Android开发：如何在RecyclerView与Relative Layout间实现视图拖拽移动？

Hey there! I’ve built similar drag-and-drop features for puzzle apps before, so let’s walk through exactly how to get your puzzle pieces moving between RecyclerView and RelativeLayout. Here’s a step-by-step breakdown with code snippets to make it work:

First, you need to trigger the drag action when the user long-presses (or taps) a puzzle piece in your RecyclerView. Add this logic directly in your RecyclerView adapter’s ViewHolder:

class PuzzlePieceViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {
    init {
        // Use long press to start drag (you can switch to onClick if preferred)
        itemView.setOnLongClickListener { v ->
            // Create empty ClipData (we just need it for the drag framework)
            val clipData = ClipData.newPlainText("", "")
            val shadowBuilder = View.DragShadowBuilder(v)
            
            // Launch the drag operation
            v.startDragAndDrop(clipData, shadowBuilder, v, 0)
            // Optional: Dim the original view while dragging for better feedback
            v.alpha = 0.5f
            true
        }

        // Reset the view's appearance when drag finishes
        itemView.setOnDragListener { v, event ->
            if (event.action == DragEvent.ACTION_DRAG_ENDED) {
                v.alpha = 1.0f
            }
            true
        }
    }
}

Next, set up an OnDragListener on your RelativeLayout to accept dragged puzzle pieces. This listener will manage all drag-related events:

// In your Activity/Fragment
val puzzleDraftArea: RelativeLayout = findViewById(R.id.puzzle_draft_area)

puzzleDraftArea.setOnDragListener { v, event ->
    when (event.action) {
        DragEvent.ACTION_DRAG_STARTED -> {
            // Accept the drag (we're checking for plain text mime type, which matches our ClipData)
            event.clipDescription.hasMimeType(ClipDescription.MIMETYPE_TEXT_PLAIN)
        }
        DragEvent.ACTION_DRAG_ENTERED -> {
            // Optional: Highlight the draft area to signal it's a valid drop target
            v.setBackgroundColor(ContextCompat.getColor(v.context, R.color.drop_target_highlight))
            true
        }
        DragEvent.ACTION_DRAG_EXITED -> {
            // Remove highlight when the piece leaves the area
            v.setBackgroundColor(ContextCompat.getColor(v.context, R.color.transparent))
            true
        }
        DragEvent.ACTION_DROP -> {
            // Retrieve the dragged puzzle piece view
            val draggedView = event.localState as View
            val recyclerViewParent = draggedView.parent as RecyclerView

            // Remove the view from RecyclerView
            recyclerViewParent.removeView(draggedView)
            
            // Position the piece in the RelativeLayout based on drop coordinates
            val layoutParams = RelativeLayout.LayoutParams(
                ViewGroup.LayoutParams.WRAP_CONTENT,
                ViewGroup.LayoutParams.WRAP_CONTENT
            )
            // Center the piece on the drop point
            layoutParams.leftMargin = (event.x - draggedView.width/2).toInt()
            layoutParams.topMargin = (event.y - draggedView.height/2).toInt()
            
            draggedView.layoutParams = layoutParams
            puzzleDraftArea.addView(draggedView)

            // Reset the view's appearance
            draggedView.alpha = 1.0f
            // Update RecyclerView's data source and notify the adapter
            val adapter = recyclerViewParent.adapter as PuzzlePieceAdapter
            adapter.removeItem(adapter.getPosition(draggedView)) // Implement these methods in your adapter

            // Clear the highlight
            v.setBackgroundColor(ContextCompat.getColor(v.context, R.color.transparent))
            true
        }
        DragEvent.ACTION_DRAG_ENDED -> {
            // Clean up any leftover state
            v.setBackgroundColor(ContextCompat.getColor(v.context, R.color.transparent))
            true
        }
        else -> false
    }
}

Make sure your adapter has methods to track positions and remove items:

class PuzzlePieceAdapter(private val pieces: MutableList<PuzzlePiece>) : RecyclerView.Adapter<PuzzlePieceViewHolder>() {
    // ... Implement onCreateViewHolder, onBindViewHolder, getItemCount as usual ...

    fun removeItem(position: Int) {
        pieces.removeAt(position)
        notifyItemRemoved(position)
    }

    fun getPosition(view: View): Int {
        // Use the tag we set in onBindViewHolder to find the item's position
        return view.tag as Int
    }

    override fun onBindViewHolder(holder: PuzzlePieceViewHolder, position: Int) {
        // Bind your puzzle piece data here
        holder.itemView.tag = position // Store position as a tag for easy lookup
    }
}

• View Reusability: RecyclerView recycles views, so always reset drag-related state (like alpha) in the ACTION_DRAG_ENDED listener to avoid weird visual bugs.
• Position Tracking: Using view.tag to store the adapter position is a simple, reliable way to find which item to remove when dropping.
• Custom Drag Shadow: If you want the dragged piece to match the original perfectly, you can extend View.DragShadowBuilder to customize the shadow appearance.

That should get your puzzle pieces dragging and dropping smoothly between the two areas! Let me know if you hit any specific snags with your implementation.

内容的提问来源于stack exchange，提问作者H. Kardesler