Add Gmail-style vertical swipe-to-select for thread multi-selection

[Copilot]

This change adds drag-to-select behavior to the thread list while multi-selection mode is already active. Users can now vertically swipe across items to select or deselect multiple threads in one gesture, without interfering with horizontal swipe actions.

• New touch listener for drag selection

  • Added SwipeToSelectTouchListener (RecyclerView.OnItemTouchListener) in ui/main/folder.
  • Activates only when:
    • multi-select is enabled, and
    • gesture is clearly vertical (dy > touchSlop && dy > dx).
  • Captures gesture intent from the first touched thread:
    • first thread unselected → select all crossed threads
    • first thread selected → deselect all crossed threads
  • Applies intent per crossed item, publishes selection updates, sends SELECTED_STATE payload updates, and triggers haptic feedback when crossing item boundaries.
  • Resets listener state on UP, CANCEL, or disallow-intercept.

• Adapter API for position-to-thread lookup

  • Added ThreadListAdapter.getThreadAt(position: Int): Thread? to expose content-thread access safely from adapter positions.

• Fragment wiring

  • Registered SwipeToSelectTouchListener in ThreadListFragment.setupAdapter().
  • Bound it to MainViewModel multi-selection state via a MultiSelectionListener<Thread> adapter.

if (dy > touchSlop && dy > dx) {
    val startThread = (rv.adapter as? ThreadListAdapter)?.getThreadAt(startPosition)
    selectionIntent = startThread != null && !multiSelection.selectedItems.contains(startThread)
}

Original prompt

Goal

Add a "swipe-to-select" gesture to the email thread list so that, when multi-selection mode is already active, the user can drag their finger vertically across list items to select (or deselect) multiple threads in one motion — similar to Gmail on Android.

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Context

Relevant files (all in app/src/main/java/com/infomaniak/mail/ui/main/folder/):

• ThreadListAdapter.kt — extends DragDropSwipeAdapter. Multi-select is toggled via toggleMultiSelectedThread(). Exposes multiSelection: MultiSelectionListener<Thread> (private). dataSet comes from the parent DragDropSwipeAdapter.
• ThreadListFragment.kt — sets up the RecyclerView in setupAdapter(). Attaches the swipeListener (horizontal actions). Calls unlockSwipeActionsIfSet() which disables horizontal swipe directions when isMultiSelectOn == true.
• MultiSelectionListener.kt — interface with isEnabled, selectedItems: MutableSet<Thread>, publishSelectedItems: () -> Unit.
• ThreadListMultiSelection.kt — handles multi-select actions (archive, delete, etc.).
• ThreadListItem.kt — sealed class; ThreadListItem.Content(val thread: Thread) is the item type for emails.

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What to implement

1. New file: SwipeToSelectTouchListener.kt

Create app/src/main/java/com/infomaniak/mail/ui/main/folder/SwipeToSelectTouchListener.kt.

This class implements RecyclerView.OnItemTouchListener and provides Gmail-style drag-to-select behaviour:

• onInterceptTouchEvent:

  • On ACTION_DOWN: record the start coordinates and the item position under the finger. Do NOT intercept yet.
  • On ACTION_MOVE: if multiSelection.isEnabled is true AND the vertical displacement exceeds scaledTouchSlop AND the vertical displacement is greater than the horizontal displacement (so it's clearly a vertical drag, not a horizontal swipe), set isActive = true and return true to steal the event stream. When activating, record the selection state of the item at the start position (was it already selected?) — this determines the intent for the whole gesture: if the first item was unselected → the gesture selects all touched items; if it was selected → the gesture deselects all touched items.
  • Otherwise return isActive.

• onTouchEvent:

  • On ACTION_MOVE: use rv.findChildViewUnder(e.x, e.y) to find the item currently under the finger. If it is a new position (not the last one processed), and it is a ThreadListItem.Content, apply the intent (add or remove from selectedItems), call publishSelectedItems(), and call rv.adapter?.notifyItemChanged(pos, ThreadListAdapter.NotificationType.SELECTED_STATE). Also perform haptic feedback (HapticFeedbackConstants.VIRTUAL_KEY) when the finger crosses from one item to the next.
  • On ACTION_UP / ACTION_CANCEL: reset isActive, lastSelectedPosition, startY, startX, selectionIntent.

• onRequestDisallowInterceptTouchEvent: if disallowIntercept is true, reset isActive.

package com.infomaniak.mail.ui.main.folder

import android.view.HapticFeedbackConstants
import android.view.MotionEvent
import android.view.ViewConfiguration
import androidx.recyclerview.widget.RecyclerView
import com.infomaniak.mail.data.models.thread.Thread
import kotlin.math.abs

class SwipeToSelectTouchListener(
    recyclerView: RecyclerView,
    private val multiSelection: MultiSelectionListener<Thread>,
) : RecyclerView.OnItemTouchListener {

    private val touchSlop = ViewConfiguration.get(recyclerView.context).scaledTouchSlop
    private var isActive = false
    private var startX = 0f
    private var startY = 0f
    private var lastSelectedPosition = RecyclerView.NO_POSITION
    private var selectionIntent: Boolean? = null // true = select, false = deselect

    override fun onInterceptTouchEvent(rv: RecyclerView, e: MotionEvent): Boolean {
        when (e.actionMasked) {
            MotionEvent.ACTION_DOWN -> {
                startX = e.x
                startY = e.y
                lastSelectedPosition = RecyclerView.NO_POSITION
                selectionIntent = null
                isActive = false
            }
            MotionEvent.ACTION_MOVE -> {
                if (!isActive && multiSelection.isEnabled) {
                    val dy = abs(e.y - startY)
                    val dx = abs(e.x - startX)
                    if (dy > touchSlop && dy > dx) {
                        // Determine intent from the item at the start position
                        val startView = rv.findChildViewUnder(startX, startY)
                        if (startView != null) {
                            val startPos = rv.getChildAdapterPosition(startView)
                            if (startPos != RecyclerView.NO_POSITION) {
                                val startItem = (rv.adapter as? ThreadListAdapter)?.getThreadAt(startPos)
                                selectionIntent = startItem != null && !multiSelection.selectedItems.contai...

</details>



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[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
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0.0% Coverage on New Code
0.0% Duplication on New Code

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