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Commit 08a4f97f authored by omarmt's avatar omarmt
Browse files

PriorityNestedScrollConnection simplification: remove onPostFling method 

To simplify the logic for acquiring priority during postFling, we've
added a canStartPostFling method. If this method returns true, it will
call onStart and then immediately onStop (since the last event was
launched during a nested scroll gesture).

Test: atest PriorityNestedScrollConnectionTest
Bug: 291025415
Change-Id: I7ade358f2097a15d1328f3e6706df0ec12d23acf
parent b51f7231

packages/SystemUI/compose/scene/src/com/android/compose/animation/scene/SwipeToScene.kt

+18 −20
Original line number Diff line number Diff line
@@ -556,6 +556,15 @@ class SceneNestedScrollHandler( 
        // moving on to the next scene.

        var gestureStartedOnNestedChild = false



        fun findNextScene(amount: Float): SceneKey? {

            val fromScene = gestureHandler.currentScene

            return when {

                amount < 0f -> fromScene.upOrLeft(gestureHandler.orientation)

                amount > 0f -> fromScene.downOrRight(gestureHandler.orientation)

                else -> null

            }

        }



        return PriorityNestedScrollConnection(

            canStartPreScroll = { offsetAvailable, offsetBeforeStart ->

                gestureStartedOnNestedChild = offsetBeforeStart != Offset.Zero
@@ -576,15 +585,16 @@ class SceneNestedScrollHandler( 
                if (amount == 0f) return@PriorityNestedScrollConnection false



                gestureStartedOnNestedChild = offsetBeforeStart != Offset.Zero

                nextScene = findNextScene(amount)

                nextScene != null

            },

            canStartPostFling = { velocityAvailable ->

                val amount = velocityAvailable.toAmount()

                if (amount == 0f) return@PriorityNestedScrollConnection false



                val fromScene = gestureHandler.currentScene

                nextScene =

                    when {

                        amount < 0f -> fromScene.upOrLeft(gestureHandler.orientation)

                        amount > 0f -> fromScene.downOrRight(gestureHandler.orientation)

                        else -> null

                    }



                // We could start an overscroll animation

                gestureStartedOnNestedChild = true

                nextScene = findNextScene(amount)

                nextScene != null

            },

            canContinueScroll = { priorityScene == gestureHandler.swipeTransitionToScene.key },
@@ -612,18 +622,6 @@ class SceneNestedScrollHandler( 
                // The onDragStopped animation consumes any remaining velocity.

                velocityAvailable

            },

            onPostFling = { velocityAvailable ->

                val velocityAmount = velocityAvailable.toAmount()

                if (velocityAmount != 0f) {

                    // If there is any velocity left, we can try running an overscroll animation

                    // between scenes.

                    gestureHandler.onDragStarted()

                    gestureHandler.onDragStopped(velocity = velocityAmount, canChangeScene = false)

                }



                // We consumed any remaining velocity.

                velocityAvailable

            },

        )

    }

}

packages/SystemUI/compose/scene/src/com/android/compose/nestedscroll/PriorityNestedScrollConnection.kt

+9 −2
Original line number Diff line number Diff line
@@ -34,11 +34,11 @@ import androidx.compose.ui.unit.Velocity 
class PriorityNestedScrollConnection(

    private val canStartPreScroll: (offsetAvailable: Offset, offsetBeforeStart: Offset) -> Boolean,

    private val canStartPostScroll: (offsetAvailable: Offset, offsetBeforeStart: Offset) -> Boolean,

    private val canStartPostFling: (velocityAvailable: Velocity) -> Boolean,

    private val canContinueScroll: () -> Boolean,

    private val onStart: () -> Unit,

    private val onScroll: (offsetAvailable: Offset) -> Offset,

    private val onStop: (velocityAvailable: Velocity) -> Velocity,

    private val onPostFling: suspend (velocityAvailable: Velocity) -> Velocity,

) : NestedScrollConnection {



    /** In priority mode [onPreScroll] events are first consumed by the parent, via [onScroll]. */
@@ -102,7 +102,14 @@ class PriorityNestedScrollConnection( 
    }



    override suspend fun onPostFling(consumed: Velocity, available: Velocity): Velocity {

        return onPostFling(available)

        if (!canStartPostFling(available)) {

            return Velocity.Zero

        }



        onPriorityStart(available = Offset.Zero)



        // This is the last event of a scroll gesture.

        return onPriorityStop(available)

    }



    /** Method to call before destroying the object or to reset the initial state. */

packages/SystemUI/compose/scene/tests/src/com/android/compose/nestedscroll/PriorityNestedScrollConnectionTest.kt

+26 −7
Original line number Diff line number Diff line
@@ -32,19 +32,19 @@ import org.junit.runner.RunWith 
class PriorityNestedScrollConnectionTest {

    private var canStartPreScroll = false

    private var canStartPostScroll = false

    private var canStartPostFling = false

    private var canContinueScroll = false

    private var isStarted = false

    private var lastScroll: Offset? = null

    private var returnOnScroll = Offset.Zero

    private var lastStop: Velocity? = null

    private var returnOnStop = Velocity.Zero

    private var lastOnPostFling: Velocity? = null

    private var returnOnPostFling = Velocity.Zero



    private val scrollConnection =

        PriorityNestedScrollConnection(

            canStartPreScroll = { _, _ -> canStartPreScroll },

            canStartPostScroll = { _, _ -> canStartPostScroll },

            canStartPostFling = { canStartPostFling },

            canContinueScroll = { canContinueScroll },

            onStart = { isStarted = true },

            onScroll = {
@@ -55,10 +55,6 @@ class PriorityNestedScrollConnectionTest { 
                lastStop = it

                returnOnStop

            },

            onPostFling = {

                lastOnPostFling = it

                returnOnPostFling

            },

        )



    private val offset1 = Offset(1f, 1f)
@@ -185,11 +181,34 @@ class PriorityNestedScrollConnectionTest { 


    @Test

    fun receive_onPostFling() = runTest {

        canStartPostFling = true



        scrollConnection.onPostFling(

            consumed = velocity1,

            available = velocity2,

        )



        assertThat(lastOnPostFling).isEqualTo(velocity2)

        assertThat(lastStop).isEqualTo(velocity2)

    }



    @Test

    fun step1_priorityModeShouldStartOnlyOnPostFling() = runTest {

        canStartPostFling = true



        scrollConnection.onPreScroll(available = Offset.Zero, source = NestedScrollSource.Drag)

        assertThat(isStarted).isEqualTo(false)



        scrollConnection.onPostScroll(

            consumed = Offset.Zero,

            available = Offset.Zero,

            source = NestedScrollSource.Drag

        )

        assertThat(isStarted).isEqualTo(false)



        scrollConnection.onPreFling(available = Velocity.Zero)

        assertThat(isStarted).isEqualTo(false)



        scrollConnection.onPostFling(consumed = Velocity.Zero, available = Velocity.Zero)

        assertThat(isStarted).isEqualTo(true)

    }

}