primaryDelta property Null safety
final
The amount the pointer has moved along the primary axis in the coordinate space of the event receiver since the previous update.
If the GestureDragUpdateCallback is for a one-dimensional drag (e.g., a horizontal or vertical drag), then this value contains the component of delta along the primary axis (e.g., horizontal or vertical, respectively). Otherwise, if the GestureDragUpdateCallback is for a two-dimensional drag (e.g., a pan), then this value is null.
Defaults to null if not specified in the constructor.
Implementation
final double? primaryDelta;