Implementing undo for nested transactions

theswamp

• • 1. namespace Namespace1

    2. {

    3. public static class Commands

    4. {

    6. /// Example: Sub-command undo

    7. ///

    8. /// This is the simplest way to implement

    9. /// individually-undoable steps within a

    10. /// command that repetitively prompts for

    11. /// input and creates geometry immediately

    12. /// after each input request.

    14. [CommandMethod( "SUBUNDOEXAMPLE" )]

    15. public static void UndoGroupExample()

    16. {

    17. Document doc = Application.DocumentManager.MdiActiveDocument;

    18. Database db = doc.Database;

    19. ObjectId ms = SymbolUtilityServices.GetBlockModelSpaceId( db );

    20. PromptPointOptions ppo = new PromptPointOptions( "\nPick center point: " );

    21. ppo.AllowNone = true; // allow exit via ENTER

    22. ppo.Keywords.Add( "Undo" );

    23. Keyword undoKeyword = ppo.Keywords[0];

    24. var transmgr = doc.TransactionManager;

    25. Stack<Entity> circles = new Stack<Entity>();

    26. using( Transaction outer = transmgr.StartTransaction() )

    27. {

    28. transmgr.EnableGraphicsFlush( true );

    29. while( true )

    30. {

    31. undoKeyword.Enabled = circles.Count > 0;

    32. PromptPointResult ppr = doc.Editor.GetPoint( ppo );

    33. switch( ppr.Status )

    34. {

    35. case PromptStatus.Cancel: // ESC exit roll back everything

    36. return;

    37. case PromptStatus.None: // ENTER exit and commit changes

    38. outer.Commit();

    39. return;

    40. case PromptStatus.Keyword: // Undo the last circle

    41. if( circles.Count > 0 )

    42. {

    43. UpdateDisplay( () => circles.Pop().Erase() ); // see below

    44. }

    45. else

    46. doc.Editor.WriteMessage( "\nNothing to undo" );

    47. continue;

    48. }

    49. if( ppr.Status != PromptStatus.OK )

    50. throw new InvalidOperationException( "Unexpected result" );

    51. using( Transaction tr = transmgr.StartTransaction() )

    52. {

    53. BlockTableRecord model = (BlockTableRecord)

    54. tr.GetObject( ms, OpenMode.ForWrite ) as BlockTableRecord;

    55. Circle circle = new Circle( ppr.Value, Vector3d.ZAxis, 1.0 );

    56. try

    57. {

    58. circle.SetDatabaseDefaults( db );

    59. model.AppendEntity( circle );

    60. }

    61. catch

    62. {

    63. circle.Dispose();

    64. throw;

    65. }

    66. transmgr.AddNewlyCreatedDBObject( circle, true );

    67. circles.Push( circle );

    68. transmgr.QueueForGraphicsFlush();

    69. tr.Commit();

    70. doc.Editor.UpdateScreen();

    71. }

    72. }

    73. }

    74. }

    76. /// Helper:

    77. ///

    78. /// Executes caller-supplied delegate within a

    79. /// transaction and updates the display:

    81. public static void UpdateDisplay( Action action )

    82. {

    83. Document doc = Application.DocumentManager.MdiActiveDocument;

    84. if( doc == null )

    85. throw new InvalidOperationException( "no document" );

    86. var transmgr = doc.TransactionManager;

    87. transmgr.EnableGraphicsFlush( true );

    88. using( Transaction tr = transmgr.StartTransaction() )

    89. {

    90. action();

    91. transmgr.QueueForGraphicsFlush();

    92. tr.Commit();

    93. doc.Editor.UpdateScreen();

    94. }

    95. }

    96. }

    97. }