Are We There Yet?

Not quite. We know there is a problem with an Undo that tries to Undo too much. We know how to fix it: we ll just check whether the stack is empty, and if it isn t, we ll do nothing. But we need a test ”let s add one more *undo to the undo.test file:

 *enter 
 *type abc 
 *output 
 <P>abc</P> 
 *end 
 *undo 
 *output 
 <P>ab</P> 
 *end 
 *undo 
 *output 
 <P>a</P> 
 *end 
 *undo 
 *output 
 <P></P> 
 *end 
 *undo 
 *output 
 
 *end  *undo *output  *end  

This fails, predictably, with the message Stack Empty . Now we can add the feature:

 public void Restore() { 
  if (SavedModels.Count == 0) return;  
 TextModel savedModel = (TextModel) SavedModels.Pop(); 
 lines = savedModel.Lines; 
 selectionStart = savedModel.SelectionStart; 
 } 

The tests all run. I believe that functionality is now complete. Let s reflect. In the next chapter ”Chapter 29, The Final Optimized Undo ”we ll turn our attention to efficiency.