EventHandler Not Detecting KeyDown

Question

I am trying to use EventHandler to detect KeyDown within a LocatorPane. Anytime I press a key inside the LocatorPane the proper action is not executed (doesn't matter which key I choose) but rather the the symbol of the key pressed appears in the next input line below the LocatorPane (i.e. it jumps out of the LocatorPane). I must be missing something simple because this works fine with {{"MouseClicked",2} :> (AppendTo[someList, 1]; Print[someList])} but not as shown below with {{"KeyDown", a} :> (AppendTo[someList, 1]; Print[someList])}. Btw, in case it's not obvious I am using the right mouse button for the click because the LocatorPane responds to the left button. Any suggestions on getting this to work properly with KeyDown? - GR

(* code below does not respond to "KeyDown" events but will respond properly to    
 "MouseClicked" *)     

pts = {};

someList = {};

EventHandler[



 LocatorPane[Dynamic[pts], Graphics[Circle[], ImageSize -> 500], 
  LocatorAutoCreate -> True, 
  Appearance -> {Graphics[{Red, Disk[]}, ImageSize -> 10], 
    Graphics[{Blue, Disk[]}, ImageSize -> 10]}],

 {{"KeyDown", "a"} :> (AppendTo[someList, 1]; Print[someList])}

 ]

Answer 1

This is only a partial answer but may help.

See here for related case, it is probable that KeyDown "a" is reserved like "c".

This does not work:

DynamicModule[{someList = {}},
  EventHandler[Graphics[{Blue, Disk[]}, ImageSize -> 100], 
     {{"KeyDown", "a"} :> (AppendTo[someList, 1]; Print[someList])}]]
(** doesn't work **)

But changing "a" to "x" does work"

DynamicModule[{someList = {}},
  EventHandler[Graphics[{Blue, Disk[]}, ImageSize -> 100], 
     {{"KeyDown", "x"} :> (AppendTo[someList, 1]; Print[someList])}]]
(** does work **)

Answer 2

another idea but not an answer...

DynamicModule[{keyList = {}, pts = {}, input = Null},
 EventHandler[
  {LocatorPane[Dynamic[pts],
     Graphics[Circle[], ImageSize -> 500],
     LocatorAutoCreate -> True,
     Appearance -> {Graphics[{Red, Disk[]}, ImageSize -> 10], 
       Graphics[{Blue, Disk[]}, ImageSize -> 10]}
     (*LocatorPane**)],
    Dynamic@keyList,
    Dynamic@pts,
    InputField@Dynamic@input (* 
    place cursor in input field after evaluation *)
    } // Column,
  {{"KeyDown", "a"} :> (AppendTo[keyList, "a"]; Speak["a"]),
   {"KeyDown", "b"} :> (AppendTo[keyList, "b"]; Speak["b"]),
   {"KeyDown", "c"} :> (AppendTo[keyList, "c"]; Speak["c"])
   } , PassEventsDown -> True (*EventHandler**)]
 (*DynamicModule**)]

Edit1:

Probably this is a solution for your problem. Instead of EventHandler I tried CellEventActions with SelectionMove

DynamicModule[{pts = {}, keyAction},

 keyAction = CellPrint@ExpressionCell[#,

      Deployed -> True,
     (* especially no text cursor *)

     CellEventActions -> {
       {"KeyDown", "a"} :> Speak@"a",
       {"KeyDown", "b"} :> Speak@"b",
       "KeyDown" :> Null
       }(*ExpressionCell**)] &;

 LocatorPane[Dynamic[pts],
   Graphics[Circle[], ImageSize -> 500],
   LocatorAutoCreate -> True,
   Appearance -> {Graphics[{Red, Disk[]}, ImageSize -> 10], 
     Graphics[{Blue, Disk[]}, ImageSize -> 10]}
   (*LocatorPane*)] // keyAction

 (*DynamicModule**)]; SelectionMove[
 InputNotebook[], Before, CellContents];

I hope, it meets your needs. I'm not quite sure, but this new version should work in: M7,M8,M9,M10

Answer 3

You can do the following as a workaround in M9.

 EventHandler["t",{"KeyDown":>
   If[CurrentValue["EventKey"]=="a",
     Print["a"]
   ]
  }
 ]

Answer 4

From tutorial/InteractiveGraphicsPalette

you can see that quite a few of the lowercase keys are used by DrawingTools which becomes active once the cursor focus is on the graphics. So, the easiest work-around is to use uppercase letters in your EventHandler as suggested by pjc42.

When the first argument of EventHandler does not contain a graphics object, this issue does not arise:

DynamicModule[{someList = {}}, 
             EventHandler[Style["TEXT", 64,  Background -> Red],
                      {{"KeyDown", "a"} :> (AppendTo[someList, 1];  Print[someList])}]]