In my app, I needed to filter by state. So I have 50 checkboxes. I wasn't able to get the checkbox group to work, so I used the individual checkboxes.

Using individual checkboxes, I have a column widget that holds a checkbox widge and a text widget.
The text widget spells the name of the State. In this screenshot example the state is Alabama.
The checkbox widget is where the actions in the screenshot are taking place.

In the actions of the checkbox, there are two triggers that you have to fill out. The triggers are at the top and are named 'On Toggle On' and 'On Toggle Off'

The setup is to have created an app state that holds a list of stings. This list of string is basically where all of the selected (or Toggled On) States are held.
Once your app state is created, then you define your checkbox action to update that app state.
The Update Type: \"Add to List\"
The Value to add is the string of 'whatever you want'. In my case I wanted the U.S. state name (Alabama), to be added to the app state's list of strings. To do this you have to select the for a variable to be your \"Value to add.\"
Because the checkbox widget is just a check box, you have to say if this checkbox is cheched, then the string \"Alabama\" will be returned so The Variable will be a \"Conditional Value\"
The 'IF' will be another variable: \"Condition\"
Click the condition's \"First Value\" and under widget state, find the name of your checkbox widget. In the example my checkbox is named \"aLchekValue\"
Select \"Equal To\"
Second Value: \"True\" [ for the trigger Toggle Off, the Second Value will be \"False\"]
Press \"Confirm\"
The \"Then\" Value will be null or ?
Press \"Confirm\"

Copy and past the action to the 'On Toggle Off' trigger and make the Second Value: \"False\"

In my case, this uploaded any state that i selected and strings on the app state list were used to filter a list. but you can set a text field to display the app state also, and every string in the app state will be make up the letters for the text.

Get selected Items from CheckboxGroup