Trait VarSubscribe

pub trait VarSubscribe<T>: Var<T> + AnyVarSubscribe
where
    T: VarValue,
{
    // Required method
    fn subscribe_when(
        &self,
        op: UpdateOp,
        widget_id: WidgetId,
        predicate: impl Fn(&T) -> bool + Send + Sync + 'static,
    ) -> VarHandle;

    // Provided methods
    fn on_pre_new<H>(&self, handler: H) -> VarHandle
       where H: AppHandler<OnVarArgs<T>> { ... }
    fn on_new<H>(&self, handler: H) -> VarHandle
       where H: AppHandler<OnVarArgs<T>> { ... }
}

Extension methods to subscribe any widget to a variable or app handlers to a variable.

Also see WIDGET methods for the primary way to subscribe from inside a widget.

Required Methods

fn subscribe_when( &self, op: UpdateOp, widget_id: WidgetId, predicate: impl Fn(&T) -> bool + Send + Sync + 'static, ) -> VarHandle

Register the widget to receive an UpdateOp when this variable is new and the predicate approves the new value.

Variables without the NEW capability return VarHandle::dummy.

Provided Methods

fn on_pre_new<H>(&self, handler: H) -> VarHandle

where H: AppHandler<OnVarArgs<T>>,

Add a preview handler that is called every time this variable updates, the handler is called before UI update.

Note that the handler runs on the app context, all ContextVar<T> used inside will have the default value.

fn on_new<H>(&self, handler: H) -> VarHandle

where H: AppHandler<OnVarArgs<T>>,

Add a handler that is called every time this variable updates, the handler is called after UI update.

Note that the handler runs on the app context, all ContextVar<T> used inside will have the default value.

Object Safety

This trait is not object safe.

Implementors

impl<T, V> VarSubscribe<T> for V

where T: VarValue, V: Var<T>,