UndoChangeRequest

java.lang.Object
- ptolemy.kernel.util.ChangeRequest
- - ptolemy.kernel.undo.UndoChangeRequest

```
public class UndoChangeRequest
extends ChangeRequest
```
A change request to undo. When executed, this change request will identify the undo stack associated with the specified context, and it will execute the top undo action on that stack, if there is one.

Since:

Ptolemy II 3.1

Version:

$Id$

Author:

Edward A. Lee and Neil Smyth

Pt.AcceptedRating:

Green (hyzheng)

Pt.ProposedRating:

Green (eal)

Constructor Summary

Constructors
Constructor	Description
`UndoChangeRequest(java.lang.Object originator, NamedObj context)`	Construct a change request to be executed in the specified context.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`protected void`	`_execute()`	Execute the change by invoking undo on the undo stack of the context specified in the constructor.
`NamedObj`	`getContext()`	Return the context specified in the constructor, or null if none was specified.

Methods inherited from class ptolemy.kernel.util.ChangeRequest
addChangeListener, execute, getDescription, getLocality, getSource, isErrorReported, isPersistent, isStructuralChange, removeChangeListener, setDescription, setErrorReported, setListeners, setPersistent, waitForCompletion

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Constructor Detail
  - UndoChangeRequest
```
public UndoChangeRequest(java.lang.Object originator,
                         NamedObj context)
```
    Construct a change request to be executed in the specified context. The undo stack associated with the specified context will be used. That stack is the one returned by UndoStackAttribute.getUndoInfo().
    
    Parameters:
    
    originator - The originator of the change request.
    
    context - The context in which to execute the MoML.
    
    See Also:
    
    UndoStackAttribute
- Method Detail
  - getContext
```
public NamedObj getContext()
```
    Return the context specified in the constructor, or null if none was specified.
    
    Returns:
    
    The context.
  - _execute
```
protected void _execute()
                 throws java.lang.Exception
```
    Execute the change by invoking undo on the undo stack of the context specified in the constructor.
    
    Specified by:
    
    _execute in class ChangeRequest
    
    Throws:
    
    java.lang.Exception - If an exception is thrown while evaluating the request.