Touch, Gestures & Files

Every node can hear touch, gestures and files dropped on it, as handlers on its handlers: mapping. Each names a ViewModel method, which takes the event (or nothing). A disabled node hears none.

id: canvas
kind: Container
style: {width: 320, height: 240, background: surface_container}
handlers:
  on_tap: tapped
  on_pan: panned
  on_pinch: pinched
  on_file_drop: opened

Handler	Event	The event's fields
on_tap	a quick touch and lift	count (2 for a double tap)
on_long_press	a finger held in place
on_pan	a finger dragged	phase (began, changed, ended, cancelled), delta_x, delta_y, total_x, total_y; on ended also velocity_x, velocity_y
on_pinch	two fingers, or a trackpad pinch	phase, scale, scale_delta (the step to apply)
on_touch_start, on_touch_move, on_touch_end, on_touch_cancel	each finger	pointer_id
on_file_hover, on_file_hover_cancel, on_file_drop	files dragged over, away from, or dropped on it	paths, and path for the first
on_link	a link in rich text was clicked	href

The first finger is also the pointer: a tap is a click, so an app written for the mouse works under a finger. When that finger starts to pan, the press is cancelled and the pan scrolls the scroll view under it, unless a node on the way has an on_pan, which takes the pan instead. Gestures bubble to ancestors, like clicks.

Files

on_file_hover is the moment to show a drop target and on_file_hover_cancel to hide it; on_file_drop receives the paths, all of a drop in one event. Reading the files is the app's.

class MainViewModel(ViewModel):
    def opened(self, event):
        for path in event.paths:
            self.documents.append(Path(path).read_text())

For a drop anywhere on the window, app.on_file_drop(handler). The OS gives no position to a file drag while it is over the window, so the node that hears it is the one under the pointer's last known place. A file drop doesn't work on Wayland.

Testing

window.simulate delivers all of these without a display: touch_start, touch_move, touch_end, trackpad_pinch, file_hover, file_drop and link. A tap or a pan is a sequence of touches.