Getting the size of a QgsLayoutItem

Question

I am facing a problem with the Layout API while implementing a plugin for QGIS 3. I created a layout template , which contains different elements like map, labels, legend and scale-bar. I'd like to place my legend on the bottom of the page. But the size of the legend can change. So I wanted to place my legend using :

legend = QgsLayoutItemLegend(layout)
legend.setLinkedMap(map)
legend.setReferencePoint(QgsLayoutItem.LowerLeft)
legend.attemptMove(QgsLayoutPoint(page.pageSize().width()*0.79,page.pageSize().height()),useReferencePoint=True)

But this is not working and it gaves me the same result as without the setReferencePoint. So does anyone know why is the "LowerLeft" not working ?

A solution to my problem would be to get the height of my legend and place it from the default UpperLeft position, but I wasn't able to find out how to get that. Any idea on how to get the size of an item ?

Answer 1

Using an existing legend, I'm able to move the legend according to the reference point (try using the following code)

project = QgsProject.instance()
manager = project.layoutManager()
layout = manager.layoutByName('your_layout')
# Don't forget to select your legend
legend = layout.selectedLayoutItems()[0]

legend.setReferencePoint(QgsLayoutItem.LowerLeft)
print(legend.pagePositionWithUnits())
legend.attemptMove(QgsLayoutPoint(100, 200),useReferencePoint=True)
print(legend.pagePositionWithUnits())

legend.setReferencePoint(QgsLayoutItem.UpperRight)
print(legend.pagePositionWithUnits())
legend.attemptMove(QgsLayoutPoint(100, 200),useReferencePoint=True)
print(legend.pagePositionWithUnits())

Conclusion: you need to do add layout.addLayoutItem(legend) BEFORE running legend.attemptMove(... (or legend.attemptResize(...) as you need a reference point relative to the layout. It's not possible when the item has not been added to the layout.

No final conclusion at the moment as it's a refresh/timing issue e.g https://gist.github.com/ThomasG77/d15771bb30c231166701cf31788f8a6b#file-pyqgis-371225-py-L26

For the 2nd question within the first one e.g

Any idea on how to get the size of an item ?

Use

legend.sizeWithUnits()

Unfortunately, works when you run it standalone in the PyQGIS console not when using script in the above GIST.

Answer 2

to change reference point of an item in the layout. for your example, you need to replace

legend.setReferencePoint(QgsLayoutItem.LowerLeft)

with :

legend.setReferencePoint(6) # 6 is for the lowerLeft position 

you can change 6 with 0 to 8 with 0 for upperLeft(default reference point) / 4 : Middlecenter / 8 : LowerRight