# Scale (Python)

Marta Maria Casetti
mmcasetti@gmail.com 2012
A slider widget for selecting a value from a range
Mario Blättermann
mario.blaettermann@gmail.com 2011, 2013, 2016, 2018, 2021

# Scale

Slide the scales!

# Code, der zum Generieren dieses Beispiels verwendet wurde

from gi.repository import Gtk import sys

class MyWindow(Gtk.ApplicationWindow):

def __init__(self, app): Gtk.Window.__init__(self, title="Scale Example", application=app) self.set_default_size(400, 300) self.set_border_width(5)

# two adjustments (initial value, min value, max value, # step increment - press cursor keys to see!, # page increment - click around the handle to see!, # page size - not used here) ad1 = Gtk.Adjustment(0, 0, 100, 5, 10, 0) ad2 = Gtk.Adjustment(50, 0, 100, 5, 10, 0)

# an horizontal scale self.h_scale = Gtk.Scale( orientation=Gtk.Orientation.HORIZONTAL, adjustment=ad1) # of integers (no digits) self.h_scale.set_digits(0) # that can expand horizontally if there is space in the grid (see # below) self.h_scale.set_hexpand(True) # that is aligned at the top of the space allowed in the grid (see # below) self.h_scale.set_valign(Gtk.Align.START)

# we connect the signal "value-changed" emitted by the scale with the callback # function scale_moved self.h_scale.connect("value-changed", self.scale_moved)

# a vertical scale self.v_scale = Gtk.Scale( orientation=Gtk.Orientation.VERTICAL, adjustment=ad2) # that can expand vertically if there is space in the grid (see below) self.v_scale.set_vexpand(True)

# we connect the signal "value-changed" emitted by the scale with the callback # function scale_moved self.v_scale.connect("value-changed", self.scale_moved)

# a label self.label = Gtk.Label() self.label.set_text("Move the scale handles...")

# a grid to attach the widgets grid = Gtk.Grid() grid.set_column_spacing(10) grid.set_column_homogeneous(True) grid.attach(self.h_scale, 0, 0, 1, 1) grid.attach_next_to( self.v_scale, self.h_scale, Gtk.PositionType.RIGHT, 1, 1) grid.attach(self.label, 0, 1, 2, 1)

self.add(grid)

# any signal from the scales is signaled to the label the text of which is # changed def scale_moved(self, event): self.label.set_text("Horizontal scale is " + str(int(self.h_scale.get_value())) + "; vertical scale is " + str(self.v_scale.get_value()) + ".")

class MyApplication(Gtk.Application):

def __init__(self): Gtk.Application.__init__(self)

def do_activate(self): win = MyWindow(self) win.show_all()

def do_startup(self): Gtk.Application.do_startup(self)

app = MyApplication() exit_status = app.run(sys.argv) sys.exit(exit_status)

# Nützliche Methoden für ein Scale-Widget

A Gtk.Adjustment is needed to construct the Gtk.Scale. This is the representation of a value with a lower and upper bound, together with step and page increments, and a page size, and it is constructed as `Gtk.Adjustment(value, lower, upper, step_increment, page_increment, page_size)` where the fields are of type `float`; `step_increment` is the increment/decrement that is obtained by using the cursor keys, `page_increment` the one that is obtained clicking on the scale itself. Note that `page_size` is not used in this case, it should be set to `0`.

In line 28 the signal `"value-changed"` is connected to the callback function `scale_moved()` using `widget.connect(signal, callback function)`. See for a more detailed explanation.

`get_value()` retrieves the current value of the scale; `set_value(value)` sets it (if the `value`, of type `float`, is outside the minimum or maximum range, it will be clamped to fit inside them). These are methods of the class Gtk.Range.

Use `set_draw_value(False)` to avoid displaying the current value as a string next to the slider.

To highlight the part of the scale between the origin and the current value:

self.h_scale.set_restrict_to_fill_level(False) self.h_scale.set_fill_level(self.h_scale.get_value()) self.h_scale.set_show_fill_level(True)

in the callback function of the "value-changed" signal, so to have the new filling every time the value is changed. These are methods of the class Gtk.Range.

`add_mark(value, position, markup)` adds a mark at the `value` (`float` or `int` if that is the precision of the scale), in `position` (`Gtk.PositionType.LEFT, Gtk.PositionType.RIGHT, Gtk.PositionType.TOP, Gtk.PositionType.BOTTOM`) with text `Null` or `markup` in the Pango Markup Language. To clear marks, `clear_marks()`.

`set_digits(digits)` sets the precision of the scale at `digits` digits.

# API-Referenzen

In diesem Beispiel haben wir Folgendes verwendet:

GtkScale

GtkAdjustment

Standard-Aufzählungen