fling method
void
fling()
Toggles the backdrop functionality.
If the back layer was concealed, it is animated to the "revealed" state by this function. If it was revealed, this function will animate it to the "concealed" state.
Implementation
void fling() {
FocusScope.of(context).unfocus();
if (isBackLayerConcealed) {
revealBackLayer();
} else {
concealBackLayer();
}
}