I want to make a tool where users can select one or more counties and easily see the calculated total area. So I added a Text Widget, turned on Connect To Data, found my Counties layer, and switched to the Selected Features View.
With the Text Widget selected, I clicked the stacked circles to make some Dynamic Content. In the Statistics Tab, I select the Sum Operator and the Field containing my area. Every polygon is required to have one, and by default, this usually looks like SHAPE.AREA().
I hit Insert and it works. The user can use the Select Widget or the Select Map Tool to pick some counties and instantly know their area. But, when they don't have anything selected, it looks like this...
