gnome-weather is already single-instance (in the technical sense). Do you mean single window?
Because making g-w multi-window was a deliberate choice (it allows opening two cities at once, basically). Also, being single-window (as in: activate() calls present() on the current window) kinda breaks the ctrl+click and right-click-new-window in the shell.

(In reply to comment #1)
> gnome-weather is already single-instance (in the technical sense). Do you mean
> single window?
> Because making g-w multi-window was a deliberate choice (it allows opening two
> cities at once, basically).

I don't think it makes sense to have multi-window apps that use a content grid. The grid should be authoritative; and shouldn't be updating because changes have been made in another window.

If there's a real desire to be able to view the weather from more than one places at once, a better approach would be to bring more details into the overview grid.

*** Bug 740350 has been marked as a duplicate of this bug. ***

So, I am adding the ability to open Weather from Maps. I am using the ActivateAction DBus call to do so, with the Weather action 'show-location'. I was surprised that it open a new window for me. It wasn't what I expected.

Then again I am not all that familiar with Weather. Would it make sense to make the 'show-location' action do present on current window? It would affect Maps and the searchProvider?

What is the use-case for opening two cities at once? Should Weather perhaps behave more like Clocks and show two cities in the content if two cities are opened?

The show-location/multiple activation problem (which was an actual app bug) was solved in 3.16, and the design problem of the content grid was fixed.
I'm not changing the support for multiple windows any time soon, so closing.