Drag Shadow Using Item Touch Helper android

Question

ItemTouchhelper Class in android helps only to move the entire view around the recyclerview. Is it possible to make a shadow of a view to be dragged(The original view to be in its place-fixed) using the Item touchHelper class?

Answer 1

I overrode onChildDraw and made my own shadow

public void onChildDraw(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
        super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);

        if (isCurrentlyActive) {
            if (actionState == ItemTouchHelper.ACTION_STATE_DRAG) {
                // make shadown
                isRotated = true;
            }
        } else {
            // view is going back to orig
            if (isRotated) {
                // undo shadow
            }
        }
    }

Answer 2

Here's a simple way to achieve shadow on the dragged item (for API >= 21 since it relies on elevation).

Declare an attribute in attrs.xml:

<attr name="draggedItemElevation" format="dimension"/>

Set the attribute value in your theme:

<style name="AppTheme" parent="...">
    <item name="draggedItemElevation">2dp</item>
</style>

Use this callback for the ItemTouchHelper:

class DragItemTouchHelperCallback : ItemTouchHelper.Callback() {

    // Get elevation in pixels from ?attr/draggedItemElevation.
    private val elevation = context.obtainStyledAttributes(
            intArrayOf(R.attr.editDraggedItemElevation)).use {
        it.getDimensionPixelSize(0, 0).toFloat()
    }

    override fun onChildDraw(c: Canvas, recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder,
                             dX: Float, dY: Float, actionState: Int, isCurrentlyActive: Boolean) {
        val view = viewHolder.itemView
        view.translationX = dX
        view.translationY = dY
        if (isCurrentlyActive) {
            ViewCompat.setElevation(view, elevation)
        }
    }

    override fun clearView(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder) {
        val view = viewHolder.itemView
        view.translationX = 0f
        view.translationY = 0f
        ViewCompat.setElevation(view, 0f)
    }

    override fun getMovementFlags(recyclerView: RecyclerView,
                                  viewHolder: RecyclerView.ViewHolder): Int {
        // ...
    }

    override fun onMove(recyclerView: RecyclerView,
                        viewHolder: RecyclerView.ViewHolder,
                        target: RecyclerView.ViewHolder): Boolean {
        // ...
    }

    override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {
        // ...
    }
}

This will temporarily change the dragged item elevation to ?attr/draggedItemElevation, then set it back to 0 when the item is dropped.