Support combine KeyItemMaps

library/src/main/java/me/gm/selection/KeyIndexItemMap.kt

@@ -25,12 +25,19 @@ import androidx.compose.runtime.remember
  * @see [androidx.compose.foundation.lazy.layout.LazyLayoutKeyIndexMap]
  */
 sealed interface KeyIndexItemMap<K, V> {
+    val items: List<V>
 
     fun getItem(e: K): V?
 
     fun getFullItemMappings(): Iterable<Pair<K, V>>
 }
 
+interface KeyItemMap<V> : KeyIndexItemMap<Any, V> {
+    val key: (index: Int) -> Any
+}
+
+interface IndexItemMap<V> : KeyIndexItemMap<Int, V>
+
 /**
  * Automatically deselect removed keys when items change.
  */
@@ -60,7 +67,7 @@ fun <V> rememberKeyItemMap(
     }
 
     return remember(items, key) {
-        KeyItemMap(items) { index -> key(items[index]) }
+        KeyItemMapImpl(items) { index -> key(items[index]) }
     }
 }
 
@@ -76,17 +83,17 @@ fun <V> rememberKeyItemMap(
     }
 
     return remember(items, key) {
-        KeyItemMap(items) { index -> key(index, items[index]) }
+        KeyItemMapImpl(items) { index -> key(index, items[index]) }
     }
 }
 
 /**
  * @see [androidx.compose.foundation.lazy.layout.NearestRangeKeyIndexMap]
  */
-open class KeyItemMap<V>(
-    val items: List<V>,
-    val key: ((index: Int) -> Any),
-) : KeyIndexItemMap<Any, V> {
+open class KeyItemMapImpl<V>(
+    override val items: List<V>,
+    override val key: (index: Int) -> Any,
+) : KeyItemMap<V> {
     private val map: MutableScatterMap<Any, V> = MutableScatterMap()
 
     override fun getItem(e: Any): V? = map.getOrElse(e) {
@@ -117,20 +124,55 @@ fun <V> rememberIndexItemMap(
     }
 
     return remember(items) {
-        IndexItemMap(items)
+        IndexItemMapImpl(items)
     }
 }
 
-open class IndexItemMap<V>(
-    val items: List<V>
-) : KeyIndexItemMap<Int, V> {
+open class IndexItemMapImpl<V>(
+    override val items: List<V>
+) : IndexItemMap<V> {
 
     override fun getItem(e: Int): V? = items[e]
 
     override fun getFullItemMappings(): Iterable<Pair<Int, V>> =
         items.mapIndexed { index, item -> index to item }
 }
 
-operator fun KeyIndexItemMap<*, *>.plus(other: KeyIndexItemMap<*, *>): KeyIndexItemMap<*, *> {
-    TODO()
+/**
+ * This can only be used as a parameter for modifiers.
+ */
+private class CombinedKeyItemMap<V>(
+    val maps: MutableList<KeyItemMap<V>>,
+    override val items: List<V> = emptyList(),
+    override val key: (Int) -> Any = { throw UnsupportedOperationException() }
+) : KeyItemMap<V> {
+
+    override fun getItem(e: Any): V? {
+        for (map in maps) {
+            val item = map.getItem(e)
+            if (item != null) {
+                return item
+            }
+        }
+        return null
+    }
+
+    override fun getFullItemMappings(): Iterable<Pair<Int, V>> =
+        throw UnsupportedOperationException()
+}
+
+operator fun <V> KeyItemMap<V>.plus(other: KeyItemMap<V>): KeyItemMap<V> {
+    return if (this is CombinedKeyItemMap) {
+        this.maps.add(other)
+        this
+    } else {
+        CombinedKeyItemMap(mutableListOf(this, other))
+    }
 }
+
+/*
+ * Combining [IndexItemMap] requires knowing the position of each interval, which is similar to
+ * [androidx.compose.foundation.lazy.layout.MutableIntervalList].
+ * This introduces some implicit restrictions on usage, which we do not favor, and therefore,
+ * we do not provide a built-in implementation.
+ */

library/src/main/java/me/gm/selection/SelectionState.kt

@@ -56,7 +56,6 @@ fun <V> rememberKeySelectionState(
  * [noOpSaver] or [viewModelSaver] to keep the implementation simple. Alternatively, you can use
  * [autoSaver] or a custom [Saver] to ensure data is not lost
  * @param initialSelection the initial value for [SelectionSupport.selection]
- * @see [androidx.compose.foundation.lazy.layout.MutableIntervalList]
  */
 @Composable
 fun <V> rememberIndexSelectionState(

sample/src/main/AndroidManifest.xml

@@ -20,6 +20,7 @@
 
     <application
         android:allowBackup="true"
+        android:enableOnBackInvokedCallback="true"
         android:fullBackupContent="true"
         android:label="ComposeSelectionTracker Sample"
         android:theme="@android:style/Theme.Material.Light.NoActionBar">

sample/src/main/java/me/gm/selection/sample/SampleScreen.kt

@@ -68,6 +68,7 @@ import me.gm.selection.grid.selectableItems
 import me.gm.selection.grid.tapInActionModeToToggleGesture
 import me.gm.selection.list.dragAfterLongPressToSelectGesture
 import me.gm.selection.list.selectableItems
+import me.gm.selection.plus
 import me.gm.selection.rememberKeyItemMap
 import me.gm.selection.rememberKeySelectionState
 
@@ -78,12 +79,12 @@ import me.gm.selection.rememberKeySelectionState
 @Composable
 fun SampleScreen() {
     val itemsA = remember {
-        List(10) { index ->
+        List(8) { index ->
             index
         }
     }
     val itemsB = remember {
-        List(10) { index ->
+        List(8) { index ->
             index
         }
     }
@@ -123,6 +124,11 @@ fun SampleScreen() {
             key = { item -> "A" to item },
             state = selectionState
         )
+        val mapB = rememberKeyItemMap(
+            items = itemsB,
+            key = { item -> "B" to item },
+            state = selectionState
+        )
         Column(
             modifier = Modifier
                 .fillMaxSize()
@@ -135,7 +141,9 @@ fun SampleScreen() {
                         modifier = Modifier
                             .fillMaxSize()
                             .weight(1f)
-                            .dragAfterLongPressToSelectGesture(listState, selectionState, mapA),
+                            .dragAfterLongPressToSelectGesture(
+                                listState, selectionState, mapA + mapB
+                            ),
                         state = listState
                     ) {
                         selectableItems(
@@ -155,6 +163,23 @@ fun SampleScreen() {
                                 text = "ItemA $item",
                             )
                         }
+                        selectableItems(
+                            state = selectionState,
+                            map = mapB
+                        ) { helper, item ->
+                            val context = LocalContext.current
+                            SampleListItem(
+                                modifier = Modifier
+                                    .animateItemPlacement()
+                                    .clickable {
+                                        Toast
+                                            .makeText(context, "ItemB $item", Toast.LENGTH_SHORT)
+                                            .show()
+                                    },
+                                helper = helper,
+                                text = "ItemB $item",
+                            )
+                        }
                     }
                 }