Struct druid::LensWrap

pub struct LensWrap<U, L, W> { /* fields omitted */ }

A wrapper for its widget subtree to have access to a part of its parent's data.

Every widget in druid is instantiated with access to data of some type; the root widget has access to the entire application data. Often, a part of the widget hierarchy is only concerned with a part of that data. The LensWrap widget is a way to "focus" the data reference down, for the subtree. One advantage is performance; data changes that don't intersect the scope of the lens aren't propagated.

Another advantage is generality and reuse. If a widget (or tree of widgets) is designed to work with some chunk of data, then with a lens that same code can easily be reused across all occurrences of that chunk within the application state.

This wrapper takes a Lens as an argument, which is a specification of a struct field, or some other way of narrowing the scope.

Implementations

impl<U, L, W> LensWrap<U, L, W>

pub fn new(inner: W, lens: L) -> LensWrap<U, L, W>

Wrap a widget with a lens.

When the lens has type Lens<T, U>, the inner widget has data of type U, and the wrapped widget has data of type T.

Trait Implementations

impl<T, U, L, W> Widget<T> for LensWrap<U, L, W> where
    T: Data,
    U: Data,
    L: Lens<T, U>,
    W: Widget<U>, 

fn event(&mut self, ctx: &mut EventCtx, event: &Event, data: &mut T, env: &Env)

Handle an event.

fn lifecycle(
    &mut self,
    ctx: &mut LifeCycleCtx,
    event: &LifeCycle,
    data: &T,
    env: &Env
)

Handle a life cycle notification.

fn update(&mut self, ctx: &mut UpdateCtx, old_data: &T, data: &T, env: &Env)

Handle a change of data.

fn layout(
    &mut self,
    ctx: &mut LayoutCtx,
    bc: &BoxConstraints,
    data: &T,
    env: &Env
) -> Size

Compute layout.

fn paint(&mut self, ctx: &mut PaintCtx, data: &T, env: &Env)

Paint the widget appearance.

fn id(&self) -> Option<WidgetId>