Move adapter manipulation logic to DpadDragHelper since it is error p…

…rone

dpadrecyclerview/src/main/java/com/rubensousa/dpadrecyclerview/DpadDragHelper.kt

@@ -19,8 +19,16 @@ package com.rubensousa.dpadrecyclerview
 import android.view.KeyEvent
 import android.view.View
 import androidx.recyclerview.widget.RecyclerView
+import java.util.Collections
 
-class DpadDragHelper(
+/**
+ * A helper class for re-ordering the contents of a [DpadRecyclerView].
+ *
+ * To use this, your adapter needs to implement [DpadDragHelper.DragAdapter]
+ * and expose the mutable collection via [DpadDragHelper.DragAdapter.getMutableItems].
+ */
+class DpadDragHelper<T>(
+    private val adapter: DragAdapter<T>,
     private val callback: DragCallback,
     private val cancelKeyCodes: Set<Int> = setOf(
         KeyEvent.KEYCODE_DPAD_CENTER,
@@ -48,6 +56,10 @@ class DpadDragHelper(
         }
     }
 
+    /**
+     * Attaches the [DpadRecyclerView] that will be dragged.
+     * This is required before calling [startDrag]
+     */
     fun attachRecyclerView(recyclerView: DpadRecyclerView) {
         if (currentRecyclerView === recyclerView) {
             return
@@ -56,11 +68,15 @@ class DpadDragHelper(
         currentRecyclerView = recyclerView
     }
 
+    /**
+     * Detaches the previously attached [DpadRecyclerView] and stops dragging
+     */
     fun detachFromRecyclerView() {
         stopDrag()
         currentRecyclerView = null
     }
 
+
     /**
      * Starts the dragging action for the ViewHolder at [position].
      *
@@ -125,24 +141,39 @@ class DpadDragHelper(
         }
         isDragging = false
         callback.onDragStopped()
-        currentRecyclerView?.requestLayout()
     }
 
     private fun onKeyEvent(event: KeyEvent): Boolean {
         val recyclerView = currentRecyclerView ?: return false
         val direction = getFocusDirection(event) ?: return false
         val view = recyclerView.focusSearch(direction) ?: return false
-        val viewHolder = recyclerView.findContainingViewHolder(view) ?: return false
+        val targetViewHolder = recyclerView.findContainingViewHolder(view) ?: return false
         val selectedViewHolder = recyclerView.findViewHolderForAdapterPosition(
             recyclerView.getSelectedPosition()
         ) ?: return false
 
         if (selectedViewHolder.absoluteAdapterPosition == RecyclerView.NO_POSITION
-            || viewHolder.absoluteAdapterPosition == RecyclerView.NO_POSITION
+            || targetViewHolder.absoluteAdapterPosition == RecyclerView.NO_POSITION
         ) {
             return false
         }
-        return callback.move(src = selectedViewHolder, target = viewHolder)
+        val currentAdapter = recyclerView.adapter ?: return false
+        if (recyclerView.getSpanCount() == 1) {
+            moveLinear(
+                adapter = currentAdapter,
+                items = adapter.getMutableItems(),
+                srcIndex = selectedViewHolder.bindingAdapterPosition,
+                targetIndex = targetViewHolder.bindingAdapterPosition
+            )
+        } else {
+            moveGrid(
+                adapter = currentAdapter,
+                items = adapter.getMutableItems(),
+                srcIndex = selectedViewHolder.bindingAdapterPosition,
+                targetIndex = targetViewHolder.bindingAdapterPosition
+            )
+        }
+        return true
     }
 
     private fun getFocusDirection(event: KeyEvent): Int? {
@@ -155,28 +186,64 @@ class DpadDragHelper(
         }
     }
 
-    interface DragCallback {
+    /**
+     * A linear move just swaps positions
+     */
+    private fun moveLinear(
+        adapter: RecyclerView.Adapter<*>,
+        items: MutableList<T>,
+        srcIndex: Int,
+        targetIndex: Int
+    ) {
+        Collections.swap(items, srcIndex, targetIndex)
+        adapter.notifyItemMoved(srcIndex, targetIndex)
+    }
+
+    /**
+     * A grid move needs to remove the element at the given position
+     * and insert it in the new position, otherwise order is not kept
+     */
+    private fun moveGrid(
+        adapter: RecyclerView.Adapter<*>,
+        items: MutableList<T>,
+        srcIndex: Int,
+        targetIndex: Int
+    ) {
+        val item = items.removeAt(srcIndex)
+        items.add(targetIndex, item)
+        adapter.notifyItemMoved(srcIndex, targetIndex)
+        /**
+         * Now notify the range that was affected
+         * If src < target -> notify all indexes from src until target
+         * If src > target -> notify all indexes from target until src
+         */
+        if (srcIndex < targetIndex) {
+            adapter.notifyItemRangeChanged(srcIndex, targetIndex - srcIndex)
+        } else {
+            adapter.notifyItemRangeChanged(targetIndex, srcIndex - targetIndex)
+        }
+    }
 
+    interface DragAdapter<T> {
         /**
-         * @return true if [src] should be moved to [target]'s position,
-         * false to keep the original positions
+         * @return the mutable collection of items backing the adapter
          */
-        fun move(
-            src: RecyclerView.ViewHolder,
-            target: RecyclerView.ViewHolder
-        ): Boolean
+        fun getMutableItems(): MutableList<T>
+    }
+
+    interface DragCallback {
 
         /**
          * Indicates that the dragging action has started. [DpadRecyclerView] will receive focus
          *
          * @param viewHolder the view holder that is being dragged
          */
-        fun onDragStarted(viewHolder: RecyclerView.ViewHolder) {}
+        fun onDragStarted(viewHolder: RecyclerView.ViewHolder)
 
         /**
          * Indicates that the dragging action has stopped
          */
-        fun onDragStopped() {}
+        fun onDragStopped()
     }
 
 }

sample/src/main/java/com/rubensousa/dpadrecyclerview/sample/ui/screen/drag/DragAdapter.kt

@@ -19,6 +19,7 @@ package com.rubensousa.dpadrecyclerview.sample.ui.screen.drag
 import android.view.ViewGroup
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import androidx.recyclerview.widget.RecyclerView
+import com.rubensousa.dpadrecyclerview.DpadDragHelper
 import com.rubensousa.dpadrecyclerview.compose.DpadComposeFocusViewHolder
 import com.rubensousa.dpadrecyclerview.sample.ui.model.ListTypes
 import com.rubensousa.dpadrecyclerview.sample.ui.widgets.common.MutableListAdapter
@@ -29,7 +30,10 @@ class DragAdapter(
     private val dragState: StateFlow<Int?>,
     private val onDragStart: (viewHolder: RecyclerView.ViewHolder) -> Unit,
     private val gridLayout: Boolean = false
-) : MutableListAdapter<Int, DpadComposeFocusViewHolder<Int>>(MutableGridAdapter.DIFF_CALLBACK) {
+) : MutableListAdapter<Int, DpadComposeFocusViewHolder<Int>>(MutableGridAdapter.DIFF_CALLBACK),
+    DpadDragHelper.DragAdapter<Int> {
+
+    override fun getMutableItems(): MutableList<Int> = items
 
     override fun onCreateViewHolder(
         parent: ViewGroup,
@@ -64,8 +68,22 @@ class DragAdapter(
         holder.itemView.contentDescription = item.toString()
     }
 
+
     override fun getItemViewType(position: Int): Int {
         return ListTypes.ITEM
     }
 
+    override fun toString(): String {
+        val builder = StringBuilder()
+        builder.append("[")
+        for (i in 0 until itemCount) {
+            builder.append(getItem(i))
+            if (i < itemCount - 1) {
+                builder.append(", ")
+            }
+        }
+        builder.append("]")
+        return builder.toString()
+    }
+
 }

sample/src/main/java/com/rubensousa/dpadrecyclerview/sample/ui/screen/drag/DragAndDropFragment.kt

@@ -44,28 +44,17 @@ class DragAndDropFragment : Fragment(R.layout.screen_drag_drop) {
             startDrag(viewHolder)
         }
     )
-    private val dragHelper = DpadDragHelper(object : DpadDragHelper.DragCallback {
-
-        override fun move(
-            src: RecyclerView.ViewHolder,
-            target: RecyclerView.ViewHolder
-        ): Boolean {
-            dragAdapter.move(
-                from = src.bindingAdapterPosition,
-                to = target.bindingAdapterPosition
-            )
-            return true
-        }
-
-        override fun onDragStarted(viewHolder: RecyclerView.ViewHolder) {
-            dragState.value = dragAdapter.getItem(viewHolder.bindingAdapterPosition)
-        }
-
-        override fun onDragStopped() {
-            dragState.value = null
+    private val dragHelper = DpadDragHelper(
+        adapter = dragAdapter,
+        callback = object : DpadDragHelper.DragCallback {
+            override fun onDragStarted(viewHolder: RecyclerView.ViewHolder) {
+                dragState.value = dragAdapter.getItem(viewHolder.bindingAdapterPosition)
+            }
+            override fun onDragStopped() {
+                dragState.value = null
+            }
         }
-
-    })
+    )
 
     override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
         super.onViewCreated(view, savedInstanceState)

sample/src/main/java/com/rubensousa/dpadrecyclerview/sample/ui/screen/drag/DragAndDropGridFragment.kt

@@ -45,34 +45,23 @@ class DragAndDropGridFragment : Fragment(R.layout.screen_drag_drop_grid) {
         },
         gridLayout = true
     )
-    private val dragHelper = DpadDragHelper(object : DpadDragHelper.DragCallback {
-
-        override fun move(
-            src: RecyclerView.ViewHolder,
-            target: RecyclerView.ViewHolder
-        ): Boolean {
-            dragAdapter.move(
-                from = src.absoluteAdapterPosition,
-                to = target.absoluteAdapterPosition
-            )
-            return true
-        }
-
-        override fun onDragStarted(viewHolder: RecyclerView.ViewHolder) {
-            dragState.value = dragAdapter.getItem(viewHolder.absoluteAdapterPosition)
-        }
-
-        override fun onDragStopped() {
-            dragState.value = null
+    private val dragHelper = DpadDragHelper(
+        adapter = dragAdapter,
+        callback = object : DpadDragHelper.DragCallback {
+            override fun onDragStarted(viewHolder: RecyclerView.ViewHolder) {
+                dragState.value = dragAdapter.getItem(viewHolder.bindingAdapterPosition)
+            }
+            override fun onDragStopped() {
+                dragState.value = null
+            }
         }
-
-    })
+    )
 
     override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
         super.onViewCreated(view, savedInstanceState)
         setupRecyclerView()
         setDragButtonContent()
-        dragAdapter.submitList(List(20) { it }.toMutableList())
+        dragAdapter.submitList(List(15) { it }.toMutableList())
     }
 
     private fun setupRecyclerView() {

sample/src/main/java/com/rubensousa/dpadrecyclerview/sample/ui/widgets/common/MutableListAdapter.kt

@@ -34,7 +34,7 @@ abstract class MutableListAdapter<T, VH : RecyclerView.ViewHolder>(
         private val MAIN_THREAD_HANDLER = Handler(Looper.getMainLooper())
     }
 
-    private var items: MutableList<T> = Collections.emptyList()
+    protected var items: MutableList<T> = Collections.emptyList()
     private var currentVersion = 0
 
     @SuppressLint("NotifyDataSetChanged")
@@ -128,12 +128,6 @@ abstract class MutableListAdapter<T, VH : RecyclerView.ViewHolder>(
 
     }
 
-    fun move(from: Int, to: Int) {
-        currentVersion++
-        Collections.swap(items, from, to)
-        notifyItemMoved(from, to)
-    }
-
     fun addAt(index: Int, item: T) {
         currentVersion++
         items.add(index, item)