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CurrentValue and FrontEndTokens

As mentioned briefly under Highly Useful Functionality ▶ Kernels and Remote Computations Mathematica has a device called a FrontEndToken for accessing front end methods and information.

FrontEndToken

In general, how this is structured is the following:

 FrontEndToken[token_String]

or

 FrontEndToken[feobject_,token_String]

And then the front end is actually accessed via FrontEndExecute . We can use this to, say, copy the previous cell as plaintext and paste it:

 SelectionMove[PreviousCell@PreviousCell[],All,Cell];
FrontEndTokenExecute["CopySpecial","Text"];
SelectionMove[EvaluationCell[],After,Cell];
FrontEndTokenExecute["Paste"];

Via front end tokens, it’s possible to do pretty much everything the front end can. A somewhat exhaustive list of them is presented below:

Each button in that list executes FrontEndTokenExecute[token] so test them out for yourself. Beware that many might be dangerous.

You may know or recall that there are a series of event specifications that can be passed to EventHandler , CellEventActions , NotebookEventActions , and FrontEndEventActions . There are a number of documented event specifications, but there is one critical class of these that is missing. It looks like this:

 {"MenuCommand",token_}

This catches the front end event called by FrontEndTokenExecute[token] . Among the many uses of this, it can be used for changing the way an InputField evaluates using the "HandleShiftReturn" token:

 validationFunction[variable_]:=
 (variable=StringReplace[variable,Except[DigitCharacter]->""]);
validationFunction~SetAttributes~HoldFirst;
InputField[Dynamic[var],String]~EventHandler~{ {"MenuCommand","HandleShiftReturn"}:>validationFunction[var]}

Now whenever you press SHIFT+ENTER , validationFunction is applied. This is useful if you don’t want to put your side-effects as the second argument to Dynamic .

This can also be used to make notebooks with custom actions, for, say, a save event:

 CreateDocument[{
  Cell["","TopBarCell"],
  Cell["Try saving this notebook","Text"]},
 NotebookEventActions{
  {"MenuCommand","Save"}⧴
  FrontEndExecute@
  FrontEnd`AttachCell[
   First@Cells[],
   Cell[TextData[{"Notebook cannot be saved via the front end. Try ",ToBoxes@Unevaluated@Style[NotebookSave[],"Input"]}],"Text",FontColorRed],
   {Automatic,{Left,Bottom}},
   {Left,Top},
   "ClosingActions"{"OutsideMouseClick"}
   ],
  {"MenuCommand","SaveRename"}⧴
  FrontEndExecute@
  FrontEnd`AttachCell[
   First@Cells[],
   Cell[TextData[{"Notebook cannot be deleted via the front end. Try ",ToBoxes@Unevaluated@Style[NotebookClose[],"Input"]}],"Text",FontColorRed],
   {Automatic,{Left,Bottom}},
   {Left,Top},
   "ClosingActions"{"OutsideMouseClick"}
   ]
  },
 StyleDefinitions
 Notebook[{
   Cell[StyleData[StyleDefinitions"Default.nb"]],
   Cell[StyleData["TopBarCell"],
    CellMargins{ {0, 0}, {15, 0}},
    CellFrame{ {0,0},{2,0}},
    "CellFrameStyle"GrayLevel[.8],
    BackgroundGrayLevel[.9]
    ]
   }],
 WindowSize{500,400}]

CurrentValue

In many ways, CurrentValue is just a wrapper to Options , SetOptions , and FrontEndToken but this makes it powerful.

For instance, we can use it to query style options:

 CurrentValue@{"StyleDefinitions","Section","Background"}

Figure out what the current selection in a notebook is (restricted to content):

 SelectionMove[EvaluationCell[],All,CellContents];
    CurrentValue@"SelectionData"

 RowBox[{RowBox[{RowBox[{"SelectionMove","[",RowBox[{RowBox[{"EvaluationCell","[","]"}],",","All",",","CellContents"}],"]"}],";"}],"
",RowBox[{"CurrentValue","@","\"SelectionData\""}]}]

And determine whether a modifier key is pressed or not:

 Dynamic@CurrentValue["ShiftKey"]

It can also be used to set options:

 CurrentValue[EvaluationCell[],"Background"]=RandomColor[];
Pause[.5];
CurrentValue[EvaluationCell[],"Background"]=None;