Godot: ItemList can not scroll by dragging on the ItemList

[alexzheng]

Operating system or device, Godot version, GPU Model and driver (if graphics related):
godot 2.1
device iOS, Android

Issue description:

On touch screen device,
the ItemList can only scrolled by dragging the scroll bar.
When touch on the ItemList itself and drag, it can not scroll.
This is not the same as the list on touch screen.

Steps to reproduce:

Link to minimal example project:

[raymoo]

Similar to #8151, though not a duplicate.

[RKelln]

I am using this script to allow dragging on an ItemList. Use at your own risk:

extends ItemList

export(float) var drag_threshold = 5

onready var touch_enabled = OS.has_touchscreen_ui_hint()
onready var v_scroll = get_v_scroll()

var dragging = false
var pressed = false

# must be _input, as _gui_input has bugs, with no touch.pressed = false events
# see: https://github.com/godotengine/godot/issues/16761
func _input(event):
    if not visible:
        return

    if not touch_enabled:
        return

    if event is InputEventScreenDrag:
        accept_event()
        if event.speed == Vector2():
            # we're on a device and speed is broken
            # see: https://github.com/godotengine/godot/issues/3623
            event.speed = event.relative
        if abs(event.speed.y) >= drag_threshold:
            # scroll the list
            dragging = true
            v_scroll.value -= event.relative.y
        return

    if event is InputEventScreenTouch:
        if event.index == 0:
            accept_event()
            if dragging && event.pressed == false:
                # prints("end drag")
                dragging = false
                pressed = false
            else:
                if event.pressed && pressed == false:
                    # prints("touch start")
                    pressed = true
                    # TODO: prevent select highlight
                elif !event.pressed && pressed == true:
                    # prints("touch end and accept")
                    pressed = false
                    var ev = InputEventAction.new()
                    ev.action = "ui_accept"
                    ev.pressed = true
                    Input.parse_input_event(ev)

[AlexHolly]

Same with ScrollContainer, it works in Tree, see in FileDialog

[tavurth]

I use this script which is quite simple and should fill most use cases:

extends ItemList

onready var Scroller: VScrollBar = self.get_v_scroll()

func _ready():
    self.connect("gui_input", self, "_on_gui_input")

func _on_gui_input(event: InputEvent):
    if event is InputEventScreenDrag:
        self.Scroller.value -= event.relative.y

I then have a "Go" (confirmation) button which appears whenever any item in the list is selected. That way I can scroll as much as I want without closing the window.