import tkinter as tk
import platform

# ************************
# Scrollable Frame Class
# ************************
class ScrollFrame(tk.Frame):
    def __init__(self, parent):
        super().__init__(parent) # create a frame (self)

        self.canvas = tk.Canvas(self, borderwidth=0, background="#ffffff")          #place canvas on self
        self.viewPort = tk.Frame(self.canvas, background="#ffffff")                    #place a frame on the canvas, this frame will hold the child widgets 
        self.vsb = tk.Scrollbar(self, orient="vertical", command=self.canvas.yview) #place a scrollbar on self 
        self.canvas.configure(yscrollcommand=self.vsb.set)                          #attach scrollbar action to scroll of canvas

        self.vsb.pack(side="right", fill="y")                                       #pack scrollbar to right of self
        self.canvas.pack(side="left", fill="both", expand=True)                     #pack canvas to left of self and expand to fil
        self.canvas_window = self.canvas.create_window((4,4), window=self.viewPort, anchor="nw",            #add view port frame to canvas
                                  tags="self.viewPort")

        self.viewPort.bind("<Configure>", self.onFrameConfigure)                       #bind an event whenever the size of the viewPort frame changes.
        self.canvas.bind("<Configure>", self.onCanvasConfigure)                       #bind an event whenever the size of the canvas frame changes.
            
        self.viewPort.bind('<Enter>', self.onEnter)                                 # bind wheel events when the cursor enters the control
        self.viewPort.bind('<Leave>', self.onLeave)                                 # unbind wheel events when the cursorl leaves the control

        self.onFrameConfigure(None)                                                 #perform an initial stretch on render, otherwise the scroll region has a tiny border until the first resize

    def onFrameConfigure(self, event):                                              
        '''Reset the scroll region to encompass the inner frame'''
        print("onFrameConfig")
        print(event)
        print(self.viewPort, id(self.viewPort))
        print("-----")
        print("scrollregiion : ", self.canvas.bbox("all"))
        self.canvas.configure(scrollregion=self.canvas.bbox("all"))                 #whenever the size of the frame changes, alter the scroll region respectively.

    def onCanvasConfigure(self, event):
        '''Reset the canvas window to encompass inner frame when required'''
        print("Canvas config")
        print(event)
        canvas_width = event.width
        self.canvas.itemconfig(self.canvas_window, width = canvas_width)            #whenever the size of the canvas changes alter the window region respectively.

    def onMouseWheel(self, event):                                                  # cross platform scroll wheel event
        #print("onMouseWheel")
        #print(event)
        if platform.system() == 'Windows':

            self.canvas.yview_scroll(int(-1* (event.delta/120)), "units")
        elif platform.system() == 'Darwin':
            self.canvas.yview_scroll(int(-1 * event.delta), "units")
        else:
            if event.num == 4:
                self.canvas.yview_scroll( -1, "units" )
            elif event.num == 5:
                self.canvas.yview_scroll( 1, "units" )
    
    def onEnter(self, event):                                                       # bind wheel events when the cursor enters the control
        #print("onEnter")
        #print(event)
        if platform.system() == 'Linux':
            self.canvas.bind_all("<Button-4>", self.onMouseWheel)
            self.canvas.bind_all("<Button-5>", self.onMouseWheel)
        else:
            self.canvas.bind_all("<MouseWheel>", self.onMouseWheel)

    def onLeave(self, event):                                                       # unbind wheel events when the cursorl leaves the control
        #print("onLeave")
        #print(event)
        if platform.system() == 'Linux':
            self.canvas.unbind_all("<Button-4>")
            self.canvas.unbind_all("<Button-5>")
        else:
            self.canvas.unbind_all("<MouseWheel>")



# ********************************
# Example usage of the above class
# ********************************

class Example(tk.Frame):
    def __init__(self, root):

        tk.Frame.__init__(self, root)
        self.scrollFrame = ScrollFrame(self) # add a new scrollable frame.
        
        # Now add some controls to the scrollframe. 
        # NOTE: the child controls are added to the view port (scrollFrame.viewPort, NOT scrollframe itself)
        for row in range(100):
            a = row
            tk.Label(self.scrollFrame.viewPort, text="%s" % row, width=3, borderwidth="1", 
                     relief="solid").grid(row=row, column=0)
            t="this is the second column for row %s" %row
            tk.Button(self.scrollFrame.viewPort, text=t, command=lambda x=a: self.printMsg("Hello " + str(x))).grid(row=row, column=1)

        # when packing the scrollframe, we pack scrollFrame itself (NOT the viewPort)
        self.scrollFrame.pack(side="top", fill="both", expand=True)
    
    def printMsg(self, msg):
        print(msg)

if __name__ == "__main__":
    root=tk.Tk()
    Example(root).pack(side="top", fill="both", expand=True)
    root.mainloop()