bootstack.ScrollView#

class bootstack.ScrollView(*, scroll_direction='both', scrollbar_visibility='always', scrollbar_variant='default', autohide_delay=1000, height=None, width=None, show_border=False, padding=None, parent=None, **kwargs)#

Bases: FlexContainer

A canvas-based scrollable container.

Place children inside the context block; they are laid out vertically inside the scrollable area. Mouse-wheel scrolling is automatically enabled for all descendants.

Parameters:

scroll_direction (Literal['vertical', 'horizontal', 'both']) – Which axis to scroll. Defaults to 'both'.
scrollbar_visibility (Literal['always', 'never', 'hover', 'scroll']) – When scrollbars appear — 'always' (default), 'never', 'hover' (appears on mouse enter), or 'scroll' (auto-hides after autohide_delay ms of inactivity).
scrollbar_variant (ScrollbarVariant) – Scrollbar style — 'default' (standard rounded bar) or 'thin' (slim square bar).
autohide_delay (int) – Milliseconds before scrollbars hide in 'scroll' mode. Defaults to 1000.
height (int | None) – Fixed height of the viewport in pixels. When set, the canvas is pinned to this height regardless of content size. Required for vertical scrolling unless the parent already constrains the height. Defaults to None.
width (int | None) – Fixed width of the viewport in pixels. Pins the canvas width, similar to height=. Defaults to None.
show_border (bool) – Draw a 1 px border around the ScrollView frame. Defaults to False.
padding (Padding | None) – Space in pixels between the border and the canvas. Defaults to None (no padding).
parent (Any) – Override the context-stack parent.
**kwargs (Any) – Layout placement options applied by the parent container — fill, expand, anchor, margin, row, column, sticky. See Arranging Widgets.

property is_attached: bool#

Whether the widget is currently placed in its layout.

True while the widget occupies space in its parent; False after detach (or before it has ever been placed). A detached widget keeps its state and can be returned to the layout with attach.

property schedule: Schedule#

Scheduler tied to this widget’s lifetime.

All jobs are automatically cancelled when the widget is destroyed. First access creates the Schedule instance; subsequent accesses return the same instance.

Usage:

self.schedule.delay(500, callback)
self.schedule.every(1000, tick)
job = self.schedule.idle(refresh)
job.cancel()

property scroll_position: tuple[float, float]#

Current scroll position as (y, x) fractions.

Each value is the fraction of the content that lies above (y) or to the left (x) of the viewport’s top-left corner. (0.0, 0.0) means scrolled fully to the top-left. As you scroll toward the end the value grows toward 1.0 but does not reach it while content fills the viewport (it tops out at roughly 1.0 minus the visible fraction) — only an axis whose content is shorter than the viewport reads 0.0. Read this inside an on_scroll handler to get the new position:

sv.on_scroll(lambda e: print(e.y, e.x))

attach(**kwargs)#

Return a detached widget to its layout, optionally moving it.

With no arguments, restores the widget to exactly where detach took it from. Any layout kwargs accepted by the original placement (e.g. fill, expand, anchor, sticky, margin) override the stored options. For stacked widgets, index= sets the position among the currently attached siblings (or pass an explicit before=/after= sibling); without one, the snapshotted position is used.

Calling attach on a widget that is already attached moves it (the kwargs are re-applied). Fires on_attach.

Parameters:: **kwargs (Any) – Layout placement options to override for this placement.
Raises:: ParentResolutionError – If the widget was never placed in a layout.

capture(path, *, inset=0, settle=0.1)#

Save a picture of this widget to an image file.

Captures the area this widget occupies on screen — one widget, a whole window, or the entire application, depending on what you call it on. The file extension selects the format, so .png, .jpg, and .pdf all work.

The widget has to be visible. A capture reads pixels from the display, so the window is brought to the front first and a hidden or detached widget cannot be captured at all. Any always-on-top setting the window already had is left as it was found.

Pair it with a save dialog to let the user choose where it goes:

import bootstack as bs

def on_export():
    chosen = bs.ask_save_file(initial_file="dashboard.png")
    if chosen:
        app.capture(chosen)

Parameters:

path (str | Path) – Where to write the image. Missing parent folders are created, and the extension chooses the format.
inset (int) – Pixels to trim from every edge, zero or more. Use 2 on a whole window to drop the native border artifact.
settle (float) – Seconds to let the desktop finish repainting before the pixels are read. The default covers the common case of a dialog closing just beforehand. The interface pauses for this long, so a second click on the control that started the capture waits its turn rather than starting an overlapping one.

Returns:

The path that was written.

Raises:

BootstackError – If the widget is not visible on screen or has been scrolled out of view, if inset is negative, if no capture backend is available, or if the file cannot be written.

Return type:

Path

Added in version 0.3.0.

destroy()#

Destroy the widget and release the resources it holds.

Removes the widget from its parent, destroys its children, and cancels any pending or repeating jobs on its schedule. After this the widget must not be used again. Destroying a container destroys everything inside it.

detach()#

Remove the widget from its layout without destroying it.

The widget stops occupying space but keeps its state, children, and event bindings, ready to be returned with attach. The current position is snapshotted so a plain attach() restores it exactly — for stacked siblings this is the index among the currently attached siblings, so detaching other siblings first shifts that index.

Calling detach on a widget that is already detached, or one that was never placed in a layout, does nothing. Fires on_detach.

disable_scrolling()#

Disable mouse-wheel scrolling on the canvas and all children.

emit(event, *, data=None)#

Fire a named event on this widget, as if it produced the event itself.

This is how a composite widget surfaces high-level activity to its listeners, and the generic counterpart to the on_*() shorthands for firing events that have no dedicated method.

It is meant for the framework’s own events — 'change', 'select', 'input' and the rest of the data-carrying names. A handler registered through on() or an on_<event>() shorthand receives what is emitted.

Names that map onto a native event instead ('click', 'focus', 'blur', 'submit', …) are a different matter: emitting one asks the toolkit to deliver a real input event, which carries no payload and can reach handlers the widget installed for its own use. Emitting those is not a way to notify listeners, and a listener bound through on() may not see it. Drive the widget through its properties and methods instead.

Parameters:

event (str) – The event name, unprefixed — the same name you pass to on() or an on_<event>() shorthand (e.g. 'change', 'select').
data (Any) – The payload delivered to handlers. Pass the matching payload dataclass from bootstack.events — the same object an on_<event>() handler receives.

Example

from bootstack.events import ChangeEvent

field.emit("change", data=ChangeEvent(value=new_value))

enable_scrolling()#

Enable mouse-wheel scrolling on the canvas and all children.

guide_layout(child, **layout_kw)#

Place child into this container’s flow and snapshot its placement.

on(event, handler=None)#

Bind handler to event, or return a composable Stream.

With a handler — binds immediately and returns a Subscription:

sub = widget.on("change", handler)
sub.cancel()

Without a handler — returns a Stream for operator chaining. The Tk binding is created lazily when .listen() is called:

sub = widget.on("change").debounce(300).listen(handler)
sub.cancel()

Parameters:

event (str) – Event name (e.g. "change", "click").
handler (Callable[[Any], Any] | None) – Optional callback. If omitted, a Stream is returned.

Returns:

Subscription when a handler is provided; Stream otherwise.

Return type:

Stream | Subscription

on_attach(handler=None)#

Register a callback fired when the widget enters the layout.

Fires each time the widget becomes visible in its parent — on initial placement and on every attach. Pair it with on_detach to keep per-visibility resources (timers, observers) tied to the widget’s presence on screen. The handler receives a curated Event.

Parameters:: handler (Callable[[Event], Any] | None) – Called when the widget is attached. Omit to get a composable Stream.
Returns:: A cancellable Subscription when a handler is given, otherwise a Stream.
Return type:: Stream | Subscription

on_destroy(handler=None)#

Register a callback fired when the widget is destroyed.

Fires once, as the widget is torn down — the place to release resources the widget owns that aren’t cleaned up automatically (file handles, observers, external subscriptions). The handler receives a curated Event.

Parameters:: handler (Callable[[Event], Any] | None) – Called as the widget is destroyed. Omit to get a composable Stream.
Returns:: A cancellable Subscription when a handler is given, otherwise a Stream.
Return type:: Stream | Subscription

on_detach(handler=None)#

Register a callback fired when the widget leaves the layout.

Fires each time the widget stops occupying space in its parent — on detach and when an ancestor hides it. Pair it with on_attach to release per-visibility resources. The handler receives a curated Event.

Parameters:: handler (Callable[[Event], Any] | None) – Called when the widget is detached. Omit to get a composable Stream.
Returns:: A cancellable Subscription when a handler is given, otherwise a Stream.
Return type:: Stream | Subscription

on_scroll() → Stream#

on_scroll(handler: Callable[[ScrollEvent], Any]) → Subscription

Register a callback fired whenever the viewport position changes.

Fires on mouse-wheel scrolls, programmatic scroll_to_* / yview_moveto calls, and keyboard scrolling (arrow keys / Page Up / Page Down / Home / End when the canvas has focus from a click).

Parameters:: handler (Callable[[ScrollEvent], Any] | None) – Called with a ScrollEvent carrying y (vertical fraction, 0.0–1.0) and x (horizontal fraction). Omit to get a composable Stream.
Returns:: A cancellable Subscription when a handler is given, otherwise a Stream.
Return type:: Stream | Subscription