keydown EventListener Firing Twice For Some Keys

[jduncan]

Hey, any idea why the "keydown" event listener would be firing twice for certain keys (e.g. arrow key). I'm trying to adjust the listbox selection with the up and down arrow keys while inside the edittext box. Everything works but it fires twice and moves the selection down two spots.

Example code below... Thanks for any help!

// setup the dialog
var arr = ["Option 1", "Option 2", "Option 3", "Option 4", "Option 5", "Option 6"];
var win = new Window("dialog");
var text = win.add("edittext");
text.active = true;
var list = win.add("listbox", undefined, arr);
list.selection = 0;

// move list selection with arrow keys while in edittext
text.addEventListener("keydown", function (k) {
  alert("Pressed Key: " + k.keyName);
  if (k.keyName == "Up") {
    list.selection = list.selection.index - 1;
  } else if (k.keyName == "Down") {
    list.selection = list.selection.index + 1;
  }
});

win.show();

[m1b · Accepted solution]

Hi @jduncan, I'm not sure why it fires twice, but you can fix it by adding "k.preventDefault();" into your listener.

- Mark

Edit: to clarify—don't preventDefault on all keydown events, just the ones you are targetting:

w.addEventListener("keydown", function (k) {
    if (k.keyName == "Up") {
        listbox.selection = listbox.selection.index - 1;
        k.preventDefault();
    } else if (k.keyName == "Down") {
        listbox.selection = listbox.selection.index + 1;
        k.preventDefault();
    }
});

[jduncan]

Yep, that's exactly what I used as a workaround, I was just curious if anyone knew why it fired twice.

And, I learned the hard way that I shouldn't preventDefault() all of the keys #facepalm!

Thanks so much for your help!

[CarlosCanto]

are you guys on mac? I'm on windows and the original script works just fine. up/down keys move one spot at a time without preventDefault()

[m1b]

Yeah I'm on Mac and I get the double-firing.

[m1b]

Hey @CarlosCanto, does it break on Windows when you add the preventDefault ?

[CarlosCanto]

Hi Mark, no it doesn't break after adding preventDefault(). 

[CarlosCanto]

...however, using preventDefault() helps by stopping the cursor from moving left/right, which is the default behaviour when pressing up/down keys while in the text box

[jduncan]

Yep, I'm on a Mac as well.