Class UndoStack

An undo stack maintains a stack of commands that have been applied in your application.

New commands are pushed on the stack using Push(UndoCommand). Commands can be undone and redone using Undo() and Redo().

UndoStack keeps track of the current command. This is the command which will be executed by the next call to Redo(). The index of this command is returned by index. The state of the edited object can be rolled forward or back using index. If the top-most command on the stack has already been redone, index is equal to count.

UndoStack provides *command compression*, command *macros*, and supports the concept of a *clean state*.

Inheritance
object
UndoStack
Inherited Members
Namespace: Unity.AppUI.Undo
Assembly: Unity.AppUI.Undo.dll
Syntax
public class UndoStack

Constructors

UndoStack()

Default constructor.

Declaration
public UndoStack()

Properties

this[int]

Gets the command at the given index.

Declaration
public UndoCommand this[int idx] { get; }
Parameters
Type Name Description
int idx

The index of the command.
Property Value
Type Description
UndoCommand

The command at the given index, or null if the index is out of range.

canRedo

Weather the redo stack is empty.

Declaration
public bool canRedo { get; }
Property Value
Type Description
bool

canUndo

Weather the undo stack is empty.

Declaration
public bool canUndo { get; }
Property Value
Type Description
bool

cleanIndex

The index of the clean state. -1 if there is no clean state.

Declaration
public int cleanIndex { get; }
Property Value
Type Description
int

commands

The whole commands list.

Declaration
public IEnumerable<UndoCommand> commands { get; }
Property Value
Type Description
IEnumerable<UndoCommand>

count

The number of commands in the stack. Macros are counted as a single command.

Declaration
public int count { get; }
Property Value
Type Description
int

index

The index of the last command in the undo stack.

Declaration
public int index { get; set; }
Property Value
Type Description
int

isClean

Weather the undo stack is in a clean state. The clean state is useful when the application supports saving and restoring the state of an object.

Declaration
public bool isClean { get; }
Property Value
Type Description
bool

lastCommand

The last command in the undo stack.

Declaration
public UndoCommand lastCommand { get; }
Property Value
Type Description
UndoCommand

memorySize

The total memory size of the undo stack.

Declaration
public ulong memorySize { get; }
Property Value
Type Description
ulong

undoLimit

The maximum number of memory units that can be stored in the undo stack.

Declaration
public ulong undoLimit { get; set; }
Property Value
Type Description
ulong

Methods

BeginMacro(string)

Begins composition of a macro command with the given text description.

An empty command described by the specified text is pushed on the stack. Any subsequent commands pushed on the stack will be appended to the macro command's children until EndMacro() is called.

While a macro is being composed, the stack is disabled. This means that:
- Events are not emitted.
- canRedo and canUndo will always return false.
- Calling Undo() or Redo() has no effect.
The stack is re-enabled when the macro is ended.

Declaration
public void BeginMacro(string name)
Parameters
Type Name Description
string name

The name of the macro command.
Remarks

Nested calls to BeginMacro(string) are supported, but every call to BeginMacro(string) must have a corresponding call to EndMacro().

Examples
undoStack.BeginMacro("Insert Red Text");
undoStack.Push(new InsertText(...));
undoStack.Push(new SetRedText(...));
undoStack.EndMacro();
var insertRedText = new UndoCommand("Insert Text");
new InsertText(..., insertRedText);
new SetRedText(..., insertRedText);
undoStack.Push(insertRedText);
See Also

Clear()

Clears the undo and redo stacks.

Declaration
public void Clear()

EndMacro()

Ends composition of a macro command.
If this is the outermost macro in a set nested macros, this function emits indexChanged once for the entire macro command.

Declaration
public void EndMacro()
Exceptions
Type Condition
InvalidOperationException

Thrown if no macro is being composed.
See Also

Push(UndoCommand)

Pushes the given command on the undo stack.

Declaration
public void Push(UndoCommand command)
Parameters
Type Name Description
UndoCommand command

The command to push.
Remarks

If the current command is a macro command, the pushed command is added to the macro.

Redo()

Calls Redo() on the last command in the redo stack.

Declaration
public void Redo()

ResetClean()

Sets the clean state to -1.

Declaration
public void ResetClean()

SetClean()

Sets the clean state to the last command in the undo stack.

Declaration
public void SetClean()

Undo()

Calls Undo() on the last command in the undo stack.

Declaration
public void Undo()

Events

cleanStateChanged

Emitted when the clean state changes.

Declaration
public event Action cleanStateChanged
Event Type
Type Description
Action

indexChanged

Emitted the current Command index changes.

Declaration
public event Action<int> indexChanged
Event Type
Type Description
Action<int>