Making custom widget visible as layout element for printing in QGIS with PyQGIS

Question

I need to make a widget visible as a layout element for printing, for a QGIS plugin I am developing.

Which of the classes do I need to extend to do this?

After some research I think I begin to discern part of the procedure to achieve my goal:

• I have to implement or extend the QgsLayoutItem class.
• If I extend the QgsLayoutItem class, I must rewrite its draw() method in which I will define the way the widget will be drawn in the scene.
• However, QgsLayoutItem has many derived classes: QgsLayoutItemPage, QgsLayoutItemMap, QgsLayoutItemPicture, QgsLayoutItemLabel, QgsLayoutItemLegend, QgsLayoutItemShape, QgsLayoutItemFrame and others.

Answer 1

This is a partial answer which may not be exactly what you are looking for but perhaps a pointer to get you started. I think, in theory, the solution (or at least best avenue of research) is the QGraphicsProxyWidget class.

I made a few tests and achieved some, but not perfect results. The following code snippet adds a QWidget with child sub-widgets to a QgsPrintLayout object.

class TestProxyWidget(QGraphicsProxyWidget):
    def __init__(self):
        QGraphicsProxyWidget.__init__(self)
        self.w = CustomWidget()
        self.setWidget(self.w)
        
class CustomWidget(QWidget):
    def __init__(self):
        QWidget.__init__(self)
        self.layout = QHBoxLayout()
        self.lbl = QLabel('A Label:', self)
        self.le = QLineEdit(self)
        for w in self.children():
            self.layout.addWidget(w)
        self.setLayout(self.layout)
        
project = QgsProject.instance()
mgr = project.layoutManager()
layout = mgr.layoutByName('Test Layout')
proxy = TestProxyWidget()
layout.addItem(proxy)

The results are shown below, but as you can see- the size of the added widget is very large and I couldn't easily work out how to resize/scale the widget. Familiar methods like SetGeometry(), resize(), setMinimumSize(), setMaximumSize() etc don't work very well here. You can resize the parent widget, but the child widgets like labels, line edits, push buttons etc. don't scale properly. I'm sure there is a different approach to controlling the size but I'm not expert in this area as I haven't worked that much with Qt graphics classes and, unfortunately I don't much time at the moment to put into research.

If you do something like this example in the docs:

class CustomWidget(QWidget):
    def __init__(self):
        QWidget.__init__(self)
        self.layout = QHBoxLayout()
        self.lbl = QLabel('A Label:', self)
        self.cb = QComboBox(self)
        self.cb.addItems(['Large', 'Medium', 'Small'])
        self.pb = QPushButton('Click me', self)
        for w in self.children():
            self.layout.addWidget(w)
        self.setLayout(self.layout)

CW = CustomWidget()
scene = QGraphicsScene()
proxy = scene.addWidget(CW)
view = QGraphicsView(scene)
view.show()

The result looks like:

Perhaps this is more of a PyQt question (which might be better asked on Stack Overflow) or if you are lucky, a QGIS developer who knows a lot more about this than I do will give you a better answer here.