# CSE 340 Week 9 (Winter 2020) ## Undo Assignment --- ## Agenda - Understanding Undo Assignment - Practice Undo Exam Question - Review Lecture Slides / General Questions --- ## The Undo feature - Incredibly useful interaction technique - Reverts the application to an older state - Mistakes can easily be undone - *"Ugh...that was definitely not right, but manually erasing all this work is going to take forever"* --- ## The Redo feature - Inverse to the Undo feature - "Undoes" an undo - Work previously undone is reapplied - *"Huh, maybe I made the right decision after all..."* --- ## Codebase: Application - `ReversibleDrawingActivity`, class contains the entire interactor hierarchy - Floating Action Buttons (FAB), buttons that allow for actions supported by AbstractReversibleDrawingActivity - References DrawingView in AbstractDrawingActivity - `AbstractReversibleDrawingActivity`, abstract class that extends AbstractDrawingActivity - adds support for undo/redo - includes buttons for undo/redo - `doAction()`, `undo()`, `redo()` --- ## Codebase: Application - `AbstractDrawingActivity` - abstract class for app that supports drawing without history - Wrapper around a `DrawingView` - `doAction()` - contains methods for adding menus and changing visibility --- ## Codebase: DrawingView - `AbstractDrawingActivity` is a wrapper around a `DrawingView` - Sets behavior for how strokes are drawn - DrawingView, a drawing canvas that handles strokes - Strokes are just `StrokeView`'s in the `DrawingView` - `onTouchEvent()` implements a PPS that describes lifetime of a stroke being created --- ## Codebase: Actions - `AbstractAction` abstract class defines basic behavior any Action should have - `AbstractReversibleAction` abstract class defines interface for actions that can be undone - doAction() chain AbstractReversibleDrawingActivity.doAction()->AbstractDrawingActivity.doAction()->AbstractAction.doAction() - `AbstractReversibleDrawingActivity`'s `undo()` and `redo()` call methods on ReversibleAction to undo/redo - Actions: - `ChangeColorAction` - `ChangeThicknessAction`, implement for homework - `StrokeAction` - (more!), create your own action! --- ## Codebase: History - The `AbstractReversibleDrawingActivity` uses an StackHistory interface to manage the undo/redo history - You will implement the concrete StackHistory which implements AbstractHistory - Think: What data structures are used? Why does this make sense? -- What happens to the redo history if you take a new action after undoing a couple times? -- What happens to the undo history if you redo an action? -- What happens to the redo history if you undo an action? --- End
