Events and Actions

Events and actions

An event is something that happens, such as a click, typing or the screen opening. You attach actions (built-in steps) and optionally a script to it. Select a control and open the Events tab, or click Screen settings for the screen's own events.

Which events exist

Control	Events
Button	click
Text Box	text_changed (each edit), submit (Enter)
Checkbox	checked, unchecked
Slider, Dropdown	value_changed
Item List	item_click, item_primary, item_secondary (value = row index)
Every control	hover, mouse_enter, mouse_leave (client only, at most 4 per second)
Screen	open, close, tick, key (tick and key are client only)

Timers and keys

Two screen events make games, clocks and animations possible without any hover tricks:

• tick runs on the player's screen every few milliseconds while the screen is open. Set how often with Tick interval (ms) in Screen settings (50–60000; 0 turns it off). If a run is still going when the next one is due, the next one waits.
• key runs on the player's screen for each key pressed while no text box is being typed in. A script receives the key's name as ctx.value: a–z, 0–9 (number row and keypad), space, enter, tab, backspace, left, right, up, down, f1–f12. Escape is never sent; it always closes the screen. Holding a key repeats it every Key repeat (ms) (Screen settings, 150 by default; 0 means a held key sends one event), and a script can tell a held key from a fresh press with ctx.repeat. Presses never pile up: a key arriving while the previous event is still running is dropped, so holding a key can't queue a backlog of moves.

Both work in Preview too. They can only use Client actions or a client script, because they fire far too often for the server. For server work, have the script show a button the player clicks, or use a control event. Export the project again after updating Arcadia Studio so the game gets the runtime the editor bundles.

Sounds on events

Choose play_sound as an action and a sound picker appears. Pick one of the project's sounds, click Import… to add a file right there, or type a Minecraft sound ID such as minecraft:ui.button.click. It plays whenever the event fires. Minecraft sounds only play in Minecraft.

Web and desktop events

With advanced tools a screen also has input_pressed, input_released and animation_end, and physics bodies have collide, collide_stay and collide_end, plus trigger_enter, trigger_stay and trigger_exit for triggers. Stay events repeat every 250 ms. They run on the player's screen only.

Client and Server

Every event has two sides:

• Client: "Runs locally for this screen." Instant visual changes on the player's own screen.
• Server: "Trusted server actions. Preview simulates these." Runs on the Minecraft server: commands, messages, navigation, server scripts.

When an event fires, client actions run first on the player's screen, then the server is told which control and event fired, and the server runs its own actions from its own copy of your project. A modified client can't invent server actions or commands.

Adding actions

In the Events panel, pick the event, then under Client or Server click + Add action, choose a Type, and fill in Target and Value. Remove deletes an action. Actions run top to bottom.

Client actions

Type	Target	Value	Does
set_text	control Id	new text	Changes a control's text. ${var} works.
set_visible	control Id	true / false	Shows or hides a control.
set_enabled	control Id	true / false	Enables or disables a control.
set_value	control Id	new value	Sets a slider, checkbox, text box, progress bar or dropdown value.
change_texture	control Id	image resource	Swaps a control's image.
set_variable	variable name	value	Sets a screen variable.
toggle_variable	variable name	–	Flips a true/false variable.
play_sound	–	sound ID	Plays a sound, for example minecraft:ui.button.click.
message	–	text	Shows a message to the player.
open_ui	–	screen ID	Asks to switch to another screen.
close_ui	–	–	Closes the screen.

Server actions

Type	Target	Value	Does
command	–	command	Runs a Minecraft command as the player, with the player's permissions. The command is used exactly as written; player input is never inserted into it.
message	–	text	Sends the player a chat message. ${var} works.
set_variable / toggle_variable	variable	value	Changes the server's copy of a variable.
open_ui	–	screen ID	Opens another screen of this project. (To open another project's screen, use a server script: ctx.ui.open("project:screen").)
close_ui	–	–	Closes the screen.
player_inventory	Item List Id	–	Fills an Item List with the player's inventory.
server_function	function ID	argument	Calls a function registered by a mod or KubeJS. See [[Addon API

Permission level and cooldown (Server side)

Each Server handler has:

• Permission level: 0 — Everyone, 1 — Moderator, 2 — Operator, 3 — Administrator, 4 — Owner. Players below it can't trigger the server side of this event.
• Minimum interval (ticks): a per-player cooldown, 0–1200 ticks (20 ticks = 1 second). The default is 4. Reopening the screen doesn't reset it. Text and slider changes aren't delayed by it, so the final value always arrives.

Both are enforced by the server.

Scripts on events

Instead of (or as well as) actions, an event can run a JavaScript function. In the Events panel use New Script, write the function, then Save & Assign. See Scripting for the full workflow and API.

Variables

• Each screen has string variables, with starting values set in Screen settings.
• Show them in text with ${name}, and use them in conditions.
• Variables reset every time the screen opens; they aren't saved between sessions.
• Client and server each keep their own copy. The server mirrors trusted client changes (visibility, enabled state, variables) so it can check what's allowed. Server-side changes reach the client through script UI calls such as ctx.ui.setVariable.
• The player's input is available on the server as event_value (and ctx.value in scripts). It can be shown in messages but is never put into commands.

Navigation between screens

Use open_ui with a screen ID from the same project; validation checks that the screen exists. A server script can also open another project's screen with ctx.ui.open("project_id:screen_id"). Navigation from the client side is a request; the server decides.