Visual design can be done quickly while keeping code clean and extensible. You’ll learn the secret of separating interface from logic so that form changes don’t break architecture and save hours on each iteration step.
We’ll cover 4 ways to integrate ui-forms (from direct to dynamic loading via QUiLoader), plus working with Property Editor, layouts, tab order, and quick signals/slots binding in F4 mode.
If this tool is already in your arsenal — you’ll stop “drawing UI in code” where it’s not needed. If not — there’s a risk of continuing yesterday’s work with yesterday’s tools.
This chapter includes ready-to-use code examples.
Chapter Self-Check
Why is it impossible to implement additional logic, such as a slot for a Reset button, when using the direct approach?Answer
Correct answer: Because the form is created via setupUi() directly without creating your own class, and there’s no place to add custom methods and slots.
What’s the main advantage of multiple inheritance over regular inheritance when working with forms?Answer
Correct answer: The ability to access form widgets directly (e.g., m_sld) instead of using the m_ui prefix (m_ui.m_sld), which simplifies code.
Why use Spacer (space filler) when creating layouts?Answer
Correct answer: To preserve free space between widgets and ensure correct scaling when window size changes, preventing widgets from stretching across the entire available area.
Why must you explicitly check the returned pointer for null when using QUiLoader?Answer
Correct answer: The load() method will return a null pointer on errors in the ui-file’s XML data, and using an invalid pointer will crash the application.
What happens if you don’t specify the ui-file in the FORMS section of a qmake project or don’t add it to the CMake source list?Answer
Correct answer: The build system won’t automatically create the ui_*.h header file from the ui-file, making it impossible to use the form in code.
What’s the difference between Edit Widgets and Edit Signals/Slots modes in Qt Designer?Answer
Correct answer: Edit Widgets is for adding widgets and changing their properties, while Edit Signals/Slots is for visually connecting widget signals to slots of other widgets.
Why is it important to set widget names in the objectName field in Qt Designer?Answer
Correct answer: These names become class attribute names in generated code, through which widgets are accessed for connecting to signals/slots and managing them.
What’s the practical benefit of using layouts instead of fixed widget positioning?Answer
Correct answer: Layouts automatically recalculate widget sizes and positions when window size changes, ensuring interface adaptability and correct display across different screen resolutions.
How does the Promote to… function solve the problem of using custom widgets in Qt Designer?Answer
Correct answer: It replaces a standard widget (e.g., QWidget) with a custom class in generated code, including the corresponding header file without needing to integrate the widget into Qt Designer.
Why doesn’t dynamic form loading via QUiLoader require including the ui-file in the FORMS section?Answer
Correct answer: Because the ui-file is used as a resource directly at runtime, and QUiLoader interprets XML on the fly, creating widgets without pre-generating a header file.
Why set the “Show signals and slots inherited from QWidget” checkbox when connecting a Quit button to the close() slot?Answer
Correct answer: The close() slot doesn’t belong directly to the form but is inherited from the QWidget base class, so without this checkbox it doesn’t appear in the available slots list.
In which scenario does it make sense to choose dynamic form loading over the three static approaches?Answer
Correct answer: When you need the ability to change the interface without recompiling the application, for example, to load different form versions or create user-editable interfaces.
Why is the findChild<Type*>(“ObjectName”) method critically important with dynamic form loading?Answer
Correct answer: With dynamic loading, there’s no direct access to widgets via class attributes, and findChild() is the only way to get widget pointers by their names for further work.
Practical Assignments
Easy Level
Calculator with Operation History
Create a calculator form in Qt Designer with two input fields (QLineEdit), four operation buttons (+, -, *, /), and a label (QLabel) to display the result. Implement the application using the inheritance approach, where each button is connected to a slot performing the corresponding operation.
Hints: Use vertical layout for input fields, horizontal for operation buttons. Apply text() and setText() methods to work with text. Convert strings to numbers via toDouble(). In the class, implement calculate() slots for each operation.
Medium Level
Settings Editor with Validation
Create an application settings form using multiple inheritance. The form should contain: username input field, age spinner (QSpinBox), language selection combo box (QComboBox), “Remember settings” checkbox, and two buttons “Apply” and “Cancel”. Use the Promote to… function to integrate a custom email validation widget. Implement data correctness checking before applying.
Hints: Create an EmailValidator class inherited from QLineEdit with an isValid() method. In Qt Designer, place QLineEdit and apply Promote to EmailValidator. Use setRange() for QSpinBox (18-100). The “Apply” button should be active only with valid data. Connect textChanged() and valueChanged() signals to a validation slot.
Hard Level
Dynamic UI Plugin Loading System
Develop an application that dynamically loads various ui-forms from resources or filesystem via QUiLoader. Create a main window with QListWidget displaying available plugin forms. When selecting a list item, the corresponding form should load and display in QStackedWidget. Implement automatic discovery of all widgets in the loaded form and output their list in QTreeWidget with hierarchy. Add ability to dynamically connect form widget signals with a universal logger slot.
Hints: Store ui-files in resources (qrc) or read from directory. Use QUiLoader::load() to create widgets. The findChildren() method will help find all child widgets recursively. Use QObject::parent() for hierarchy. Implement dynamic signal connection via QMetaObject::connectSlotsByName() or manually through connect() with QMetaMethod. Don’t forget to handle ui-file loading errors.
💬 Join the Discussion!
Mastered Qt Designer and ways to integrate forms into projects? Which approach seemed most convenient to you — multiple inheritance or dynamic loading?
Perhaps you have questions about when to use QUiLoader versus compiling forms statically? Or you found interesting applications for the Promote to… function for your widgets?
Share your experience, ask questions, or help other readers figure out the practical assignments!