Events

Sending events to the host

A document never changes your app's data. It asks, with event:

Flex {
  mouse_down: fn () {
    event("tool_selected", tool_name);
  },
  children: [ Text { text: tool_name } ],
}

The host registers a handler for each name. See Typed bindings for declaring events so a typo is caught at load.

Pointer listeners

Flex and Grid accept mouse_down, mouse_up, mouse_enter and mouse_leave. Enter and leave fire on the transition, for every widget on the path from the root to the deepest hit.

Key chords

keydown takes a map from chord to handler. Modifiers join with _:

Flex {
  keydown: {
    ctrl_k: fn () { event("palette"); },
    escape: fn () { event("close"); },
  },
  children: [],
}

A chord with Ctrl, Alt or Meta goes to the focused listeners first, innermost first. A bare key goes to the tree first.

Controls

Slider {
  value: volume, min: 0, max: 100, step: 5,
  on_change: fn (v: float) { event("set_volume", v); },
  on_commit: fn (v: float) { event("save_volume", v); },
  style: { width: "grow", height: 16 },
}

Controls are controlled: the document supplies value on every render, and the widget reports what the pointer asked for.

TextInput reports on_change on every edit, on_submit on Enter, and on_blur when focus leaves by any route.

TODO: drag and drop, context menus, scroll, pointer capture.