How do you implement undo and redo? If “UNDO” string is encountered, pop the top element from Undo stack and push it to Redo stack. If “REDO” string is encountered, pop the top element of
How do you implement undo and redo?
If “UNDO” string is encountered, pop the top element from Undo stack and push it to Redo stack. If “REDO” string is encountered, pop the top element of Redo stack and push it into the Undo stack.
How can you use the Command pattern to implement undo and redo features?
When doing an undo, we take the top command from the undo stack and execute its undo() what restores the “original” state. The undone command is pushed to the redoStack(). When doing a redo, we take the top command from the redo stack and execute its redo() what restores the “new” state.
How do you undo a redo Command?
To undo an action, press Ctrl + Z. To redo an undone action, press Ctrl + Y.
How do you implement an undo system?
Undo
- Undo is an interaction technique which is implemented in many computer programs.
- In most Microsoft Windows applications, the keyboard shortcut for the undo command is Ctrl+Z or Alt+Backspace, and the shortcut for redo is Ctrl+Y or Ctrl+Shift+Z.
Which of these patterns can be used to implement undo/redo operations?
There are two main software development patterns that are the obvious choices when dealing with operations like undo and redo: Memento and Command patterns.
Which design pattern is useful to implement undo/redo actions?
The memento pattern is a software design pattern that provides the ability to restore an object to its previous state (undo via rollback). The memento pattern is implemented with three objects: the originator, a caretaker and a memento. The originator is some object that has an internal state.
What is undo Redo command?
The undo function is used to reverse a mistake, such as deleting the wrong word in a sentence. For example, if you typed a word, and then deleted it using an undo, the redo function restores the word you deleted (“undid”). Tip. On the PC, the shortcut key to redo is usually Ctrl + Y or Command + Y .
Why is Ctrl Y Redo?
Alternatively referred to as Control+Y and C-y, Ctrl+Y is a keyboard shortcut most often used to redo an action reversed using the undo command. For example, if you used the Ctrl+Z shortcut to undo what you thought was a mistake, but realize it wasn’t, you could press Ctrl+Y to redo the previous action.
How do you implement undo stack?
When user want to undo those operations, simply pop operations from the “performed” stack to a “recall” stack. When user wants to redo those operations, pop items from “recall” stack and push them back to “performed” stack. Hope it helps.
What do you need to implement undo/redo feature in an application?
To implement Undo , you work backward from the tail of the linked-list, using a ‘current-node’ pointer or index: where the change was insert , you do a delete but without updating the linked-list; and where it was a delete you insert the data from the data in the linked-list buffer.
Can you undo a design pattern?
What is difference between undo and Redo command?
The undo function is used to reverse a mistake, such as deleting the wrong word in a sentence. The redo function restores any actions that were previously undone using an undo. For example, if you typed a word, and then deleted it using an undo, the redo function restores the word you deleted (“undid”).
Which is simpler to implement, undo or redo?
+1 If the state of your objects are not very large, this is drastically simpler to implement than the undo/redo command pattern which can get complex very easily. And often times you will have destructive commands that cannot be undone without a full state copy anyway. But for very large states, this can be impractical.
How is the command pattern used in redo?
Using the command pattern, we can wrap a command as an object. We use the command history to support arbitrary-level undo and redo. The following simple description of command history is from the book, Design Patterns. Conceptually, the command history looks like the following graph, each circle represents a command object.
Which is the best pattern to use in undo?
There are two classic patterns to use. The first is the memento patternwhich is used to store snapshots of your complete object state. This is perhaps more system intensive than the command pattern, but it allows rollback very simply to an older snapshot.
What are the pros and cons of undo and redo?
An action creates a new state and a pointer is used to move between the states to allow for undo and redo. Pros Implementation is independent of the applied action. Once implemented we can add actions without worrying about breaking history. It is fast to advance to a predefined position in history.