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QGraphicsLinearLayout Class

The QGraphicsLinearLayout class provides a horizontal or vertical layout for managing widgets in Graphics View. More...

Header: #include <QGraphicsLinearLayout>
CMake: find_package(Qt6 REQUIRED COMPONENTS Widgets)
target_link_libraries(mytarget PRIVATE Qt6::Widgets)
qmake: QT += widgets
Inherits: QGraphicsLayout

Public Functions

QGraphicsLinearLayout(QGraphicsLayoutItem *parent = nullptr)
QGraphicsLinearLayout(Qt::Orientation orientation, QGraphicsLayoutItem *parent = nullptr)
virtual ~QGraphicsLinearLayout()
void addItem(QGraphicsLayoutItem *item)
void addStretch(int stretch = 1)
Qt::Alignment alignment(QGraphicsLayoutItem *item) const
void insertItem(int index, QGraphicsLayoutItem *item)
void insertStretch(int index, int stretch = 1)
qreal itemSpacing(int index) const
Qt::Orientation orientation() const
void removeItem(QGraphicsLayoutItem *item)
void setAlignment(QGraphicsLayoutItem *item, Qt::Alignment alignment)
void setItemSpacing(int index, qreal spacing)
void setOrientation(Qt::Orientation orientation)
void setSpacing(qreal spacing)
void setStretchFactor(QGraphicsLayoutItem *item, int stretch)
qreal spacing() const
int stretchFactor(QGraphicsLayoutItem *item) const

Reimplemented Public Functions

virtual int count() const override
virtual void invalidate() override
virtual QGraphicsLayoutItem *itemAt(int index) const override
virtual void removeAt(int index) override
virtual void setGeometry(const QRectF &rect) override
virtual QSizeF sizeHint(Qt::SizeHint which, const QSizeF &constraint = QSizeF()) const override

Detailed Description

The default orientation for a linear layout is Qt::Horizontal. You can choose a vertical orientation either by calling setOrientation(), or by passing Qt::Vertical to QGraphicsLinearLayout's constructor.

The most common way to use QGraphicsLinearLayout is to construct an object on the heap, passing a parent widget to the constructor, then add widgets and layouts by calling addItem().

QGraphicsScene scene;
QGraphicsWidget *textEdit = scene.addWidget(new QTextEdit);
QGraphicsWidget *pushButton = scene.addWidget(new QPushButton);

QGraphicsWidget *form = new QGraphicsWidget;
scene.addItem(form);

QGraphicsLinearLayout *layout = new QGraphicsLinearLayout(form);
layout->addItem(textEdit);
layout->addItem(pushButton);

Alternatively, if you do not pass a parent widget to the layout's constructor, you will need to call QGraphicsWidget::setLayout() to set this layout as the top-level layout for that widget, the widget will take ownership of the layout.

You can add widgets, layouts, stretches (addStretch(), insertStretch() or setStretchFactor()), and spacings (setItemSpacing()) to a linear layout. The layout takes ownership of the items. In some cases when the layout item also inherits from QGraphicsItem (such as QGraphicsWidget) there will be a ambiguity in ownership because the layout item belongs to two ownership hierarchies. See the documentation of QGraphicsLayoutItem::setOwnedByLayout() how to handle this. You can access each item in the layout by calling count() and itemAt(). Calling removeAt() or removeItem() will remove an item from the layout, without destroying it.

Size Hints and Size Policies in QGraphicsLinearLayout

QGraphicsLinearLayout respects each item's size hints and size policies, and when the layout contains more space than the items can fill, each item is arranged according to the layout's alignment for that item. You can set an alignment for each item by calling setAlignment(), and check the alignment for any item by calling alignment(). By default, items are aligned to the top left.

Spacing within QGraphicsLinearLayout

Between the items, the layout distributes some space. The actual amount of space depends on the managed widget's current style, but the common spacing is 4. You can also set your own spacing by calling setSpacing(), and get the current spacing value by calling spacing(). If you want to configure individual spacing for your items, you can call setItemSpacing().

Stretch Factor in QGraphicsLinearLayout

You can assign a stretch factor to each item to control how much space it will get compared to the other items. By default, two identical widgets arranged in a linear layout will have the same size, but if the first widget has a stretch factor of 1 and the second widget has a stretch factor of 2, the first widget will get 1/3 of the available space, and the second will get 2/3.

QGraphicsLinearLayout calculates the distribution of sizes by adding up the stretch factors of all items, and then dividing the available space accordingly. The default stretch factor is 0 for all items; a factor of 0 means the item does not have any defined stretch factor; effectively this is the same as setting the stretch factor to 1. The stretch factor only applies to the available space in the lengthwise direction of the layout (following its orientation). If you want to control both the item's horizontal and vertical stretch, you can use QGraphicsGridLayout instead.

QGraphicsLinearLayout Compared to Other Layouts

QGraphicsLinearLayout is very similar to QVBoxLayout and QHBoxLayout, but in contrast to these classes, it is used to manage QGraphicsWidget and QGraphicsLayout instead of QWidget and QLayout.

See also QGraphicsGridLayout and QGraphicsWidget.

Member Function Documentation

QGraphicsLinearLayout::QGraphicsLinearLayout(QGraphicsLayoutItem *parent = nullptr)

Constructs a QGraphicsLinearLayout instance using Qt::Horizontal orientation. parent is passed to QGraphicsLayout's constructor.

QGraphicsLinearLayout::QGraphicsLinearLayout(Qt::Orientation orientation, QGraphicsLayoutItem *parent = nullptr)

Constructs a QGraphicsLinearLayout instance. You can pass the orientation for the layout, either horizontal or vertical, and parent is passed to QGraphicsLayout's constructor.

[virtual] QGraphicsLinearLayout::~QGraphicsLinearLayout()

Destroys the QGraphicsLinearLayout object.

void QGraphicsLinearLayout::addItem(QGraphicsLayoutItem *item)

This convenience function is equivalent to calling insertItem(-1, item).

void QGraphicsLinearLayout::addStretch(int stretch = 1)

This convenience function is equivalent to calling insertStretch(-1, stretch).

Qt::Alignment QGraphicsLinearLayout::alignment(QGraphicsLayoutItem *item) const

Returns the alignment for item. The default alignment is Qt::AlignTop | Qt::AlignLeft.

The alignment decides how the item is positioned within its assigned space in the case where there's more space available in the layout than the widgets can occupy.

See also setAlignment().

[override virtual] int QGraphicsLinearLayout::count() const

Reimplements: QGraphicsLayout::count() const.

void QGraphicsLinearLayout::insertItem(int index, QGraphicsLayoutItem *item)

Inserts item into the layout at index, or before any item that is currently at index.

See also addItem(), itemAt(), insertStretch(), and setItemSpacing().

void QGraphicsLinearLayout::insertStretch(int index, int stretch = 1)

Inserts a stretch of stretch at index, or before any item that is currently at index.

See also addStretch(), setStretchFactor(), setItemSpacing(), and insertItem().

[override virtual] void QGraphicsLinearLayout::invalidate()

Reimplements: QGraphicsLayout::invalidate().

[override virtual] QGraphicsLayoutItem *QGraphicsLinearLayout::itemAt(int index) const

Reimplements: QGraphicsLayout::itemAt(int i) const.

When iterating from 0 and up, it will return the items in the visual arranged order.

qreal QGraphicsLinearLayout::itemSpacing(int index) const

Returns the spacing after item at index.

See also setItemSpacing().

Qt::Orientation QGraphicsLinearLayout::orientation() const

Returns the layout orientation.

See also setOrientation().

[override virtual] void QGraphicsLinearLayout::removeAt(int index)

Reimplements: QGraphicsLayout::removeAt(int index).

Removes the item at index without destroying it. Ownership of the item is transferred to the caller.

See also removeItem() and insertItem().

void QGraphicsLinearLayout::removeItem(QGraphicsLayoutItem *item)

Removes item from the layout without destroying it. Ownership of item is transferred to the caller.

See also removeAt() and insertItem().

void QGraphicsLinearLayout::setAlignment(QGraphicsLayoutItem *item, Qt::Alignment alignment)

Sets the alignment of item to alignment. If item's alignment changes, the layout is automatically invalidated.

See also alignment() and invalidate().

[override virtual] void QGraphicsLinearLayout::setGeometry(const QRectF &rect)

Reimplements: QGraphicsLayoutItem::setGeometry(const QRectF &rect).

void QGraphicsLinearLayout::setItemSpacing(int index, qreal spacing)

Sets the spacing after item at index to spacing.

See also itemSpacing().

void QGraphicsLinearLayout::setOrientation(Qt::Orientation orientation)

Change the layout orientation to orientation. Changing the layout orientation will automatically invalidate the layout.

See also orientation().

void QGraphicsLinearLayout::setSpacing(qreal spacing)

Sets the layout's spacing to spacing. Spacing refers to the vertical and horizontal distances between items.

See also spacing(), setItemSpacing(), setStretchFactor(), and QGraphicsGridLayout::setSpacing().

void QGraphicsLinearLayout::setStretchFactor(QGraphicsLayoutItem *item, int stretch)

Sets the stretch factor for item to stretch. If an item's stretch factor changes, this function will invalidate the layout.

Setting stretch to 0 removes the stretch factor from the item, and is effectively equivalent to setting stretch to 1.

See also stretchFactor().

[override virtual] QSizeF QGraphicsLinearLayout::sizeHint(Qt::SizeHint which, const QSizeF &constraint = QSizeF()) const

Reimplements: QGraphicsLayoutItem::sizeHint(Qt::SizeHint which, const QSizeF &constraint) const.

qreal QGraphicsLinearLayout::spacing() const

Returns the layout's spacing. Spacing refers to the vertical and horizontal distances between items.

See also setSpacing().

int QGraphicsLinearLayout::stretchFactor(QGraphicsLayoutItem *item) const

Returns the stretch factor for item. The default stretch factor is 0, meaning that the item has no assigned stretch factor.

See also setStretchFactor().

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