compose/foundation/foundation/samples/src/main/java/androidx/compose/foundation/samples/ScrollableSamples.kt

/*
 * Copyright 2020 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.foundation.samples

import androidx.annotation.Sampled
import androidx.compose.animation.core.AnimationSpec
import androidx.compose.animation.core.LinearEasing
import androidx.compose.animation.core.tween
import androidx.compose.foundation.ExperimentalFoundationApi
import androidx.compose.foundation.background
import androidx.compose.foundation.border
import androidx.compose.foundation.focusable
import androidx.compose.foundation.gestures.BringIntoViewSpec
import androidx.compose.foundation.gestures.LocalBringIntoViewSpec
import androidx.compose.foundation.gestures.Orientation
import androidx.compose.foundation.gestures.rememberScrollableState
import androidx.compose.foundation.gestures.scrollable
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.layout.padding
import androidx.compose.foundation.layout.size
import androidx.compose.foundation.layout.wrapContentHeight
import androidx.compose.foundation.lazy.LazyColumn
import androidx.compose.foundation.lazy.LazyRow
import androidx.compose.foundation.lazy.items
import androidx.compose.foundation.lazy.rememberLazyListState
import androidx.compose.material.Icon
import androidx.compose.material.Text
import androidx.compose.material.icons.Icons
import androidx.compose.material.icons.filled.KeyboardArrowDown
import androidx.compose.material.icons.filled.KeyboardArrowUp
import androidx.compose.runtime.Composable
import androidx.compose.runtime.CompositionLocalProvider
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.setValue
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.focus.onFocusChanged
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.graphics.graphicsLayer
import androidx.compose.ui.text.TextStyle
import androidx.compose.ui.unit.dp
import androidx.compose.ui.unit.sp
import kotlin.math.abs
import kotlin.math.roundToInt

@Sampled
@Composable
fun ScrollableSample() {
    // actual composable state that we will show on UI and update in `Scrollable`
    val offset = remember { mutableStateOf(0f) }
    Box(
        Modifier
            .size(150.dp)
            .scrollable(
                orientation = Orientation.Vertical,
                // state for Scrollable, describes how consume scroll amount
                state = rememberScrollableState { delta ->
                    // use the scroll data and indicate how much this element consumed.
                    // unconsumed deltas will be propagated to nested scrollables (if present)
                    offset.value = offset.value + delta // update the state
                    delta // indicate that we consumed all the pixels available
                }
            )
            .background(Color.LightGray),
        contentAlignment = Alignment.Center
    ) {
        // Modifier.scrollable is not opinionated about its children's layouts. It will however
        // promote nested scrolling capabilities if those children also use the modifier.
        // The modifier will not change any layouts so one must handle any desired changes through
        // the delta values in the scrollable state
        Text(offset.value.roundToInt().toString(), style = TextStyle(fontSize = 32.sp))
    }
}

@Sampled
@Composable
fun CanScrollSample() {
    val state = rememberLazyListState()
    Column(Modifier.fillMaxWidth(), horizontalAlignment = Alignment.CenterHorizontally) {
        Icon(
            Icons.Filled.KeyboardArrowUp,
            null,
            Modifier.graphicsLayer {
                // Hide the icon if we cannot scroll backward (we are the start of the list)
                // We use graphicsLayer here to control the alpha so that we only redraw when this
                // value changes, instead of recomposing
                alpha = if (state.canScrollBackward) 1f else 0f
            },
            Color.Red
        )
        val items = (1..100).toList()
        LazyColumn(
            Modifier
                .weight(1f)
                .fillMaxWidth(), state
        ) {
            items(items) {
                Text("Item is $it")
            }
        }
        Icon(
            Icons.Filled.KeyboardArrowDown,
            null,
            Modifier.graphicsLayer {
                // Hide the icon if we cannot scroll forward (we are the end of the list)
                // We use graphicsLayer here to control the alpha so that we only redraw when this
                // value changes, instead of recomposing
                alpha = if (state.canScrollForward) 1f else 0f
            },
            Color.Red
        )
    }
}

@ExperimentalFoundationApi
@Sampled
@Composable
fun FocusScrollingInLazyRowSample() {
    // a bring into view spec that pivots around the center of the scrollable container
    val customBringIntoViewSpec = object : BringIntoViewSpec {
        val customAnimationSpec = tween<Float>(easing = LinearEasing)
        override val scrollAnimationSpec: AnimationSpec<Float>
            get() = customAnimationSpec

        override fun calculateScrollDistance(
            offset: Float,
            size: Float,
            containerSize: Float
        ): Float {
            val trailingEdgeOfItemRequestingFocus = offset + size

            val sizeOfItemRequestingFocus =
                abs(trailingEdgeOfItemRequestingFocus - offset)
            val childSmallerThanParent = sizeOfItemRequestingFocus <= containerSize
            val initialTargetForLeadingEdge =
                containerSize / 2f - (sizeOfItemRequestingFocus / 2f)
            val spaceAvailableToShowItem = containerSize - initialTargetForLeadingEdge

            val targetForLeadingEdge =
                if (childSmallerThanParent &&
                    spaceAvailableToShowItem < sizeOfItemRequestingFocus
                ) {
                    containerSize - sizeOfItemRequestingFocus
                } else {
                    initialTargetForLeadingEdge
                }

            return offset - targetForLeadingEdge
        }
    }

    // LocalBringIntoViewSpec will apply to all scrollables in the hierarchy.
    CompositionLocalProvider(LocalBringIntoViewSpec provides customBringIntoViewSpec) {
        LazyRow(
            modifier = Modifier
                .fillMaxWidth()
                .wrapContentHeight()
        ) {
            items(100) {
                var color by remember { mutableStateOf(Color.White) }
                Box(
                    modifier = Modifier
                        .size(100.dp)
                        .padding(4.dp)
                        .background(Color.Gray)
                        .onFocusChanged {
                            color = if (it.isFocused) Color.Red else Color.White
                        }
                        .border(5.dp, color)
                        .focusable(),
                    contentAlignment = Alignment.Center
                ) {
                    Text(text = it.toString())
                }
            }
        }
    }
}