Viewer buttons don't work as expected when having two napari viewers in a single program

🐛 Bug

Hi,

Since napari 0.4.8, the buttons that by default are in the lower left corner don’t work as expected when having two napari viewers in a single program. More specifically, when clicking one of the lower left corner buttons in the napari viewer that was added first, the button’s action is executed on the other viewer. This seems to be related to the new action manager features that were added in 0.4.8.

I’m not sure if this is actually a bug or if napari simply isn’t meant to be used like this, but until 0.4.8 I hadn’t experienced any issues, so it would be nice if it could continue to work when used like this.

To Reproduce

Steps to reproduce the behavior:

1. Run the following minimal working example with napari 0.4.8 or later:

import napari
from qtpy import QtWidgets
from skimage import data


class Window(QtWidgets.QWidget):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

        self.napari1 = napari.Viewer(show=False)
        self.napari1.add_image(data.cat())
        self.napari2 = napari.Viewer(show=False)
        self.napari2.add_image(data.astronaut())

        self.setLayout(QtWidgets.QHBoxLayout())
        self.layout().addWidget(self.napari1.window._qt_window)
        self.layout().addWidget(self.napari2.window._qt_window)


app = QtWidgets.QApplication([])
window = Window()
window.show()
app.exec_()

1. Click the console button in the lower left corner of the napari viewer that displays the cat image.

The console will show up in the napari viewer displaying the astronaut image, instead of in the one displaying the cat image.

The same issue applies to the other buttons in the lower left corner.

Environment

napari: 0.4.9
Platform: Windows-10-10.0.19041-SP0
Python: 3.9.4 (default, Apr 9 2021, 11:43:21) [MSC v.1916 64 bit (AMD64)]
Qt: 5.15.2
PyQt5: 5.15.4
NumPy: 1.19.3
SciPy: 1.6.3
Dask: 2021.05.0
VisPy: 0.6.6

OpenGL:
- GL version: 4.6.0 NVIDIA 465.89
- MAX_TEXTURE_SIZE: 32768

Screens:
- screen 1: resolution 2560x1440, scale 1.0

Plugins:
- console: 0.0.3
- scikit-image: 0.4.9
- svg: 0.1.5

Additional context

The keyboard shortcuts for the buttons work as expected.

[tlambert03]

I’m not sure if this is actually a bug or if napari simply isn’t meant to be used like this

definitely a bug! we still support multiple independent viewer instances. Thanks for the very clear report!

[brisvag]

git bisect says this started on #2612.