如何指示 urwid 列表框的项目数多于当前显示的项目数？

有没有办法向用户显示 urwid 列表框在显示部分上方/下方有其他项目？

我正在考虑类似滚动条的东西，它可以显示条目的数量。

或者列表框顶部/底部的单独栏。

如果这个行为无法实现，有哪些方法可以实现这个通知？

在我的研究过程中，我发现这个问题 https://stackoverflow.com/questions/48737120/how-do-i-determine-the-number-of-visible-items-in-a-listbox-with-urwid，最终试图实现相同的目标。 给出的答案似乎是检查所有元素是否可见。不幸的是，如果由于终端大小未调整而随时隐藏某些元素，则此功能将失去其功能。

我想我已经找到了第二个可视化概念的实现（列表框顶部和底部的栏）。

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

import urwid

ENTRIES = [letter for letter in "abcdefghijklmnopqrstuvwxyz"]

PALETTE = [
    ("notifier_active",   "dark cyan",  "light gray"),
    ("notifier_inactive", "black", "dark gray"),
    ("reveal_focus",      "black",      "dark cyan", "standout")
]


class MyListBox(urwid.ListBox):
    def __init__(self, body, on_focus_change=None):
        super().__init__(body)

        self.on_focus_change = on_focus_change

    # Overriden
    def change_focus(self, size, position, offset_inset=0, coming_from=None, cursor_coords=None, snap_rows=None):
        super().change_focus(size,
                             position,
                             offset_inset,
                             coming_from,
                             cursor_coords,
                             snap_rows)

        # Implement a hook to be able to deposit additional logic
        if self.on_focus_change != None:
            self.on_focus_change(size,
                                 position,
                                 offset_inset,
                                 coming_from,
                                 cursor_coords,
                                 snap_rows)


class App(object):
    def __init__(self, entries):
        # Get terminal dimensions
        terminal_cols, terminal_rows = urwid.raw_display.Screen().get_cols_rows()
        list_rows = (terminal_rows - 2) if (terminal_rows > 7) else 5       
        # (available_rows - notifier_rows) OR my preferred minimum size

        # At the beginning, "top" is always visible
        self.notifier_top = urwid.AttrMap(urwid.Text('^', align="center"),
                                          "notifier_inactive")

        # Determine presentation depending on size and number of elements
        self.notifier_bottom = urwid.AttrMap(urwid.Text('v', align="center"),
                                             "notifier_inactive" if (len(entries) <= list_rows) else "notifier_active")

        contents = [urwid.AttrMap(urwid.Button(entry), "", "reveal_focus")
                    for entry in entries]

        self.listbox = MyListBox(urwid.SimpleFocusListWalker(contents),
                                 self.update_notifiers)                   # Pass the hook

        master_pile = urwid.Pile([
            self.notifier_top,
            urwid.BoxAdapter(self.listbox, list_rows),
            self.notifier_bottom,
        ])

        widget = urwid.Filler(master_pile,
                              'top')

        self.loop = urwid.MainLoop(widget,
                                   PALETTE,
                                   unhandled_input=self.handle_input)

    # Implementation for hook
    def update_notifiers(self, size, position, offset_inset, coming_from, cursor_coords, snap_rows):
        # which ends are visible? returns "top", "bottom", both or neither.
        result = self.listbox.ends_visible(size)

        if ("top" in result) and ("bottom" in result):
            self.notifier_top.set_attr_map({None:"notifier_inactive"})
            self.notifier_bottom.set_attr_map({None:"notifier_inactive"})
        elif "top" in result:
            self.notifier_top.set_attr_map({None:"notifier_inactive"})
            self.notifier_bottom.set_attr_map({None:"notifier_active"})
        elif "bottom" in result:
            self.notifier_top.set_attr_map({None:"notifier_active"})
            self.notifier_bottom.set_attr_map({None:"notifier_inactive"})
        else:
            self.notifier_top.set_attr_map({None:"notifier_active"})
            self.notifier_bottom.set_attr_map({None:"notifier_active"})

    def handle_input(self, key):
        if key in ('q', 'Q', 'esc'):
            self.exit()

    def start(self):
        self.loop.run()

    def exit(self):
        raise urwid.ExitMainLoop()


if __name__ == '__main__':
    app = App(ENTRIES)
    app.start()

基本上，我创建了一个子类urwid.Listbox并覆盖它的change_focus()添加钩子的方法。显然，当焦点发生变化时，该方法会在内部被调用。

实际逻辑使用的结果ends_visible()方法，它返回列表框当前可见的末端（顶部、底部、两者或都不返回）。根据这一点，我修改了两个周围的呈现方式urwid.Text元素。

该代码生成以下 TUI：

我还编写了代码的变体，它基于原始规范：

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

import urwid

HEADERS = ["column 1",
           "column 2",
           "column 3",
           "column 4"]

ENTRIES = [["{}1".format(letter),
            "{}2".format(letter),
            "{}3".format(letter),
            "{}4".format(letter)] for letter in "abcdefghijklmnopqrstuvwxyz"]

PALETTE = [
    ("column_headers", "white, bold", ""),
    ("notifier_active",   "dark cyan",  "light gray"),
    ("notifier_inactive", "black", "dark gray"),
    ("reveal_focus",      "black",      "dark cyan", "standout")
]


class SelectableRow(urwid.WidgetWrap):
    def __init__(self, contents, on_select=None):
        self.contents = contents
        self.on_select = on_select

        self._columns = urwid.Columns([urwid.Text(c) for c in contents])
        self._focusable_columns = urwid.AttrMap(self._columns, '', 'reveal_focus')

        super(SelectableRow, self).__init__(self._focusable_columns)

    def selectable(self):
        return True

    def update_contents(self, contents):
        # update the list record inplace...
        self.contents[:] = contents

        # ... and update the displayed items
        for t, (w, _) in zip(contents, self._columns.contents):
            w.set_text(t)

    def keypress(self, size, key):
        if self.on_select and key in ('enter',):
            self.on_select(self)
        return key

    def __repr__(self):
        return '%s(contents=%r)' % (self.__class__.__name__, self.contents)


class MyListBox(urwid.ListBox):
    def __init__(self, body, on_focus_change=None):
        super().__init__(body)

        self.on_focus_change = on_focus_change

    # Overriden
    def change_focus(self, size, position, offset_inset=0, coming_from=None, cursor_coords=None, snap_rows=None):
        super().change_focus(size,
                             position,
                             offset_inset,
                             coming_from,
                             cursor_coords,
                             snap_rows)

        # Implement a hook to be able to deposit additional logic
        if self.on_focus_change != None:
            self.on_focus_change(size,
                                 position,
                                 offset_inset,
                                 coming_from,
                                 cursor_coords,
                                 snap_rows)


class App(object):
    def __init__(self, entries):
        # Get terminal dimensions
        terminal_cols, terminal_rows = urwid.raw_display.Screen().get_cols_rows()
        list_rows = (terminal_rows - 6) if (terminal_rows > 11) else 5       
        # (available_rows - divider_rows - column_headers_row - notifier_rows) OR my preferred minimum size

        column_headers = urwid.AttrMap(urwid.Columns([urwid.Text(c) for c in HEADERS]),
                                       "column_headers")

        # At the beginning, "top" is always visible
        self.notifier_top = urwid.AttrMap(urwid.Text('^', align="center"),
                                          "notifier_inactive")

        # Determine presentation depending on size and number of elements
        self.notifier_bottom = urwid.AttrMap(urwid.Text('v', align="center"),
                                             "notifier_inactive" if (len(entries) <= list_rows) else "notifier_active")

        contents = [SelectableRow(entry) for entry in entries]

        self.listbox = MyListBox(urwid.SimpleFocusListWalker(contents),
                                 self.update_notifiers)                    # Pass the hook

        master_pile = urwid.Pile([
            urwid.Divider(u'─'),
            column_headers,
            urwid.Divider(u'─'),
            self.notifier_top,
            urwid.BoxAdapter(self.listbox, list_rows),
            self.notifier_bottom,
            urwid.Divider(u'─'),
        ])

        widget = urwid.Filler(master_pile,
                              'top')

        self.loop = urwid.MainLoop(widget,
                                   PALETTE,
                                   unhandled_input=self.handle_input)

    # Implementation for hook
    def update_notifiers(self, size, position, offset_inset, coming_from, cursor_coords, snap_rows):
        # which ends are visible? returns "top", "bottom", both or neither.
        result = self.listbox.ends_visible(size)

        if ("top" in result) and ("bottom" in result):
            self.notifier_top.set_attr_map({None:"notifier_inactive"})
            self.notifier_bottom.set_attr_map({None:"notifier_inactive"})
        elif "top" in result:
            self.notifier_top.set_attr_map({None:"notifier_inactive"})
            self.notifier_bottom.set_attr_map({None:"notifier_active"})
        elif "bottom" in result:
            self.notifier_top.set_attr_map({None:"notifier_active"})
            self.notifier_bottom.set_attr_map({None:"notifier_inactive"})
        else:
            self.notifier_top.set_attr_map({None:"notifier_active"})
            self.notifier_bottom.set_attr_map({None:"notifier_active"})

    def handle_input(self, key):
        if key in ('q', 'Q', 'esc'):
            self.exit()

    def start(self):
        self.loop.run()

    def exit(self):
        raise urwid.ExitMainLoop()


if __name__ == '__main__':
    app = App(ENTRIES)
    app.start()

唯一真正的区别是，我使用的实例SelectableRow代替urwid.Button. (SelectableRow被取自用户 elias 的回答 https://stackoverflow.com/questions/52106244/how-do-you-combine-multiple-tui-forms-to-write-more-complex-applications#answer-52174629.)

这是相应的 TUI：