# CSE 340 Lab 7 (Spring 2019) ## Undo --- ## 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: Activity Files - `MainActivity` inherits from `ReversibleDrawingActivity`, which inherits from `DrawingActivity` - `DrawingActivity` - abstract class for app that supports drawing without history - Wrapper around a `DrawingView` - `doAction()` - `ReversibleDrawingActivity` - abstract class that extends DrawingActivity - adds support for undo/redo - includes buttons for undo/redo - `doAction()`, `undo()`, `redo()` - `MainActivity` - inherits from `ReversibleDrawingActivity` - adds support for thickness, color actions - `onColorSelected()`, `onThicknessSelected()` --- ## Codebase: DrawingView, Code Structure, and Layouts - `DrawingActivity` is a wrapper around a `DrawingView` - Sets behavior for how strokes are drawn -- Strokes are just `StrokeView`'s in the `DrawingView` - `onTouchEvent()` implements a PPS that describes lifetime of a stroke being created - Useful diagram on the spec makes the code structure clear - Also look at the layout files - you'll probably need to use them --- ## Codebase: Actions - `Action` abstract class defines basic behavior any Action should have - `ReversibleAction` abstract class defines interface for actions that can be undone - `DrawingActivity`'s `doAction()` calls `Action`'s `doAction()` to apply an action - `ReversibleDrawingActivity`'s `undo()` and `redo()` call methods on ReversibleAction to undo/redo - The three actions: - `ChangeColorAction` - `ChangeThicknessAction` - `StrokeAction` --- ## Codebase: History - The `ReversibleDrawingActivity` uses an AbstractHistory 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? --- ## Additional Responsibilities - Add a new thickness button with stroke width 0 - Add a new feature - Can be a new FAB (cannot add another thickness, but could add another color) - Challenges: -- Leverage your ColorPicker -- Allow the user to move a stroke - Improve usability (optional) - Make sure all added features are accessible --- ## Demo: Adding a new color FAB - This is very similar to adding a new thickness - `color_menu.xml` is the layout file with all the color FABs - Create a new FAB -- can just copy and paste, changing relevant attributes - Update MainActivity.java -- It already adds the other thickness and color FABs -- `addCollapsableMenu()` adds all buttons in an array to a menu and sets their listeners for you -- All you have to do is update the appropriate listener function (in this case, `onColorSelected()`)
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