backPressBehavior property
This decides the action to be taken when user presses the back button.
Note that this will continue to work, even if the panel is not currently visible. (i.e., PanelState.closed with height 0.0).
For normal panels, any of these can be used. But for Two-state panels, these behaviors can be used: BackPressBehavior.POP, BackPressBehavior.PERSIST, BackPressBehavior.CLOSE_POP.
Default : BackPressBehavior.POP
Implementation
final BackPressBehavior backPressBehavior;