Nice keyboard inputs in Elm.
It is quite tedious to find out the currently pressed down keys with just the Keyboard module, so this package aims to make it easier.
You can use Keyboard.Extra in two ways:
- The "Msg and Update" way, which has some setting up to do but has a bunch of ways to help you get the information you need.
- The "Plain Subscriptions" way, where you get subscriptions for keys' down and up events, and handle the rest on your own.
- Main example shows most of the basic usage
- Arrows Direction example shows how the
North,NorthEast, etc. directions work - Tracking Key Changes example uses
updateWithKeyChangeto show when a key is pressed down and when it is released - Plain Subscriptions example is for the more experienced Elm users, who wish to get more "down to the metal" with just subscribing to keyboard events
All of the examples are also in the example directory in the repository.
If you use the "Msg and Update" way, you will get the most help, such as:
- All keyboard keys are named values of the
Keytype, such asArrowUp,CharAandEnter - You can find out whether e.g.
Shiftis pressed down when any kind of aMsghappens in your program - Arrow keys and WASD can be used as
{ x : Int, y : Int }or as a union type (e.g.South,NorthEast) - You can also get a full list of keys that are pressed down
When using Keyboard.Extra like this, it follows The Elm Architecture. Its model is a list of keys, and it has an update function and some subscriptions. Below are the necessary parts to wire things up. Once that is done, you can get useful information using the helper functions such as arrows and arrowsDirection.
Include the list of keys in your program's model
import Keyboard.Extra exposing (Key)
type alias Model =
{ pressedKeys : List Key
-- ...
}
init : ( Model, Cmd Msg )
init =
( { pressedKeys = []
-- ...
}
, Cmd.none
)Add the message type in your messages
type Msg
= KeyMsg Keyboard.Extra.Msg
-- ...Include the subscriptions for the events to come through (remember to add them in your main too)
subscriptions : Model -> Sub Msg
subscriptions model =
Sub.batch
[ Sub.map KeyMsg Keyboard.Extra.subscriptions
-- ...
]
And finally, you can use update to have the list of keys be up to date
update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
case msg of
KeyMsg keyMsg ->
( { model | pressedKeys = Keyboard.Extra.update keyMsg model.pressedKeys }
, Cmd.none
)
-- ...Now you can get all the information anywhere where you have access to the model, for example like so:
calculateSpeed : Model -> Float
calculateSpeed model =
let
arrows =
Keyboard.Extra.arrows model.pressedKeys
in
model.currentSpeed + arrows.x
isShooting : Model -> Bool
isShooting model =
List.member Space model.pressedKeysHave fun! :)
PS. The Tracking Key Changes example example shows how to use updateWithKeyChange to find out exactly which key was pressed down / released on that update cycle.
With the "plain subscriptions" way, you get the bare minimum:
- All keyboard keys are named values of the
Keytype, such asArrowUp,CharAandEnter
Setting up is very straight-forward:
type Msg
= KeyDown Key
| KeyUp Key
-- ...
subscriptions : Model -> Sub Msg
subscriptions model =
Sub.batch
[ Keyboard.Extra.downs KeyDown
, Keyboard.Extra.ups KeyUp
-- ...
]There's an example for this, too: Plain Subscriptions
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