/*
* Copyright 2022 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.compose.ui.input.nestedscroll
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.setValue
import androidx.compose.ui.geometry.Offset
import androidx.compose.ui.modifier.ModifierLocalConsumer
import androidx.compose.ui.modifier.ModifierLocalProvider
import androidx.compose.ui.modifier.ModifierLocalReadScope
import androidx.compose.ui.modifier.ProvidableModifierLocal
import androidx.compose.ui.modifier.modifierLocalOf
import androidx.compose.ui.unit.Velocity
import kotlinx.coroutines.CoroutineScope
internal val ModifierLocalNestedScroll = modifierLocalOf<NestedScrollModifierLocal?> { null }
/**
* NestedScroll using ModifierLocal as implementation.
*/
internal class NestedScrollModifierLocal(
val dispatcher: NestedScrollDispatcher,
val connection: NestedScrollConnection
) : ModifierLocalConsumer, ModifierLocalProvider<NestedScrollModifierLocal?>,
NestedScrollConnection {
init {
dispatcher.calculateNestedScrollScope = { nestedCoroutineScope }
}
private var parent: NestedScrollModifierLocal? by mutableStateOf(null)
private val nestedCoroutineScope: CoroutineScope
get() = parent?.nestedCoroutineScope
?: dispatcher.originNestedScrollScope
?: throw IllegalStateException(
"in order to access nested coroutine scope you need to attach dispatcher to the " +
"`Modifier.nestedScroll` first."
)
override val key: ProvidableModifierLocal<NestedScrollModifierLocal?>
get() = ModifierLocalNestedScroll
override val value: NestedScrollModifierLocal
get() = this
override fun onModifierLocalsUpdated(scope: ModifierLocalReadScope) = with(scope) {
parent = ModifierLocalNestedScroll.current
dispatcher.parent = parent
}
override fun onPreScroll(
available: Offset,
source: NestedScrollSource
): Offset {
val parentPreConsumed = parent?.onPreScroll(available, source) ?: Offset.Zero
val selfPreConsumed = connection.onPreScroll(available - parentPreConsumed, source)
return parentPreConsumed + selfPreConsumed
}
override fun onPostScroll(
consumed: Offset,
available: Offset,
source: NestedScrollSource
): Offset {
val selfConsumed = connection.onPostScroll(consumed, available, source)
val parentConsumed =
parent?.onPostScroll(consumed + selfConsumed, available - selfConsumed, source)
?: Offset.Zero
return selfConsumed + parentConsumed
}
override suspend fun onPreFling(available: Velocity): Velocity {
val parentPreConsumed = parent?.onPreFling(available) ?: Velocity.Zero
val selfPreConsumed = connection.onPreFling(available - parentPreConsumed)
return parentPreConsumed + selfPreConsumed
}
override suspend fun onPostFling(consumed: Velocity, available: Velocity): Velocity {
val selfConsumed = connection.onPostFling(consumed, available)
val parentConsumed =
parent?.onPostFling(consumed + selfConsumed, available - selfConsumed) ?: Velocity.Zero
return selfConsumed + parentConsumed
}
}