1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303
use std::marker::PhantomData; use crate::widget::prelude::*; use crate::{Data, Lens, Point, WidgetPod}; /// A policy that controls how a [`Scope`] will interact with its surrounding /// application data. Specifically, how to create an initial State from the /// input, and how to synchronise the two using a [`ScopeTransfer`]. /// /// [`Scope`]: struct.Scope.html /// [`ScopeTransfer`]: trait.ScopeTransfer.html pub trait ScopePolicy { /// The type of data that comes in from the surrounding application or scope. type In: Data; /// The type of data that the `Scope` will maintain internally. /// This will usually be larger than the input data, and will embed the input data. type State: Data; /// The type of transfer that will be used to synchronise internal and application state type Transfer: ScopeTransfer<In = Self::In, State = Self::State>; /// Make a new state and transfer from the input. /// /// This consumes the policy, so non-cloneable items can make their way /// into the state this way. fn create(self, inner: &Self::In) -> (Self::State, Self::Transfer); } /// A `ScopeTransfer` knows how to synchronise input data with its counterpart /// within a [`Scope`]. /// /// It is separate from the policy mainly to allow easy use of lenses to do /// synchronisation, with a custom [`ScopePolicy`]. /// /// [`Scope`]: struct.Scope.html /// [`ScopePolicy`]: trait.ScopePolicy.html pub trait ScopeTransfer { /// The type of data that comes in from the surrounding application or scope. type In: Data; /// The type of data that the Scope will maintain internally. type State: Data; /// Replace the input we have within our State with a new one from outside fn read_input(&self, state: &mut Self::State, inner: &Self::In); /// Take the modifications we have made and write them back /// to our input. fn write_back_input(&self, state: &Self::State, inner: &mut Self::In); } /// A default implementation of [`ScopePolicy`] that takes a function and a transfer. /// /// [`ScopePolicy`]: trait.ScopePolicy.html pub struct DefaultScopePolicy<F: FnOnce(Transfer::In) -> Transfer::State, Transfer: ScopeTransfer> { make_state: F, transfer: Transfer, } impl<F: FnOnce(Transfer::In) -> Transfer::State, Transfer: ScopeTransfer> DefaultScopePolicy<F, Transfer> { /// Create a `ScopePolicy` from a factory function and a `ScopeTransfer`. pub fn new(make_state: F, transfer: Transfer) -> Self { DefaultScopePolicy { make_state, transfer, } } } impl<F: FnOnce(In) -> State, L: Lens<State, In>, In: Data, State: Data> DefaultScopePolicy<F, LensScopeTransfer<L, In, State>> { /// Create a `ScopePolicy` from a factory function and a lens onto that /// `Scope`'s state. pub fn from_lens(make_state: F, lens: L) -> Self { Self::new(make_state, LensScopeTransfer::new(lens)) } } impl<F: Fn(Transfer::In) -> Transfer::State, Transfer: ScopeTransfer> ScopePolicy for DefaultScopePolicy<F, Transfer> { type In = Transfer::In; type State = Transfer::State; type Transfer = Transfer; fn create(self, inner: &Self::In) -> (Self::State, Self::Transfer) { let state = (self.make_state)(inner.clone()); (state, self.transfer) } } /// A `ScopeTransfer` that uses a Lens to synchronise between a large internal /// state and a small input. pub struct LensScopeTransfer<L: Lens<State, In>, In, State> { lens: L, phantom_in: PhantomData<In>, phantom_state: PhantomData<State>, } impl<L: Lens<State, In>, In, State> LensScopeTransfer<L, In, State> { /// Create a `ScopeTransfer` from a Lens onto a portion of the `Scope`'s state. pub fn new(lens: L) -> Self { LensScopeTransfer { lens, phantom_in: PhantomData::default(), phantom_state: PhantomData::default(), } } } impl<L: Lens<State, In>, In: Data, State: Data> ScopeTransfer for LensScopeTransfer<L, In, State> { type In = In; type State = State; fn read_input(&self, state: &mut State, data: &In) { self.lens.with_mut(state, |inner| { if !inner.same(&data) { *inner = data.clone() } }); } fn write_back_input(&self, state: &State, data: &mut In) { self.lens.with(state, |inner| { if !inner.same(&data) { *data = inner.clone(); } }); } } enum ScopeContent<SP: ScopePolicy> { Policy { policy: Option<SP>, }, Transfer { state: SP::State, transfer: SP::Transfer, }, } /// A widget that allows encapsulation of application state. /// /// This is useful in circumstances where /// * A (potentially reusable) widget is composed of a tree of multiple cooperating child widgets /// * Those widgets communicate amongst themselves using Druid's reactive data mechanisms /// * It is undesirable to complicate the surrounding application state with the internal details /// of the widget. /// /// /// Examples include: /// * In a tabs widget composed of a tab bar, and a widget switching body, those widgets need to /// cooperate on which tab is selected. However not every user of a tabs widget wishes to /// encumber their application state with this internal detail - especially as many tabs widgets may /// reasonably exist in an involved application. /// * In a table/grid widget composed of various internal widgets, many things need to be synchronised. /// Scroll position, heading moves, drag operations, sort/filter operations. For many applications /// access to this internal data outside of the table widget isn't needed. /// For this reason it may be useful to use a Scope to establish private state. /// /// A scope embeds some input state (from its surrounding application or parent scope) /// into a larger piece of internal state. This is controlled by a user provided policy. /// /// The ScopePolicy needs to do two things /// a) Create a new scope from the initial value of its input, /// b) Provide two way synchronisation between the input and the state via a ScopeTransfer /// /// Convenience methods are provided to make a policy from a function and a lens. /// It may sometimes be advisable to implement ScopePolicy directly if you need to /// mention the type of a Scope. /// /// # Examples /// ``` /// use druid::{Data, Lens, WidgetExt}; /// use druid::widget::{TextBox, Scope}; /// #[derive(Clone, Data, Lens)] /// struct AppState { /// name: String, /// } /// /// #[derive(Clone, Data, Lens)] /// struct PrivateState { /// text: String, /// other: u32, /// } /// /// impl PrivateState { /// pub fn new(text: String) -> Self { /// PrivateState { text, other: 0 } /// } /// } /// /// fn main() { /// let scope = Scope::from_lens( /// PrivateState::new, /// PrivateState::text, /// TextBox::new().lens(PrivateState::text), /// ); /// } /// ``` pub struct Scope<SP: ScopePolicy, W: Widget<SP::State>> { content: ScopeContent<SP>, inner: WidgetPod<SP::State, W>, } impl<SP: ScopePolicy, W: Widget<SP::State>> Scope<SP, W> { /// Create a new scope from a policy and an inner widget pub fn new(policy: SP, inner: W) -> Self { Scope { content: ScopeContent::Policy { policy: Some(policy), }, inner: WidgetPod::new(inner), } } fn with_state<V>( &mut self, data: &SP::In, mut f: impl FnMut(&mut SP::State, &mut WidgetPod<SP::State, W>) -> V, ) -> V { match &mut self.content { ScopeContent::Policy { policy } => { // We know that the policy is a Some - it is an option to allow // us to take ownership before replacing the content. let (mut state, policy) = policy.take().unwrap().create(data); let v = f(&mut state, &mut self.inner); self.content = ScopeContent::Transfer { state, transfer: policy, }; v } ScopeContent::Transfer { ref mut state, transfer, } => { transfer.read_input(state, data); f(state, &mut self.inner) } } } fn write_back_input(&mut self, data: &mut SP::In) { if let ScopeContent::Transfer { state, transfer } = &mut self.content { transfer.write_back_input(state, data) } } } impl< F: Fn(Transfer::In) -> Transfer::State, Transfer: ScopeTransfer, W: Widget<Transfer::State>, > Scope<DefaultScopePolicy<F, Transfer>, W> { /// Create a new policy from a function creating the state, and a ScopeTransfer synchronising it pub fn from_function(make_state: F, transfer: Transfer, inner: W) -> Self { Self::new(DefaultScopePolicy::new(make_state, transfer), inner) } } impl<In: Data, State: Data, F: Fn(In) -> State, L: Lens<State, In>, W: Widget<State>> Scope<DefaultScopePolicy<F, LensScopeTransfer<L, In, State>>, W> { /// Create a new policy from a function creating the state, and a Lens synchronising it pub fn from_lens(make_state: F, lens: L, inner: W) -> Self { Self::new(DefaultScopePolicy::from_lens(make_state, lens), inner) } } impl<SP: ScopePolicy, W: Widget<SP::State>> Widget<SP::In> for Scope<SP, W> { fn event(&mut self, ctx: &mut EventCtx, event: &Event, data: &mut SP::In, env: &Env) { self.with_state(data, |state, inner| inner.event(ctx, event, state, env)); self.write_back_input(data); ctx.request_update() } fn lifecycle(&mut self, ctx: &mut LifeCycleCtx, event: &LifeCycle, data: &SP::In, env: &Env) { self.with_state(data, |state, inner| inner.lifecycle(ctx, event, state, env)); } fn update(&mut self, ctx: &mut UpdateCtx, _old_data: &SP::In, data: &SP::In, env: &Env) { self.with_state(data, |state, inner| inner.update(ctx, state, env)); } fn layout( &mut self, ctx: &mut LayoutCtx, bc: &BoxConstraints, data: &SP::In, env: &Env, ) -> Size { self.with_state(data, |state, inner| { let size = inner.layout(ctx, bc, state, env); inner.set_origin(ctx, state, env, Point::ORIGIN); size }) } fn paint(&mut self, ctx: &mut PaintCtx, data: &SP::In, env: &Env) { self.with_state(data, |state, inner| inner.paint_raw(ctx, state, env)); } }