QFormLayout Class

Detailed Description

QFormLayout is a convenience layout class that lays out its children in a two-column form. The left column consists of labels and the right column consists of "field" widgets (line editors, spin boxes, etc.).

Traditionally, such two-column form layouts were achieved using QGridLayout. QFormLayout is a higher-level alternative that provides the following advantages:

• Adherence to the different platform's look and feel guidelines.

  For example, the macOS Aqua and KDE guidelines specify that the labels should be right-aligned, whereas Windows and GNOME applications normally use left-alignment.

• Support for wrapping long rows.

  For devices with small displays, QFormLayout can be set to wrap long rows, or even to wrap all rows.

• Convenient API for creating label--field pairs.

  The addRow() overload that takes a QString and a QWidget * creates a QLabel behind the scenes and automatically set up its buddy. We can then write code like this:

   QFormLayout *formLayout = new QFormLayout;
   formLayout->addRow(tr("&Name:"), nameLineEdit);
   formLayout->addRow(tr("&Email:"), emailLineEdit);
   formLayout->addRow(tr("&Age:"), ageSpinBox);
   setLayout(formLayout);
  

  Compare this with the following code, written using QGridLayout:

   nameLabel = new QLabel(tr("&Name:"));
   nameLabel->setBuddy(nameLineEdit);
  
   emailLabel = new QLabel(tr("&Name:"));
   emailLabel->setBuddy(emailLineEdit);
  
   ageLabel = new QLabel(tr("&Name:"));
   ageLabel->setBuddy(ageSpinBox);
  
   QGridLayout *gridLayout = new QGridLayout;
   gridLayout->addWidget(nameLabel, 0, 0);
   gridLayout->addWidget(nameLineEdit, 0, 1);
   gridLayout->addWidget(emailLabel, 1, 0);
   gridLayout->addWidget(emailLineEdit, 1, 1);
   gridLayout->addWidget(ageLabel, 2, 0);
   gridLayout->addWidget(ageSpinBox, 2, 1);
   setLayout(gridLayout);
  

The table below shows the default appearance in different styles.

QCommonStyle derived styles (except QPlastiqueStyle)	QMacStyle	QPlastiqueStyle	Qt Extended styles
Traditional style used for Windows, GNOME, and earlier versions of KDE. Labels are left aligned, and expanding fields grow to fill the available space. (This normally corresponds to what we would get using a two-column QGridLayout.)	Style based on the macOS Aqua guidelines. Labels are right-aligned, the fields don't grow beyond their size hint, and the form is horizontally centered.	Recommended style for KDE applications. Similar to MacStyle, except that the form is left-aligned and all fields grow to fill the available space.	Default style for Qt Extended styles. Labels are right-aligned, expanding fields grow to fill the available space, and row wrapping is enabled for long lines.

The form styles can be also be overridden individually by calling setLabelAlignment(), setFormAlignment(), setFieldGrowthPolicy(), and setRowWrapPolicy(). For example, to simulate the form layout appearance of QMacStyle on all platforms, but with left-aligned labels, you could write:

 formLayout->setRowWrapPolicy(QFormLayout::DontWrapRows);
 formLayout->setFieldGrowthPolicy(QFormLayout::FieldsStayAtSizeHint);
 formLayout->setFormAlignment(Qt::AlignHCenter | Qt::AlignTop);
 formLayout->setLabelAlignment(Qt::AlignLeft);