Resizing Strategies for Custom QAbstractSpinBox Subclasses in Qt

• Custom Logic (Use with Caution)
  While drawing is discouraged, subclasses could implement specific logic based on the new size in resizeEvent(). This should be done cautiously, as frequent resizing can lead to performance issues.

• Layout Adjustment
  When the spin box is resized, its child widgets, like the line edit for entering the value, might need to be resized or repositioned to fit the new dimensions. Subclasses of QAbstractSpinBox can potentially use resizeEvent() to handle this layout adjustment.

Key Points

• Avoid using it for drawing operations.
• Subclasses can override it to handle layout adjustments or specific resizing logic.
• QAbstractSpinBox itself doesn't provide a specific implementation for resizeEvent().

---

#include <QtWidgets>

class MySpinBox : public QAbstractSpinBox {
  Q_OBJECT

public:
  MySpinBox(QWidget* parent = nullptr) : QAbstractSpinBox(parent) {}

protected:
  void resizeEvent(QResizeEvent* event) override {
    QAbstractSpinBox::resizeEvent(event); // Call base class implementation

    // Access the line edit widget
    QLineEdit* lineEdit = this->lineEdit();
    if (lineEdit) {
      // Adjust the size and position of the line edit based on new dimensions
      int margin = 5; // Adjust margin as needed
      lineEdit->setGeometry(margin, margin, width() - 2 * margin, height() - 2 * margin);
    }
  }
};

In this example:

1. We create a subclass MySpinBox inheriting from QAbstractSpinBox.
2. The resizeEvent() function overrides the base class implementation.
3. First, it calls the base class resizeEvent() using QAbstractSpinBox::resizeEvent(event). This ensures any base class resizing logic is executed.
4. Then, it retrieves the QLineEdit widget using lineEdit().
5. Finally, it adjusts the geometry of the line edit to fit within the new dimensions of the spin box, considering a margin.

---

1. • The preferred approach is to use layout managers like QHBoxLayout or QVBoxLayout to arrange child widgets within your spin box subclass. These layouts automatically handle resizing and positioning of widgets based on the available space.

2. QWidget::setContentsMargins
   

   • Use setContentsMargins on the spin box itself to define margins between the edge of the spin box and its child widgets. This ensures consistent spacing regardless of the spin box size.

3. QWidget::minimumSizeHint and QWidget::maximumSizeHint
   

   • Override these functions in your spin box subclass to specify the minimum and maximum sizes it can accommodate. This helps prevent the spin box from becoming too small or too large, ensuring proper layout of child widgets.

4. Signals and Slots
   

   • In some cases, you might want to react to the spin box being resized in another part of your application. Here, you can connect the geometryChanged signal of the spin box to a custom slot that performs any necessary layout adjustments.

Choosing the Right Approach

• Consider signals and slots for specific scenarios where resizing needs to trigger actions outside the spin box itself.
• Override minimumSizeHint and maximumSizeHint if you have specific size constraints for your spin box.
• Use setContentsMargins to define consistent spacing between the spin box edge and its children.
• For most cases, using layout managers (QHBoxLayout or QVBoxLayout) is the recommended approach for managing layout within your spin box subclass. It provides a flexible and efficient way to handle resizing and positioning of child widgets.