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use crate::{
BoxConstraints, Data, Env, Event, EventCtx, LayoutCtx, LifeCycle, LifeCycleCtx, PaintCtx,
Point, Rect, Size, UpdateCtx, Widget, WidgetPod,
};
type ChildPicker<T, U> = dyn Fn(&T, &Env) -> U;
type ChildBuilder<T, U> = dyn Fn(&U, &T, &Env) -> Box<dyn Widget<T>>;
pub struct ViewSwitcher<T, U> {
child_picker: Box<ChildPicker<T, U>>,
child_builder: Box<ChildBuilder<T, U>>,
active_child: Option<WidgetPod<T, Box<dyn Widget<T>>>>,
active_child_id: Option<U>,
}
impl<T: Data, U: PartialEq> ViewSwitcher<T, U> {
pub fn new(
child_picker: impl Fn(&T, &Env) -> U + 'static,
child_builder: impl Fn(&U, &T, &Env) -> Box<dyn Widget<T>> + 'static,
) -> Self {
Self {
child_picker: Box::new(child_picker),
child_builder: Box::new(child_builder),
active_child: None,
active_child_id: None,
}
}
}
impl<T: Data, U: PartialEq> Widget<T> for ViewSwitcher<T, U> {
fn event(&mut self, ctx: &mut EventCtx, event: &Event, data: &mut T, env: &Env) {
if let Some(child) = self.active_child.as_mut() {
child.event(ctx, event, data, env);
}
}
fn lifecycle(&mut self, ctx: &mut LifeCycleCtx, event: &LifeCycle, data: &T, env: &Env) {
if let LifeCycle::WidgetAdded = event {
let child_id = (self.child_picker)(data, env);
self.active_child = Some(WidgetPod::new((self.child_builder)(&child_id, data, env)));
self.active_child_id = Some(child_id);
}
if let Some(child) = self.active_child.as_mut() {
child.lifecycle(ctx, event, data, env);
}
}
fn update(&mut self, ctx: &mut UpdateCtx, _old_data: &T, data: &T, env: &Env) {
let child_id = (self.child_picker)(data, env);
if Some(&child_id) != self.active_child_id.as_ref() {
self.active_child = Some(WidgetPod::new((self.child_builder)(&child_id, data, env)));
self.active_child_id = Some(child_id);
ctx.children_changed();
}
if let Some(child) = self.active_child.as_mut() {
child.update(ctx, data, env);
}
}
fn layout(&mut self, ctx: &mut LayoutCtx, bc: &BoxConstraints, data: &T, env: &Env) -> Size {
match self.active_child {
Some(ref mut child) => {
let size = child.layout(ctx, bc, data, env);
child.set_layout_rect(ctx, data, env, Rect::from_origin_size(Point::ORIGIN, size));
size
}
None => bc.max(),
}
}
fn paint(&mut self, ctx: &mut PaintCtx, data: &T, env: &Env) {
if let Some(ref mut child) = self.active_child {
child.paint_raw(ctx, data, env);
}
}
}