Define a custom widget type — widget • termr

widget() creates a new widget type and returns its constructor. All behaviour is given as plain functions that receive the widget as their first argument, self.

Usage

widget(
  name,
  state = list(),
  render = NULL,
  compose = NULL,
  bindings = list(),
  actions = list(),
  on = list(),
  methods = list(),
  style = NULL,
  focusable = FALSE,
  inherit = Widget
)

Arguments

name: Type name (used by type selectors, e.g. app$query("Counter")).
state: A named list of state fields. Values created with reactive() can have a watcher; plain values are reactive too. Fields are read and assigned as self$<name>.
render: function(self) returning the content: a string, a character vector of lines or span()s.
compose: function(self) returning a list of child widgets.
bindings: A list of bind() key bindings.
actions: A named list of function(self); bindings refer to them by name.
on: A named list of event handlers function(self, event), e.g. list(mount = ..., "button.pressed" = ...).
methods: A named list of extra methods function(self, ...), callable as widget$<name>(...).
style: Default style() of the type.
focusable: Can widgets of this type receive focus?
inherit: Parent class: Widget, Vertical or Horizontal.

Value

A constructor function function(..., id = NULL, classes = NULL, style = NULL, disabled = FALSE). Named arguments in ... set initial state values; unnamed arguments are child widgets.

Examples

Counter <- widget(
  "Counter",
  state = list(count = reactive(0L)),
  render = function(self) sprintf("Count: %d", self$count),
  bindings = list(bind("up", "increment"), bind("down", "decrement")),
  actions = list(
    increment = function(self) self$count <- self$count + 1L,
    decrement = function(self) self$count <- self$count - 1L
  ),
  focusable = TRUE
)
counter <- Counter(count = 5L)
counter$count
#> [1] 5
render_widget(counter, 12, 1)
#> <ScreenBuffer 12x1>
#> +------------+
#> |Count: 5    |
#> +------------+