Who Won the Drag

Same finger. Same vertical drag. Two Harbor cards inside one ScrollView.

Which one moves?

Idle — both at zero

PRIORITY will use .highPriorityGesture with a sequenced long-press → drag. PLAIN is the control: the same DragGesture via plain .gesture.

Armed — long-press first

LongPressGesture(minimumDuration: 0.35)
  .sequenced(before: DragGesture(minimumDistance: 4))

Observed: PHASE ARMED, tape LONGPRESS, PRIORITY detail armed, offset still 0 pt. Sequencing matters — the drag has not started yet.

Priority wins — 72 pt

Tape: LONGPRESS · DRAG+72. Footer: P 72 · L 0.

.highPriorityGesture tells the scroll view to yield. The card moves; the list does not.

Plain loses — scroll won

PHASE PLAIN LOST. WINNER SCROLL. Tape: SCROLL WON.

The control never moved. Vertical intent went to the ScrollView because .gesture(DragGesture()) does not outrank scroll.

Mini-exercise

Swap PRIORITY to plain .gesture and PLAIN to .highPriorityGesture. Re-run. The rose card should be the one that can show a non-zero offset.

Challenges

1. Add a third card with .simultaneousGesture(DragGesture()) and photograph whether scroll and drag both fire.
2. Replace sequencing with simultaneous long-press + drag and show the scale pulse during the drag still.
3. Use .highPriorityGesture on PLAIN but only for horizontal drags (DragGesture that ignores dy) — vertical should still scroll.
4. Drive a real finger on device and confirm the scripted 72 pt / SCROLL WON labels match what you feel.
5. XCUITest: after -mode priority, assert static text contains 72 and WINNER PRIORITY.

Key Points

• Observed idle: both cards 0 pt.
• Observed arm: tape LONGPRESS, PRIORITY armed, still 0 pt.
• Observed priority drag: 72 pt, tape DRAG+72, WINNER PRIORITY.
• Observed plain conflict: 0 pt, WINNER SCROLL, tape SCROLL WON.
• .sequenced(before:) arms a drag with a long-press.
• .highPriorityGesture beats ScrollView; plain .gesture often loses.
• The control is the same DragGesture with the priority modifier removed.
• If a handle inside a list will not move, check gesture priority before blaming DragGesture.

Next up: environment and preferences — values travelling down (Environment) and measurements travelling up (PreferenceKey) on one screen, both directions traced.