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// Copyright 2018 The xi-editor 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. use std::num::NonZeroU64; use std::ops::{Deref, DerefMut}; use super::prelude::*; /// A unique identifier for a single [`Widget`]. /// /// `WidgetId`s are generated automatically for all widgets that participate /// in layout. More specifically, each [`WidgetPod`] has a unique `WidgetId`. /// /// These ids are used internally to route events, and can be used to communicate /// between widgets, by submitting a command (as with [`EventCtx::submit_command`]) /// and passing a `WidgetId` as the [`Target`]. /// /// A widget can retrieve its id via methods on the various contexts, such as /// [`LifeCycleCtx::widget_id`]. /// /// ## Explicit `WidgetId`s. /// /// Sometimes, you may want to know a widget's id when constructing the widget. /// You can give a widget an _explicit_ id by wrapping it in an [`IdentityWrapper`] /// widget, or by using the [`WidgetExt::with_id`] convenience method. /// /// If you set a `WidgetId` directly, you are resposible for ensuring that it /// is unique in time. That is: only one widget can exist with a given id at a /// given time. /// /// [`Widget`]: trait.Widget.html /// [`EventCtx::submit_command`]: struct.EventCtx.html#method.submit_command /// [`Target`]: enum.Target.html /// [`WidgetPod`]: struct.WidgetPod.html /// [`LifeCycleCtx::widget_id`]: struct.LifeCycleCtx.html#method.widget_id /// [`WidgetExt::with_id`]: trait.WidgetExt.html#method.with_id /// [`IdentityWrapper`]: widget/struct.IdentityWrapper.html // this is NonZeroU64 because we regularly store Option<WidgetId> #[derive(Clone, Copy, Debug, Hash, PartialEq, Eq)] pub struct WidgetId(NonZeroU64); /// The trait implemented by all widgets. /// /// All appearance and behavior for a widget is encapsulated in an /// object that implements this trait. /// /// The trait is parametrized by a type (`T`) for associated data. /// All trait methods are provided with access to this data, and /// in the case of [`event`] the reference is mutable, so that events /// can directly update the data. /// /// Whenever the application data changes, the framework traverses /// the widget hierarchy with an [`update`] method. The framework /// needs to know whether the data has actually changed or not, which /// is why `T` has a [`Data`] bound. /// /// All the trait methods are provided with a corresponding context. /// The widget can request things and cause actions by calling methods /// on that context. /// /// In addition, all trait methods are provided with an environment /// ([`Env`]). /// /// Container widgets will generally not call `Widget` methods directly /// on their child widgets, but rather will own their widget wrapped in /// a [`WidgetPod`], and call the corresponding method on that. The /// `WidgetPod` contains state and logic for these traversals. On the /// other hand, particularly light-weight containers might contain their /// child `Widget` directly (when no layout or event flow logic is /// needed), and in those cases will call these methods. /// /// As a general pattern, container widgets will call the corresponding /// `WidgetPod` method on all their children. The `WidgetPod` applies /// logic to determine whether to recurse, as needed. /// /// [`event`]: #tymethod.event /// [`update`]: #tymethod.update /// [`Data`]: trait.Data.html /// [`Env`]: struct.Env.html /// [`WidgetPod`]: struct.WidgetPod.html pub trait Widget<T> { /// Handle an event. /// /// A number of different events (in the [`Event`] enum) are handled in this /// method call. A widget can handle these events in a number of ways: /// requesting things from the [`EventCtx`], mutating the data, or submitting /// a [`Command`]. /// /// [`Event`]: enum.Event.html /// [`EventCtx`]: struct.EventCtx.html /// [`Command`]: struct.Command.html fn event(&mut self, ctx: &mut EventCtx, event: &Event, data: &mut T, env: &Env); /// Handle a life cycle notification. /// /// This method is called to notify your widget of certain special events, /// (available in the [`LifeCycle`] enum) that are generally related to /// changes in the widget graph or in the state of your specific widget. /// /// A widget is not expected to mutate the application state in response /// to these events, but only to update its own internal state as required; /// if a widget needs to mutate data, it can submit a [`Command`] that will /// be executed at the next opportunity. /// /// [`LifeCycle`]: enum.LifeCycle.html /// [`LifeCycleCtx`]: struct.LifeCycleCtx.html /// [`Command`]: struct.Command.html fn lifecycle(&mut self, ctx: &mut LifeCycleCtx, event: &LifeCycle, data: &T, env: &Env); /// Handle a change of data. /// /// This method is called whenever the data changes. When the appearance of /// the widget depends on data, call [`request_paint`] so that it's scheduled /// for repaint. /// /// The previous value of the data is provided in case the widget wants to /// compute a fine-grained delta. /// /// [`request_paint`]: struct.UpdateCtx.html#method.request_paint fn update(&mut self, ctx: &mut UpdateCtx, old_data: &T, data: &T, env: &Env); /// Compute layout. /// /// A leaf widget should determine its size (subject to the provided /// constraints) and return it. /// /// A container widget will recursively call [`WidgetPod::layout`] on its /// child widgets, providing each of them an appropriate box constraint, /// compute layout, then call [`set_layout_rect`] on each of its children. /// Finally, it should return the size of the container. The container /// can recurse in any order, which can be helpful to, for example, compute /// the size of non-flex widgets first, to determine the amount of space /// available for the flex widgets. /// /// For efficiency, a container should only invoke layout of a child widget /// once, though there is nothing enforcing this. /// /// The layout strategy is strongly inspired by Flutter. /// /// [`WidgetPod::layout`]: struct.WidgetPod.html#method.layout /// [`set_layout_rect`]: struct.WidgetPod.html#method.set_layout_rect fn layout(&mut self, ctx: &mut LayoutCtx, bc: &BoxConstraints, data: &T, env: &Env) -> Size; /// Paint the widget appearance. /// /// The [`PaintCtx`] derefs to something that implements the [`RenderContext`] /// trait, which exposes various methods that the widget can use to paint /// its appearance. /// /// Container widgets can paint a background before recursing to their /// children, or annotations (for example, scrollbars) by painting /// afterwards. In addition, they can apply masks and transforms on /// the render context, which is especially useful for scrolling. /// /// [`PaintCtx`]: struct.PaintCtx.html /// [`RenderContext`]: trait.RenderContext.html fn paint(&mut self, ctx: &mut PaintCtx, data: &T, env: &Env); #[doc(hidden)] /// Get the identity of the widget; this is basically only implemented by /// `IdentityWrapper`. Widgets should not implement this on their own. fn id(&self) -> Option<WidgetId> { None } #[doc(hidden)] /// Get the (verbose) type name of the widget for debugging purposes. /// You should not override this method. fn type_name(&self) -> &'static str { std::any::type_name::<Self>() } } impl WidgetId { /// Allocate a new, unique `WidgetId`. /// /// All widgets are assigned ids automatically; you should only create /// an explicit id if you need to know it ahead of time, for instance /// if you want two sibling widgets to know each others' ids. /// /// You must ensure that a given `WidgetId` is only ever used for one /// widget at a time. pub fn next() -> WidgetId { use crate::shell::Counter; static WIDGET_ID_COUNTER: Counter = Counter::new(); WidgetId(WIDGET_ID_COUNTER.next_nonzero()) } /// Create a reserved `WidgetId`, suitable for reuse. /// /// The caller is responsible for ensuring that this ID is in fact assigned /// to a single widget at any time, or your code may become haunted. /// /// The actual inner representation of the returned `WidgetId` will not /// be the same as the raw value that is passed in; it will be /// `u64::max_value() - raw`. #[allow(unsafe_code)] pub const fn reserved(raw: u16) -> WidgetId { let id = u64::max_value() - raw as u64; // safety: by construction this can never be zero. WidgetId(unsafe { std::num::NonZeroU64::new_unchecked(id) }) } pub(crate) fn to_raw(self) -> u64 { self.0.into() } } impl<T> Widget<T> for Box<dyn Widget<T>> { fn event(&mut self, ctx: &mut EventCtx, event: &Event, data: &mut T, env: &Env) { self.deref_mut().event(ctx, event, data, env) } fn lifecycle(&mut self, ctx: &mut LifeCycleCtx, event: &LifeCycle, data: &T, env: &Env) { self.deref_mut().lifecycle(ctx, event, data, env); } fn update(&mut self, ctx: &mut UpdateCtx, old_data: &T, data: &T, env: &Env) { self.deref_mut().update(ctx, old_data, data, env); } fn layout(&mut self, ctx: &mut LayoutCtx, bc: &BoxConstraints, data: &T, env: &Env) -> Size { self.deref_mut().layout(ctx, bc, data, env) } fn paint(&mut self, ctx: &mut PaintCtx, data: &T, env: &Env) { self.deref_mut().paint(ctx, data, env); } fn id(&self) -> Option<WidgetId> { self.deref().id() } fn type_name(&self) -> &'static str { self.deref().type_name() } }