Touchscreen scrolling Tkinter Python

Question

I am making a kiosk app for a raspberry pi in python with a 7 inch touchscreen. Everything works well and now, I am trying to make the scroll works like it does on touchscreens. I know that raspbian haven't got a properly touch interface, so, every touch on the screen work as a mouse-click, and if I move my finger touching the screen, works like the drag function.

To make this on python I use my modified version code of this Vertical Scrolled Frame using canvas and I need to add events binding <ButtonPress-1> and <B1-Motion>.

<ButtonPress-1> might save the y position of the click and enable the bind_all function for <B1-Motion>.

<B1-Motion> might set the scroll setting up or down the differrence between the y value saved by <ButtonPress-1> and the event.y of this event.

<ButtonRelease-1> might disable the bind_all function with <unbind_all> of the scroll.

My added code of the events is this, but I don't know how to make it work properly the .yview function of the canvas to make my function works as desired.

def moving(event):
    #In this part I don't know how to make my effect
    self.canvas.yview('scroll',event.y,"units")

def clicked(event):
    global initialy
    initialy = event.y
    self.canvas.bind_all('<B1-Motion>', moving)

def released(event):
    self.canvas.unbind_all('<B1-Motion>')

self.canvas.bind_all('<ButtonPress-1>',clicked)
self.canvas.bind_all('<ButtonRelease-1>', released)

Answer 1

Taking Saad's code as a base, I have modified it to make it work on every S.O. (win, linux,mac) using yview_moveto and I have applied some modifications as I explain here.

EDIT: I have edited the code to show the complete class.

class VerticalScrolledFrame(Frame):
    """A pure Tkinter scrollable frame that actually works!
    * Use the 'interior' attribute to place widgets inside the scrollable frame
    * Construct and pack/place/grid normally
    * This frame only allows vertical scrolling

    """
    def __init__(self, parent, bg,*args, **kw):
        Frame.__init__(self, parent, *args, **kw)

        # create a canvas object and a vertical scrollbar for scrolling it

        canvas = Canvas(self, bd=0, highlightthickness=0,bg=bg)
        canvas.pack(side=LEFT, fill=BOTH, expand=TRUE)

        # reset the view
        canvas.xview_moveto(0)
        canvas.yview_moveto(0)

        self.canvasheight = 2000

        # create a frame inside the canvas which will be scrolled with it
        self.interior = interior = Frame(canvas,height=self.canvasheight,bg=bg)
        interior_id = canvas.create_window(0, 0, window=interior,anchor=NW)

        # track changes to the canvas and frame width and sync them,
        # also updating the scrollbar
        def _configure_interior(event):
            # update the scrollbars to match the size of the inner frame
            size = (interior.winfo_reqwidth(), interior.winfo_reqheight())
            canvas.config(scrollregion="0 0 %s %s" % size)
            if interior.winfo_reqwidth() != canvas.winfo_width():
                # update the canvas's width to fit the inner frame
                canvas.config(width=interior.winfo_reqwidth())
        interior.bind('<Configure>', _configure_interior)

        def _configure_canvas(event):
            if interior.winfo_reqwidth() != canvas.winfo_width():
                # update the inner frame's width to fill the canvas
                canvas.itemconfigure(interior_id, width=canvas.winfo_width())
        canvas.bind('<Configure>', _configure_canvas)

        self.offset_y = 0
        self.prevy = 0
        self.scrollposition = 1

        def on_press(event):
            self.offset_y = event.y_root
            if self.scrollposition < 1:
                self.scrollposition = 1
            elif self.scrollposition > self.canvasheight:
                self.scrollposition = self.canvasheight
            canvas.yview_moveto(self.scrollposition / self.canvasheight)

        def on_touch_scroll(event):
            nowy = event.y_root

            sectionmoved = 15
            if nowy > self.prevy:
                event.delta = -sectionmoved
            elif nowy < self.prevy:
                event.delta = sectionmoved
            else:
                event.delta = 0
            self.prevy= nowy

            self.scrollposition += event.delta
            canvas.yview_moveto(self.scrollposition/ self.canvasheight)

        self.bind("<Enter>", lambda _: self.bind_all('<Button-1>', on_press), '+')
        self.bind("<Leave>", lambda _: self.unbind_all('<Button-1>'), '+')
        self.bind("<Enter>", lambda _: self.bind_all('<B1-Motion>', on_touch_scroll), '+')
        self.bind("<Leave>", lambda _: self.unbind_all('<B1-Motion>'), '+')

Answer 2

I modified the VerticalScrolledFrame with few lines of code which does scroll how you want. I tested the code with the VerticalScrolledFrame and it works fine with the mouse. Add the below code to the VerticalScrolledFrame.

self.offset_y = 0
def on_press(evt):
    self.offset_y = evt.y_root

def on_touch_scroll(evt): 
    if evt.y_root-self.offset_y<0: 
        evt.delta = -1
    else: 
        evt.delta = 1
    # canvas.yview_scroll(-1*(evt.delta), 'units') # For MacOS
    canvas.yview_scroll( int(-1*(evt.delta/120)) , 'units') # For windows

self.bind("<Enter>", lambda _: self.bind_all('<Button-1>', on_press), '+')
self.bind("<Leave>", lambda _: self.unbind_all('<Button-1>'), '+')
self.bind("<Enter>", lambda _: self.bind_all('<B1-Motion>', on_touch_scroll), '+')
self.bind("<Leave>", lambda _: self.unbind_all('<B1-Motion>'), '+')

I hope you can find this useful.