PyQt - QGraphicsAnchorLayout

In GUI building, an Anchor layout is a layout manager that allows user to position and size widget relative to the edge of a container. It is useful when we want to maintain the position of widget regardless of the overall window size. The widget can be anchored to top, left, right, bottom, and center of the container.

In PyQt, a class QGraphicsAnchorLayout provides a layout where one can anchor widgets together in Graphics View.

The anchor layout enables developers to specify the positioning of widgets concerning the layout and each other. Anchors are added to the layout using addAnchor(), addAnchors(), or addCornerAnchors().

Use the anchor() function to access existing anchors in the layout. Anchored items will be automatically added and removed from the layout as needed.

Anchors are always established between the edges of an object, including the "center" as an edge.

Below the given example −

layout.addAnchor(b, Qt.AnchorLeft, a, Qt.AnchorRight)
layout.addAnchor(b, Qt.AnchorTop, a, Qt.AnchorBottom)

In the above arrangement, the right edge of item a is attached to the left edge of item b while the bottom edge of item a is attached to the top edge of item b. This results in item b being positioned diagonally to the right and below item a.

Anchor are used to match the widget or height of the width. Thus, this is convenient to use the addAnchor() function.

Example

Following example illustrate the code snippet of QGraphicsAnchorLayout to build the group of containers or boxes.

import sys
from PyQt5.QtCore import QSizeF, Qt
from PyQt5.QtWidgets import (QApplication, QGraphicsAnchorLayout,
QGraphicsProxyWidget, QGraphicsScene, QGraphicsView, QGraphicsWidget,
QPushButton, QSizePolicy)
def createItem(minimum, preferred, maximum, name):
   wid = QGraphicsProxyWidget()

   wid.setWidget(QPushButton(name))
   wid.setMinimumSize(minimum)
   wid.setPreferredSize(preferred)
   wid.setMaximumSize(maximum)
   wid.setSizePolicy(QSizePolicy.Preferred, QSizePolicy.Preferred)

   return wid
if __name__ == '__main__':

   app = QApplication(sys.argv)

   scene = QGraphicsScene()
   scene.setSceneRect(0, 0, 800, 480)

   minSize = QSizeF(30, 100)
   prefSize = QSizeF(210, 100)
   maxSize = QSizeF(300, 100)

   a = createItem(minSize, prefSize, maxSize, "BOX 1")
   b = createItem(minSize, prefSize, maxSize, "BOX 2")
   c = createItem(minSize, prefSize, maxSize, "BOX 3")
   d = createItem(minSize, prefSize, maxSize, "BOX 4")
   e = createItem(minSize, prefSize, maxSize, "BOX 5")
   f = createItem(QSizeF(30, 50), QSizeF(150, 50), maxSize, "BOX 6")
   g = createItem(QSizeF(30, 50), QSizeF(30, 100), maxSize, "BOX 7")

   lay = QGraphicsAnchorLayout()
   lay.setSpacing(0)

   wid2 = QGraphicsWidget(None, Qt.Window)
   wid2.setPos(20, 20)
   wid2.setLayout(lay)

   # Vertical
   lay.addAnchor(a, Qt.AnchorTop, lay, Qt.AnchorTop)
   lay.addAnchor(b, Qt.AnchorTop, lay, Qt.AnchorTop)

   lay.addAnchor(c, Qt.AnchorTop, a, Qt.AnchorBottom)
   lay.addAnchor(c, Qt.AnchorTop, b, Qt.AnchorBottom)
   lay.addAnchor(c, Qt.AnchorBottom, d, Qt.AnchorTop)
   lay.addAnchor(c, Qt.AnchorBottom, e, Qt.AnchorTop)

   lay.addAnchor(d, Qt.AnchorBottom, lay, Qt.AnchorBottom)
   lay.addAnchor(e, Qt.AnchorBottom, lay, Qt.AnchorBottom)

   lay.addAnchor(c, Qt.AnchorTop, f, Qt.AnchorTop)
   lay.addAnchor(c, Qt.AnchorVerticalCenter, f, Qt.AnchorBottom)
   lay.addAnchor(f, Qt.AnchorBottom, g, Qt.AnchorTop)
   lay.addAnchor(c, Qt.AnchorBottom, g, Qt.AnchorBottom)

   # Horizontal
   lay.addAnchor(lay, Qt.AnchorLeft, a, Qt.AnchorLeft)
   lay.addAnchor(lay, Qt.AnchorLeft, d, Qt.AnchorLeft)
   lay.addAnchor(a, Qt.AnchorRight, b, Qt.AnchorLeft)

   lay.addAnchor(a, Qt.AnchorRight, c, Qt.AnchorLeft)
   lay.addAnchor(c, Qt.AnchorRight, e, Qt.AnchorLeft)

   lay.addAnchor(b, Qt.AnchorRight, lay, Qt.AnchorRight)
   lay.addAnchor(e, Qt.AnchorRight, lay, Qt.AnchorRight)
   lay.addAnchor(d, Qt.AnchorRight, e, Qt.AnchorLeft)

   lay.addAnchor(lay, Qt.AnchorLeft, f, Qt.AnchorLeft)
   lay.addAnchor(lay, Qt.AnchorLeft, g, Qt.AnchorLeft)
   lay.addAnchor(f, Qt.AnchorRight, g, Qt.AnchorRight)

   scene.addItem(wid2)
   scene.setBackgroundBrush(Qt.lightGray)

   view = QGraphicsView(scene)
   view.show()
   sys.exit(app.exec_())

Output

The above code produces the following output −