scene() returning None?

[Oscar Branson]

Hello,

I'm attempting to implement an action based on sigMouseMoved, but have got seriously confused about how to access this signal.

The Project

I am creating multi-panel plots inside a larger pyqt application. To do this, I have contained everything within a  GraphicsView, which contains a central GraphicsLayout that contains the plots.

I am using PlotItem to create plots, which I then add to the GraphicsLayout using addItem.

This is all working fine, and I end up with two plots displayed - let's call them Plot1 and Plot2.

Now, I want to display the cursor position in a label, so I created a label and a mouseMoved function to update the label text.

The problem: I can't work out how to connect sigMouseMoved to my mouseMoved function.

Following the documentation and examples, I tried setting up a SignalProxy:

SignalProxy(Plot1.scene().sigMouseMoved, rateLimit=60, slot=mouseMoved)

When I try to run this, I get an AttributeError telling me that 'NoneType' object has no attribute 'sigMouseMoved'. I can't work out why calling scene() on my plots returns None!

The only difference I can see from the examples is that I'm manually creating 'PlotItem' rather than pyqtgraph.plot to create my plots... but as far as I can tell the .plot function is just a wrapper for creating a PlotItem.

Any help/pointers would be greatly appreciated... this is driving me mad!

Thanks,

Oscar.

[Patrick]

Hi,

I don't think the issue is just because you create the PlotItems separately. If I change the Crosshair/Mouse interaction example lines from

p1 = win.addPlot(row=1, col=0)
p2 = win.addPlot(row=2, col=0)

to

p1 = pg.PlotItem()
p2 = pg.PlotItem()
win.addItem(p1, row=1, col=0)
win.addItem(p2, row=2, col=0)

then the example still works fine.

I'm taking a guess and saying you're trying to connect the signal to the PlotItem before adding it to the GraphicsLayout. Until that happens, it doesn't know what GraphicsScene it's part of.

Patrick

[Oscar Branson]

Yep - that solved it. Was trying to make the connection before adding the plots. Doh! Thanks v much.