Events

Connect callbacks and userdata

Gui:Signal callbacks receive a borrowed widget and the data pointer supplied at registration. Keep that data alive until all registered users are disconnected or destroyed. The API does not copy arbitrary userdata.

import gui
let connect_button = fn (button:u8*, label:u8*) -> u64 {
    return Gui:on_click(button, fn (widget:u8*, data:u8*) -> void {
        Gui:label_text(data, "Clicked")
    }, label)
}

Keep callback data alive

The label must remain alive while the button can emit the callback. on_activate handles input activation; on_text_changed observes edits; key and mouse event callbacks return nonzero when handled or zero to allow normal processing.

Timers and idle sources

import gui
let schedule_refresh = fn (label:u8*) -> u32 {
    return Gui:timer(1000, fn (data:u8*) -> i32 {
        Gui:label_text(data, "Updated")
        return 1
    }, label)
}
let cancel_refresh = fn (source:u32) -> void { Gui:source_remove(source) }

A timer returns nonzero to continue or zero to remove itself. idle uses the same callback shape when the loop is idle. Store the source identifier and remove an active source before destroying the state or widgets it references. Removing identifier zero is safe. Do not later remove an already expired identifier as though it still named your source.

Keep the event loop responsive

Run long operations outside event callbacks and marshal UI updates back through the event loop. A short timer interval does not make blocking work asynchronous.