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// Copyright 2020 The Druid Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//! A widget that can dynamically switch between one of many views.
use crate::widget::prelude::*;
use crate::{Data, Point, WidgetPod};
use tracing::instrument;
type ChildPicker<T, U> = dyn Fn(&T, &Env) -> U;
type ChildBuilder<T, U> = dyn Fn(&U, &T, &Env) -> Box<dyn Widget<T>>;
/// A widget that switches dynamically between multiple children.
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: Data> ViewSwitcher<T, U> {
/// Create a new view switcher.
///
/// The `child_picker` closure is called every time the application data changes.
/// If the value it returns is the same as the one it returned during the previous
/// data change, nothing happens. If it returns a different value, then the
/// `child_builder` closure is called with the new value.
///
/// The `child_builder` closure creates a new child widget based on
/// the value passed to it.
///
/// # Examples
/// ```
/// use druid::{
/// widget::{Label, ViewSwitcher},
/// Data, Widget,
/// };
///
/// #[derive(Clone, PartialEq, Data)]
/// enum Foo {
/// A,
/// B,
/// C,
/// }
///
/// fn ui() -> impl Widget<Foo> {
/// ViewSwitcher::new(
/// |data: &Foo, _env| data.clone(),
/// |selector, _data, _env| match selector {
/// Foo::A => Box::new(Label::new("A")),
/// _ => Box::new(Label::new("Not A")),
/// },
/// )
/// }
/// ```
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: Data> Widget<T> for ViewSwitcher<T, U> {
#[instrument(
name = "ViewSwitcher",
level = "trace",
skip(self, ctx, event, data, env)
)]
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);
}
}
#[instrument(
name = "ViewSwitcher",
level = "trace",
skip(self, 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);
}
}
#[instrument(
name = "ViewSwitcher",
level = "trace",
skip(self, ctx, _old_data, data, env)
)]
fn update(&mut self, ctx: &mut UpdateCtx, _old_data: &T, data: &T, env: &Env) {
let child_id = (self.child_picker)(data, env);
// Safe to unwrap because self.active_child_id should not be empty
if !child_id.same(self.active_child_id.as_ref().unwrap()) {
self.active_child = Some(WidgetPod::new((self.child_builder)(&child_id, data, env)));
self.active_child_id = Some(child_id);
ctx.children_changed();
// Because the new child has not yet been initialized, we have to skip the update after switching.
} else if let Some(child) = self.active_child.as_mut() {
child.update(ctx, data, env);
}
}
#[instrument(name = "ViewSwitcher", level = "trace", skip(self, ctx, bc, 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_origin(ctx, Point::ORIGIN);
size
}
None => bc.max(),
}
}
#[instrument(name = "ViewSwitcher", level = "trace", skip(self, ctx, data, env))]
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);
}
}
}