Why doesn't the window update in curses?

问题

I took this nice example of a simple curses application with a list. I wanted to make it scrollable, so I changed the part of the list that gets shown. However, I can scroll down and back up, but the contents shown doesn't change (only the highlighted line, not the lines shown).

What am I doing wrong?

MVCE

#!/usr/bin/env python

import curses
from curses import panel


class Menu(object):
    def __init__(self, items, stdscreen):
        self.window = stdscreen.subwin(0, 0)
        self.window.keypad(1)
        self.panel = panel.new_panel(self.window)
        self.panel.hide()
        panel.update_panels()

        self.position = 0
        self.items = items

    def navigate(self, n):
        self.position += n
        if self.position < 0:
            self.position = 0
        elif self.position >= len(self.items):
            self.position = len(self.items) - 1

    def display(self):
        self.panel.top()
        self.panel.show()
        self.window.clear()

        while True:
            self.window.refresh()
            curses.doupdate()
            start = 0

            # The next 3 lines seem not to work as intended
            while start + (curses.LINES - 1) < self.position:
                start += curses.LINES
            for index, item in enumerate(self.items[start:curses.LINES - 1], start=start):
                if index == self.position:
                    mode = curses.A_REVERSE
                else:
                    mode = curses.A_NORMAL

                msg = "%d. %s" % (index, item[0])
                self.window.addstr(1 + index, 1, msg, mode)

            key = self.window.getch()

            if key in [curses.KEY_ENTER, ord("\n"), curses.KEY_RIGHT]:
                self.items[self.position][1]()

            elif key == curses.KEY_UP:
                self.navigate(-1)

            elif key == curses.KEY_DOWN:
                self.navigate(1)
            elif key == curses.KEY_LEFT:
                break

        self.window.clear()
        self.panel.hide()
        panel.update_panels()
        curses.doupdate()


class MyApp(object):
    def __init__(self, stdscreen):
        self.screen = stdscreen
        curses.curs_set(0)

        submenu_items = [("beep", curses.beep), ("flash", curses.flash)]
        submenu = Menu(submenu_items, self.screen)

        main_menu_items = [
            ("beep", curses.beep),
            ("flash", curses.flash),
            ("submenu", submenu.display),
        ]
        for i in range(200):
            main_menu_items.append((f"flash {i}", curses.flash))
        main_menu = Menu(main_menu_items, self.screen)
        main_menu.display()


if __name__ == "__main__":
    curses.wrapper(MyApp)

回答1:

Basically that's because you're not updating the upper limit on the slice used in this loop:

for index, item in enumerate(self.items[start:curses.LINES - 1], start=start):

Here's a better version

MVCE

#!/usr/bin/env python

import curses
from curses import panel


class Menu(object):
    def __init__(self, items, stdscreen):
        self.window = stdscreen.subwin(0, 0)
        self.window.keypad(1)
        self.panel = panel.new_panel(self.window)
        self.panel.hide()
        panel.update_panels()

        self.position = 0
        self.items = items

    def navigate(self, n):
        self.position += n
        if self.position < 0:
            self.position = 0
        elif self.position >= len(self.items):
            self.position = len(self.items) - 1

    def display(self):
        self.panel.top()
        self.panel.show()
        self.window.clear()

        while True:
            start = 0
            self.window.clear()

            while start + (curses.LINES - 1) < self.position:
                start += curses.LINES
            myrow = self.position - start
            mycol = 0
            for index, item in enumerate(self.items[start:start + curses.LINES - 1], start=start):
                if index == self.position:
                    mode = curses.A_REVERSE
                else:
                    mode = curses.A_NORMAL

                msg = "%d. %s" % (index, item[0])
                self.window.addstr(index - start, 0, msg, mode)
                if index == self.position:
                    (myrow, mycol) = self.window.getyx()

            self.window.move(myrow, mycol)
            key = self.window.getch()

            if key in [curses.KEY_ENTER, ord("\n"), curses.KEY_RIGHT]:
                self.items[self.position][1]()

            elif key == curses.KEY_UP:
                self.navigate(-1)

            elif key == curses.KEY_DOWN:
                self.navigate(1)
            elif key == curses.KEY_LEFT:
                break

        self.window.clear()
        self.panel.hide()
        panel.update_panels()
        curses.doupdate()


class MyApp(object):
    def __init__(self, stdscreen):
        self.screen = stdscreen
        curses.curs_set(1)

        submenu_items = [("beep", curses.beep), ("flash", curses.flash)]
        submenu = Menu(submenu_items, self.screen)

        main_menu_items = [
            ("beep", curses.beep),
            ("flash", curses.flash),
            ("submenu", submenu.display),
        ]
        for i in range(200):
            main_menu_items.append((f"flash {i}", curses.flash))
        main_menu = Menu(main_menu_items, self.screen)
        main_menu.display()


if __name__ == "__main__":
    curses.wrapper(MyApp)

来源：https://stackoverflow.com/questions/61364148/why-doesnt-the-window-update-in-curses