build method
override
Declares this node's children and behavior.
Runs once on mount, and again on every rebuild.
super.build() is required, as skipping it drops whatever the superclass
declared.
Implementation
@override
void build() {
super.build();
final recognizer = _recognizer = ImmediateMultiDragGestureRecognizer()..onStart = _handleStart;
trash(() {
_drag?.cancel();
recognizer.dispose();
_recognizer = null;
});
}