The offset where RefreshProgressIndicator starts to appear on drag start.
Depending whether the indicator is showing on the top or bottom, the value of this variable controls how far from the parent's edge the progress indicator starts to appear. This may come in handy when, for example, the UI contains a top Widget which covers the parent's edge where the progress indicator would otherwise appear.
By default, the edge offset is set to 0.
- displacement, can be used to change the distance from the edge that the indicator settles.
final double edgeOffset;