Add table-cell change callbacks

[tlambert03]

As pointed out by @pranathivemuri in https://github.com/napari/magicgui/pull/182#issuecomment-812670169 ... magicgui Table doesn't yet have a good way to bind a callback to a change event on a cell or a group of cells. (It was left for a later PR, and that time has come! 😄 )

https://github.com/napari/magicgui/blob/a07b6d3885fb63a6d7947fbb03fc90a971759006/magicgui/backends/_qtpy/widgets.py#L828-L832

[pranathivemuri]

Thanks so much for working on this! - Looking forward to this change.

[tlambert03]

@pranathivemuri, there is a workaround you can use in the meantime, by directly using the Qt api. Let's take the example at https://github.com/napari/magicgui/blob/master/examples/table.py ...

If, before running table.show(run=True) you added something like this, you can get a handle the cell change events:

def on_item_changed(item):
    # item will be an instance of `QTableWidgetItem`
    # https://doc.qt.io/Qt-5/qtablewidgetitem.html
    print('row:', item.row())
    print('col:', item.column())
    print('new data:', item.data(table._widget._DATA_ROLE))  # _DATA_ROLE will likely just be the number 255
    # whatever you want to do with the new value

table.native.itemChanged.connect(on_item_changed)

that might let you get started on some stuff until there is a "magicgui" way of doing it

[pranathivemuri]

awesome, I was just researching for this! in my case, it doesn't necessarily have to be a table it is just one text input from user that needs to be passed so there is probably multiple ways to work around it

[tlambert03]

oh! If it doesn't have to be a table... like if you just want to know if a user has changed a text input, then it's already supported (again, tables are a specific, special case)

see some docs here, but the basic idea is this:

# if using the decorator:

@magicgui
def func(your_name='Bob'):
    return f'hello {your_name}!'

# to connect to just the specific parameter changing
def _on_your_name_changed(event):
    print(f'your_name was changed to {event.value}')

func.your_name.changed.connect(_on_your_name_changed)


# to connect to the whole function being called
def _on_func_called(event):
    print(f"func called: {event.value}")

func.called.connect(_on_your_name_changed)

[pranathivemuri]

nice, thanks! I will just have to figure out passing this to current_properties in napari shapes layer to change the label for that bounding box. So far so good, thanks for all the example code! :)

[tlambert03]

feel free to point me to code if you need help

[pranathivemuri]

Thanks, it worked out. I will open-source the code in a few days, but it is working as I wanted. Thanks to the workaround you pointed out with QT table! I appreciate your quick replies today!