Aligning Buttons in Qt Dialogs: Alternatives to QDialogButtonBox::centerButtons

Purpose

• When set to false, the buttons are left-aligned within the box.
• When set to true (default), the buttons are centered horizontally.
• In a QDialogButtonBox widget, it controls the horizontal alignment of the buttons within the box.

Usage

1. #include <QtWidgets>
   

2. Create a QDialogButtonBox object
   

   QDialogButtonBox buttonBox(Qt::Horizontal); // Create a horizontal button box
   

3. Set the button alignment
   

   • To center the buttons:

     buttonBox.setCenterButtons(true);
     

   • To left-align the buttons:

     buttonBox.setCenterButtons(false);
     

4. Use the button box
   

   • You can typically add the QDialogButtonBox to a layout in your dialog or window to display the buttons.
   • Connect to the accepted and rejected signals (if using standard buttons) to handle user interaction.

Key Points

• Left-alignment can be useful for specific design choices or layouts where you want more control over button placement.
• Centering the buttons creates a visually balanced layout, especially when dealing with buttons of varying widths.
• QDialogButtonBox is commonly used in dialogs and windows to provide standard buttons like "OK," "Cancel," "Apply," etc.

Example

#include <QtWidgets>

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    QDialogButtonBox buttonBox(Qt::Horizontal);
    buttonBox.setCenterButtons(true);

    QPushButton* okButton = buttonBox.addButton(QDialogButtonBox::Ok);
    QPushButton* cancelButton = buttonBox.addButton(QDialogButtonBox::Cancel);

    // Connect to signals (if needed)
    QObject::connect(okButton, &QPushButton::clicked, [&]() {
        // Handle OK button click
    });

    QObject::connect(cancelButton, &QPushButton::clicked, [&]() {
        // Handle Cancel button click
    });

    buttonBox.show();

    return app.exec();
}

---

Standard Buttons with Vertical Layout

#include <QtWidgets>

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    QDialogButtonBox buttonBox(Qt::Vertical);
    buttonBox.setCenterButtons(true);  // Center buttons even in a vertical layout

    QPushButton* okButton = buttonBox.addButton(QDialogButtonBox::Ok);
    QPushButton* cancelButton = buttonBox.addButton(QDialogButtonBox::Cancel);
    QPushButton* applyButton = buttonBox.addButton(QDialogButtonBox::Apply);

    buttonBox.show();

    return app.exec();
}

This code creates a vertical QDialogButtonBox with three standard buttons ("OK," "Cancel," and "Apply") that are centered horizontally.

Custom Buttons with Grid Layout

#include <QtWidgets>

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    QWidget window;
    QGridLayout* layout = new QGridLayout(&window);

    QLabel* label = new QLabel("Are you sure?");
    layout->addWidget(label, 0, 0, 1, 2);

    QDialogButtonBox buttonBox(Qt::Horizontal);
    buttonBox.setCenterButtons(false);  // Left-align buttons

    QPushButton* yesButton = new QPushButton("Yes");
    QPushButton* noButton = new QPushButton("No");
    buttonBox.addButton(yesButton, QDialogButtonBox::ActionRole);
    buttonBox.addButton(noButton, QDialogButtonBox::RejectRole);

    layout->addWidget(&buttonBox, 1, 0, 1, 2);

    window.setLayout(layout);
    window.show();

    return app.exec();
}

Advanced: Button Roles and Signals

#include <QtWidgets>

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);

    QDialogButtonBox buttonBox(Qt::Horizontal);
    buttonBox.setCenterButtons(true);

    QPushButton* saveButton = buttonBox.addButton(QDialogButtonBox::Save);
    QPushButton* discardButton = buttonBox.addButton(QDialogButtonBox::Discard);

    QObject::connect(saveButton, &QPushButton::clicked, [&]() {
        // Handle Save button click (e.g., save data)
    });

    QObject::connect(discardButton, &QPushButton::clicked, [&]() {
        // Handle Discard button click (e.g., prompt confirmation)
    });

    int result = buttonBox.exec(); // Show the button box modally and get the result

    if (result == QDialogButtonBox::Save) {
        // User clicked Save button
    } else if (result == QDialogButtonBox::Discard) {
        // User clicked Discard button
    }

    return app.exec();
}

This code demonstrates using custom button roles (provided by QDialogButtonBox::Save and QDialogButtonBox::Discard) and connecting to their clicked signals for handling user actions. It also shows using buttonBox.exec() to display the box modally and retrieve the clicked button's result.

---

1. • You can create a layout manager (e.g., QHBoxLayout, QGridLayout) and add your buttons to it.
   • Set the layout's alignment property to Qt::AlignHCenter to center the buttons horizontally within the available space.

   QHBoxLayout* layout = new QHBoxLayout;
   QPushButton* button1 = new QPushButton("Button 1");
   QPushButton* button2 = new QPushButton("Button 2");
   layout->addWidget(button1);
   layout->addWidget(button2);
   layout->setAlignment(Qt::AlignHCenter);
   // Add the layout to your widget (e.g., dialog)
   

2. Using QSpacerItem
   

   • Create a QHBoxLayout and add your buttons.
   • Insert a QSpacerItem with appropriate stretching factors between the buttons to achieve centering.

   QHBoxLayout* layout = new QHBoxLayout;
   QPushButton* button1 = new QPushButton("Button 1");
   QPushButton* button2 = newPushButton("Button 2");
   layout->addWidget(button1);
   layout->addItem(new QSpacerItem(40, 0, QSpacerItem::Expanding)); // Adjust spacing as needed
   layout->addWidget(button2);
   // Add the layout to your widget
   

3. CSS Stylesheets (Qt Style Sheets)
   

   • If you're using Qt Style Sheets, you can define a custom style for your buttons that includes a justify-content: center property to achieve horizontal centering within their container.

   QPushButton {
       justify-content: center;
   }
   

Choosing the Right Approach

• If you're using Qt Style Sheets extensively, applying styles offers a centralized way to style your buttons consistently.
• For more complex layouts with spacers or specific spacing requirements, the QSpacerItem approach provides more control.
• For simple button layouts, using a QHBoxLayout with alignment is straightforward.