#! /usr/bin/python

#  (tested on Windows XP, with Python 2.7 and Tcl/Tk 8.5.2 built entirely
#  from sources; on Linux using Ubuntu 9.04 distributed packages -- Python
#  2.6.2)

#  Example of a scrolled list bulit from a custom widget
#
#  type1: an Entry field with a StringVar built-in
#  type2: another Entry field, without the built-in StringVar
#  frm: a Frame build from two type1's and one type2, with some Labels
#  testlist: a scrolling list of frm's
#  testcase: build a 3 high testlist with 10 frm's (scrollable)

#  Issues:
#
#    1. Moving the slider slightly gives jerky motion due to
#       redisplaying.  To reduce this I check for a small "moveto"
#       that doesn't change the displayed row and only set the
#       scrollbar (slider) without redisplaying the list elements.
#
#    2. on Linux, moving the slider on the scroll bar to the top
#       sometimes gives a negative "moveto", which I force to 0, or a
#       "moveto" greater than 1.0, which I force to 1.0.  This
#       doesn't happen on Windows.
#
#    3. on Windows, using "pack" as shown causes the root window to flash
#       quite a bit when scrolling (presumably due to the "grid_forget"s
#       briefly redisplaying the window with fewer rows.  This isn't
#       visible on Linux.  As a workaround on Windows I use a Canvas
#       which hides the flashing. 
#
#    4. (MOST SEVERE) On Windows, with or without the Canvas widget,
#       moving the slider slowly hits a glitch when row #7 would be
#       the top row displayed.  The slider jumps between a pair of
#       values (sometimes 0.56 and 0.7, sometimes other values),
#       causing the window to flash rapidly.  I cannot get the slider
#       to position row #7 at the top -- it jumps to row #8 or row #6
#       (or even lower).  This does not happen on Linux -- scrolling
#       is smooth, no glitches.

from Tkinter import *
import sys

class type1(Entry):
    def __init__(self,master, v='xxx'):
        self.v = StringVar()
        self.v.set(v)
        Entry.__init__(self, master, textvariable=self.v)

class type2(Entry):
    def __init__(self,master, **kw):
        Entry.__init__(self,master,**kw)

class frm(Frame):
    def __init__(self, master, **kw):
        Frame.__init__(self)
        self.x1 = type1(self,**kw)
        self.x1.pack(side=LEFT)
        self.fx2 = Frame(self)
        Label(self, text=' X2').pack(in_=self.fx2,side=LEFT)
        self.v2 = StringVar()
        self.v2.set('yy')
        self.x2 = type2(self,width=5,textvariable=self.v2)
        self.x2.pack(in_=self.fx2,side=LEFT)
        self.fx2.pack(side=LEFT)
        self.fx3 = Frame(self)
        Label(self,text=' X3').pack(in_=self.fx3,side=LEFT)
        self.x3 = type1(self, v='zzz')
        self.x3.pack(in_=self.fx3,side=LEFT)
        self.fx3.pack(side=LEFT)

class testlist(Frame):
    def __init__(self, master, maxdisp=3, **kw):
        Frame.__init__(self,master)
        self.sb = Scrollbar(self, command=self.scroll)
        self.sb.grid(in_=self,row=0,column=1,rowspan=maxdisp,sticky=N+S)
        self.maxdisp = maxdisp
        self.frms = [frm(self,**kw)]
        self.active = 0
        self.frms[0].grid(in_=self,row=0,column=0)
    def setsb(self,start,mv):
        dispfrac = self.maxdisp / float(len(self.frms))
        startfrac = float(start) / len(self.frms)
        if mv == None:
            self.sb.set(startfrac, min(1, startfrac+dispfrac))
        else:
            self.sb.set(mv, min(1, mv+dispfrac))
    def redisp(self, start, mv=None):
        for xx in self.frms[self.active:self.maxdisp+self.active]:
            xx.grid_forget()
        yy = 0
        for xx in self.frms[start:self.maxdisp+start]:
            xx.grid(in_=self,row=yy,column=0)
            yy += 1
        self.setsb(start,mv)
#        print start, startfrac, min(1, startfrac+dispfrac)
        self.active = start
    def addentry(self, **kw):
        self.frms.append(frm(self,**kw))
        #  perhaps move to the end of the list ?
        self.redisp(self.active)
    def scroll(self,*xx):
        op, cnt = xx[0], xx[1]
        mv = None
        if op == "scroll":
            if xx[2] == 'pages':
                amt = self.maxdisp * int(xx[1])
            else:
                amt = int(xx[1])
            newstart = self.active + amt
        else:
            mv = min(1.0,max(0.0,float(cnt)))
            newstart = int(len(self.frms) * mv)
            print cnt, mv, newstart
        newstart = min(newstart, len(self.frms) - self.maxdisp)
        newstart = max(0, newstart)
        if newstart <> self.active:
            self.redisp(newstart,mv=mv)
        else:
            self.setsb(newstart,mv)

def testcase(master):
    tt = testlist(master,v='1')
    for xx in range(2,11):
        tt.addentry(v=str(xx))
    return tt
    
if (__name__ == '__main__'):
    rr = Tk()
    try:
        arg1=sys.argv[1]
    except IndexError:
        arg1=None
    if arg1 == 'c':
        #  use Canvas
        cc=Canvas(rr,height=300,width=600)
        cc.pack()
        tt = testcase(cc)
        tt.place(x=10, y=10)
    else:
        # just pack into root
        tt = testcase(rr)
        tt.pack()
    rr.mainloop()