PhotoGrid-Final.kt

/*
* Copyright 2023 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
*
*   https://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 com.example.myapplication

import androidx.compose.animation.core.animateDp
import androidx.compose.animation.core.updateTransition
import androidx.compose.foundation.Image
import androidx.compose.foundation.background
import androidx.compose.foundation.border
import androidx.compose.foundation.gestures.detectDragGesturesAfterLongPress
import androidx.compose.foundation.gestures.scrollBy
import androidx.compose.foundation.interaction.MutableInteractionSource
import androidx.compose.foundation.layout.Arrangement
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.aspectRatio
import androidx.compose.foundation.layout.padding
import androidx.compose.foundation.lazy.grid.GridCells
import androidx.compose.foundation.lazy.grid.LazyGridState
import androidx.compose.foundation.lazy.grid.LazyVerticalGrid
import androidx.compose.foundation.lazy.grid.items
import androidx.compose.foundation.lazy.grid.rememberLazyGridState
import androidx.compose.foundation.selection.toggleable
import androidx.compose.foundation.shape.CircleShape
import androidx.compose.foundation.shape.RoundedCornerShape
import androidx.compose.material.icons.Icons
import androidx.compose.material.icons.filled.CheckCircle
import androidx.compose.material.icons.filled.RadioButtonUnchecked
import androidx.compose.material3.Icon
import androidx.compose.material3.MaterialTheme
import androidx.compose.material3.Surface
import androidx.compose.material3.surfaceColorAtElevation
import androidx.compose.runtime.Composable
import androidx.compose.runtime.LaunchedEffect
import androidx.compose.runtime.MutableState
import androidx.compose.runtime.derivedStateOf
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.saveable.rememberSaveable
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.clip
import androidx.compose.ui.geometry.Offset
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.hapticfeedback.HapticFeedback
import androidx.compose.ui.hapticfeedback.HapticFeedbackType
import androidx.compose.ui.input.pointer.pointerInput
import androidx.compose.ui.platform.LocalDensity
import androidx.compose.ui.platform.LocalHapticFeedback
import androidx.compose.ui.semantics.onLongClick
import androidx.compose.ui.semantics.semantics
import androidx.compose.ui.tooling.preview.Preview
import androidx.compose.ui.unit.dp
import coil.compose.rememberAsyncImagePainter
import com.example.myapplication.ui.theme.MyApplicationTheme
import kotlinx.coroutines.delay

private class Photo(
  val id: Int,
  val url: String = "https://picsum.photos/seed/${(0..100000).random()}/256/256"
)

@Composable
private fun PhotosGrid(
  photos: List<Photo> = List(100) { Photo(it) },
  selectedIds: MutableState<Set<Int>> = rememberSaveable { mutableStateOf(emptySet()) }
) {
  val inSelectionMode by remember { derivedStateOf { selectedIds.value.isNotEmpty() } }
  val state = rememberLazyGridState()
  val autoScrollSpeed = remember { mutableStateOf(0f) }
  LaunchedEffect(autoScrollSpeed.value) {
    if (autoScrollSpeed.value != 0f) {
      while (isActive) {
        state.scrollBy(autoScrollSpeed.value)
        delay(10)
      }
    }
  }

  LazyVerticalGrid(
    state = state,
    columns = GridCells.Adaptive(minSize = 128.dp),
    verticalArrangement = Arrangement.spacedBy(3.dp),
    horizontalArrangement = Arrangement.spacedBy(3.dp),
    modifier = Modifier.photoGridDragHandler(
      lazyGridState = state,
      haptics = LocalHapticFeedback.current,
      selectedIds = selectedIds,
      autoScrollSpeed = autoScrollSpeed,
      autoScrollThreshold = with(LocalDensity.current) { 40.dp.toPx() }
    )
  ) {
    items(photos, key = { it.id }) { photo ->
      val selected by remember { derivedStateOf { selectedIds.value.contains(photo.id) } }
      ImageItem(
        photo, inSelectionMode, selected,
        Modifier
          .semantics {
            if (!inSelectionMode) {
              onLongClick("Select") {
                selectedIds.value += photo.id
                true
              }
            }
          }
          .then(if (inSelectionMode) {
            Modifier.toggleable(
              value = selected,
              interactionSource = remember { MutableInteractionSource() },
              indication = null, // do not show a ripple
              onValueChange = {
                if (it) {
                  selectedIds.value += photo.id
                } else {
                  selectedIds.value -= photo.id
                }
              }
            )
          } else Modifier)
      )
    }
  }
}

fun Modifier.photoGridDragHandler(
  lazyGridState: LazyGridState,
  haptics: HapticFeedback,
  selectedIds: MutableState<Set<Int>>,
  autoScrollSpeed: MutableState<Float>,
  autoScrollThreshold: Float
) = pointerInput(Unit) {
  fun LazyGridState.gridItemKeyAtPosition(hitPoint: Offset): Int? =
    layoutInfo.visibleItemsInfo.find { itemInfo ->
      itemInfo.size.toIntRect().contains(hitPoint.round() - itemInfo.offset)
    }?.key as? Int

  var initialKey: Int? = null
  var currentKey: Int? = null
  detectDragGesturesAfterLongPress(
    onDragStart = { offset ->
      lazyGridState.gridItemKeyAtPosition(offset)?.let { key ->
        if (!selectedIds.value.contains(key)) {
          haptics.performHapticFeedback(HapticFeedbackType.LongPress)
          initialKey = key
          currentKey = key
          selectedIds.value += key
        }
      }
    },
    onDragCancel = { initialKey = null; autoScrollSpeed.value = 0f },
    onDragEnd = { initialKey = null; autoScrollSpeed.value = 0f },
    onDrag = { change, _ ->
      if (initialKey != null) {
        val distFromBottom =
          lazyGridState.layoutInfo.viewportSize.height - change.position.y
        val distFromTop = change.position.y
        autoScrollSpeed.value = when {
          distFromBottom < autoScrollThreshold -> autoScrollThreshold - distFromBottom
          distFromTop < autoScrollThreshold -> -(autoScrollThreshold - distFromTop)
          else -> 0f
        }

        lazyGridState.gridItemKeyAtPosition(change.position)?.let { key ->
          if (currentKey != key) {
            selectedIds.value = selectedIds.value
              .minus(initialKey!!..currentKey!!)
              .minus(currentKey!!..initialKey!!)
              .plus(initialKey!!..key)
              .plus(key..initialKey!!)
            currentKey = key
          }
        }
      }
    }
  )
}

@Composable
private fun ImageItem(
  photo: Photo,
  inSelectionMode: Boolean,
  selected: Boolean,
  modifier: Modifier = Modifier
) {
  Surface(
    modifier = modifier.aspectRatio(1f),
    tonalElevation = 3.dp
  ) {
    Box {
      val transition = updateTransition(selected, label = "selected")
      val padding by transition.animateDp(label = "padding") { selected ->
        if (selected) 10.dp else 0.dp
      }
      val roundedCornerShape by transition.animateDp(label = "corner") { selected ->
        if (selected) 16.dp else 0.dp
      }
      Image(
        painter = rememberAsyncImagePainter(photo.url),
        contentDescription = null,
        modifier = Modifier
          .matchParentSize()
          .padding(padding)
          .clip(RoundedCornerShape(roundedCornerShape))
      )
      if (inSelectionMode) {
        if (selected) {
          val bgColor = MaterialTheme.colorScheme.surfaceColorAtElevation(3.dp)
          Icon(
            Icons.Filled.CheckCircle,
            tint = MaterialTheme.colorScheme.primary,
            contentDescription = null,
            modifier = Modifier
              .padding(4.dp)
              .border(2.dp, bgColor, CircleShape)
              .clip(CircleShape)
              .background(bgColor)
          )
        } else {
          Icon(
            Icons.Filled.RadioButtonUnchecked,
            tint = Color.White.copy(alpha = 0.7f),
            contentDescription = null,
            modifier = Modifier.padding(6.dp)
          )
        }
      }
    }
  }
}

@Preview
@Composable
private fun MyApp() {
  MyApplicationTheme { PhotosGrid() }
}

If anyone is interested, I've turned this gist into a Compose Multiplatform library