Mastering widget alignment and user interaction is crucial for any GUI application. This Python EFL tutorial explains how to use Weight Hints, Boxes, and Callbacks to create responsive layouts and interactive buttons. If you’re new to the series, start with our first window tutorial.
TL;DR: Layout & Interaction Summary
- Box Widget: A container used to pack multiple widgets (labels, buttons) together.
- Weight Hints: Tell EFL how to distribute space among widgets.
- Callbacks: Functions that trigger when a user interacts with a widget (e.g., clicking a button).
- Core Goal: Create a window with a label and a button that exits the app.
Understanding EFL Layout Logic
In Python EFL, widgets don’t just sit on the screen; they belong to containers. The most common container is the Box, which can arrange items horizontally or vertically.
What are Weight Hints?
Weight hints (size_hint_weight) are values ranging from 0.0 to 1.0. They define how much extra space a widget should take up. Using EVAS_HINT_EXPAND (which equals 1.0) ensures the widget expands to fill the available area.
Implementation Example: Labels and Buttons
This script demonstrates packing a Label and a Button into a Box, then connecting the button to an exit callback.
import efl.elementary as elm
from efl.elementary.box import Box
from efl.elementary.button import Button
from efl.elementary.label import Label
from efl.elementary.window import StandardWindow
from efl.evas import EVAS_HINT_EXPAND
# Expansion constant for cleaner code
EXPAND_BOTH = EVAS_HINT_EXPAND, EVAS_HINT_EXPAND
class MainWindow(StandardWindow):
def __init__(self):
StandardWindow.__init__(self, "ex2", "Interaction Demo", size=(300, 200))
self.callback_delete_request_add(lambda o: elm.exit())
# 1. Create a Label
our_label = Label(self)
our_label.size_hint_weight = EXPAND_BOTH
our_label.text = "Hello Elementary!"
our_label.show()
# 2. Create a Button with a Callback
our_button = Button(self)
our_button.size_hint_weight = EXPAND_BOTH
our_button.text = "Click to Exit"
our_button.callback_clicked_add(self.button_pressed)
our_button.show()
# 3. Create a Box container and pack widgets
our_box = Box(self)
our_box.size_hint_weight = EXPAND_BOTH
our_box.pack_end(our_label)
our_box.pack_end(our_button)
our_box.show()
# 4. Add the Box to the window
self.resize_object_add(our_box)
def button_pressed(self, btn):
# This function runs when the button is clicked
print("Exit button clicked!")
elm.exit()
if __name__ == "__main__":
elm.init()
gui = MainWindow()
gui.show()
elm.run()
Structured Data: Layout Options
| Component | Description | Usage |
|---|---|---|
| Box | Linear container | our_box.pack_end(widget) |
| Weight Hint | Expansion logic | widget.size_hint_weight = 1.0, 1.0 |
| Alignment | Positioning logic | widget.size_hint_align = 0.5, 0.5 |
| Callback | Event handling | widget.callback_clicked_add(func) |
Frequently Asked Questions (FAQ)
What is the difference between pack_start and pack_end?
pack_start adds the widget to the beginning of the list (top or left), while pack_end adds it to the end (bottom or right).
Why doesn’t my widget fill the whole window?
Make sure you have set the size_hint_weight to EXPAND_BOTH and added the widget (or its container) to the window using resize_object_add.
Can I nest Boxes inside Boxes?
Yes. You can pack a horizontal Box inside a vertical Box to create complex grid-like layouts without using a formal Grid widget.
Key Takeaways
- Use Boxes for simple linear layouts.
- Weight hints are essential for responsive resizing.
- Callbacks bridge the gap between the UI and your Python logic.
Written by
Abdur-Rahmaan Janhangeer
Chef
Python author of 9+ years having worked for Python companies around the world
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