
 import kotlinx.coroutines.flow.filter
 
@@ -59,34 +67,47 @@ annotation class ExperimentalPagerApi
  */
 @ExperimentalPagerApi
 object PagerDefaults {
+    /**
+     * The default implementation for the `maximumFlingDistance` parameter of
+     * [flingBehavior] which limits the fling distance to a single page.
+     */
+    @ExperimentalSnapperApi
+    @Suppress("MemberVisibilityCanBePrivate")
+    val singlePageFlingDistance: (SnapperLayoutInfo) -> Float = { layoutInfo ->
+        // We can scroll up to the scrollable size of the lazy layout
+        layoutInfo.endScrollOffset - layoutInfo.startScrollOffset.toFloat()
+    }
+
     /**
      * Remember the default [FlingBehavior] that represents the scroll curve.
      *
+     * Please remember to provide the correct [endContentPadding] if supplying your own
+     * [FlingBehavior] to [VerticalPager] or [HorizontalPager]. See those functions for how they
+     * calculate the value.
+     *
      * @param state The [PagerState] to update.
      * @param decayAnimationSpec The decay animation spec to use for decayed flings.
      * @param snapAnimationSpec The animation spec to use when snapping.
+     * @param maximumFlingDistance Block which returns the maximum fling distance in pixels.
+     * @param endContentPadding The amount of content padding on the end edge of the lazy list
+     * in pixels (end/bottom depending on the scrolling direction).
      */
     @Composable
+    @ExperimentalSnapperApi
     fun flingBehavior(
         state: PagerState,
         decayAnimationSpec: DecayAnimationSpec<Float> = rememberSplineBasedDecay(),
-        snapAnimationSpec: AnimationSpec<Float> = SnappingFlingBehaviorDefaults.snapAnimationSpec,
-    ): FlingBehavior = rememberSnappingFlingBehavior(
+        snapAnimationSpec: AnimationSpec<Float> = SnapperFlingBehaviorDefaults.SpringAnimationSpec,
+        maximumFlingDistance: (SnapperLayoutInfo) -> Float = singlePageFlingDistance,
+        endContentPadding: Dp = 0.dp,
+    ): FlingBehavior = rememberSnapperFlingBehavior(
         lazyListState = state.lazyListState,
+        snapOffsetForItem = SnapOffsets.Start, // pages are full width, so we use the simplest
         decayAnimationSpec = decayAnimationSpec,
-        snapAnimationSpec = snapAnimationSpec,
-    )
-
-    @Deprecated(
-        "Replaced with PagerDefaults.flingBehavior()",
-        ReplaceWith("PagerDefaults.flingBehavior(state, decayAnimationSpec, snapAnimationSpec)")
+        springAnimationSpec = snapAnimationSpec,
+        maximumFlingDistance = maximumFlingDistance,
+        endContentPadding = endContentPadding,
     )
-    @Composable
-    fun rememberPagerFlingConfig(
-        state: PagerState,
-        decayAnimationSpec: DecayAnimationSpec<Float> = rememberSplineBasedDecay(),
-        snapAnimationSpec: AnimationSpec<Float> = SnappingFlingBehaviorDefaults.snapAnimationSpec,
-    ): FlingBehavior = flingBehavior(state, decayAnimationSpec, snapAnimationSpec)
 }
 
 /**
@@ -108,6 +129,7 @@ object PagerDefaults {
  * @param content a block which describes the content. Inside this block you can reference
  * [PagerScope.currentPage] and other properties in [PagerScope].
  */
+@OptIn(ExperimentalSnapperApi::class)
 @ExperimentalPagerApi
 @Composable
 fun HorizontalPager(
@@ -116,10 +138,13 @@ fun HorizontalPager(
     state: PagerState = rememberPagerState(),
     reverseLayout: Boolean = false,
     itemSpacing: Dp = 0.dp,
-    flingBehavior: FlingBehavior = PagerDefaults.flingBehavior(state),
+    contentPadding: PaddingValues = PaddingValues(0.dp),
     verticalAlignment: Alignment.Vertical = Alignment.CenterVertically,
+    flingBehavior: FlingBehavior = PagerDefaults.flingBehavior(
+        state = state,
+        endContentPadding = contentPadding.calculateEndPadding(LayoutDirection.Ltr),
+    ),
     key: ((page: Int) -> Any)? = null,
-    contentPadding: PaddingValues = PaddingValues(0.dp),
     content: @Composable PagerScope.(page: Int) -> Unit,
 ) {
     Pager(
@@ -156,6 +181,7 @@ fun HorizontalPager(
  * @param content a block which describes the content. Inside this block you can reference
  * [PagerScope.currentPage] and other properties in [PagerScope].
  */
+@OptIn(ExperimentalSnapperApi::class)
 @ExperimentalPagerApi
 @Composable
 fun VerticalPager(
@@ -164,10 +190,13 @@ fun VerticalPager(
     state: PagerState = rememberPagerState(),
     reverseLayout: Boolean = false,
     itemSpacing: Dp = 0.dp,
-    flingBehavior: FlingBehavior = PagerDefaults.flingBehavior(state),
+    contentPadding: PaddingValues = PaddingValues(0.dp),
     horizontalAlignment: Alignment.Horizontal = Alignment.CenterHorizontally,
+    flingBehavior: FlingBehavior = PagerDefaults.flingBehavior(
+        state = state,
+        endContentPadding = contentPadding.calculateBottomPadding(),
+    ),
     key: ((page: Int) -> Any)? = null,
-    contentPadding: PaddingValues = PaddingValues(0.dp),
     content: @Composable PagerScope.(page: Int) -> Unit,
 ) {
     Pager(
@@ -206,7 +235,8 @@ internal fun Pager(
     // Provide our PagerState with access to the SnappingFlingBehavior animation target
     // TODO: can this be done in a better way?
     state.flingAnimationTarget = {
-        (flingBehavior as? SnappingFlingBehavior)?.animationTarget
+        @OptIn(ExperimentalSnapperApi::class)
+        (flingBehavior as? SnapperFlingBehavior)?.animationTarget
     }
 
     LaunchedEffect(count) {

pager/src/main/java/com/google/accompanist/pager/PagerState.kt

@@ -42,24 +42,6 @@ import io.github.aakira.napier.Napier
 import kotlin.math.absoluteValue
 import kotlin.math.roundToInt
 
-@Deprecated(
-    "Replaced with rememberPagerState(initialPage) and count parameter on Pager composables",
-    ReplaceWith("rememberPagerState(initialPage)"),
-    level = DeprecationLevel.ERROR,
-)
-@Suppress("UNUSED_PARAMETER", "NOTHING_TO_INLINE")
-@ExperimentalPagerApi
-@Composable
-inline fun rememberPagerState(
-    @IntRange(from = 0) pageCount: Int,
-    @IntRange(from = 0) initialPage: Int = 0,
-    @FloatRange(from = 0.0, to = 1.0) initialPageOffset: Float = 0f,
-    @IntRange(from = 1) initialOffscreenLimit: Int = 1,
-    infiniteLoop: Boolean = false
-): PagerState {
-    return rememberPagerState(initialPage = initialPage)
-}
-
 /**
  * Creates a [PagerState] that is remembered across compositions.
  *
@@ -97,9 +79,7 @@ class PagerState(
     private var _currentPage by mutableStateOf(currentPage)
 
     private val currentLayoutPageInfo: LazyListItemInfo?
-        get() = lazyListState.layoutInfo.visibleItemsInfo.asSequence()
-            .filter { it.offset <= 0 && it.offset + it.size > 0 }
-            .lastOrNull()
+        get() = lazyListState.layoutInfo.visibleItemsInfo.lastOrNull { it.offset <= 0 }
 
     private val currentLayoutPageOffset: Float
         get() = currentLayoutPageInfo?.let { current ->