What We Know About QComboBox

Table of Contents

• Introduction
• Interactions
• Important Methods
• Signals and Event Handling
• Inspection and Debugging
• Summary

Introduction

A QComboBox is a drop-down list box (also known as a combo box or DDL) used in GUI applications to let the user select one item from a list. Combo boxes may also support editing, allowing users to type in values that are not in the list.

This tab demonstrates and documents the use of the QComboBox widget in a PyQt5 application. Two combo boxes are used and controlled by several methods that mutate their appearance and behavior.

The key points:

• When clicked, combo boxes expand to show their entire list of values.
• When one item on the list is clicked, combo boxes shrink to show only the one selected value.
• They can be editable, meaning the user can type new values.
• They emit signals when the user changes selection or enters text.
• They can be modified at runtime, with items added, removed, or reloaded.

Like other tabs in this application, this is a reference tab, showing expected widget behavior and tab structure.

📄 Code file:
qt5_by_example/tabs/basic_widgets/tab_q_combo_box.py
💡 View it in your IDE for full effect.

The documentation includes detailed comments in _build_gui_widgets() and the various mutate_ methods. This is part of the tab documentation pattern used throughout the project. See also: Tab Framework Code.

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Interactions

Try the following actions on this tab:

• Use the dropdown in combo_1 to select values from a predefined list.
• In combo_2, type a custom value and press Enter.
• Press the "combo\n_reload" button to clear and reload combo_1.
• Use the mutate button to explore different programmatic changes to the combo boxes.
• Observe the signal messages logged in the text area below the widgets.
• Use Inspect to examine internal state.

What You Can Observe

• combo_1 is a static dropdown list.
• combo_2 is editable, supporting typed input.
• Text changes and index changes trigger signal handlers.
• Mutate methods alter content, selection, or visibility.
• You can inspect widget properties via mutate_3() and inspect().

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Important Methods

_build_gui_widgets(self, main_layout)

Initializes two combo boxes:

• combo_1 is filled with static items and starts with "Two" selected.
• combo_2 is editable and also preloaded with values.
• Both combo boxes are connected to currentIndexChanged and currentTextChanged handlers.
• Adds a reload button and other standard controls.

mutate_0()

• Modifies combo_2 using .lineEdit().setText().
• Logs the current text of combo_1.

mutate_1() and mutate_2()

• Sets values for `combo