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

// 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-controlling widget.

use crate::debug_state::DebugState;
use crate::widget::prelude::*;
use crate::widget::{Axis, WidgetWrapper};

/// A trait for types that modify behaviour of a child widget.
///
/// A `Controller` is a type that manages a child widget, overriding or
/// customizing its event handling or update behaviour.
///
/// A controller can only handle events and update; it cannot effect layout
/// or paint.
///
/// `Controller` is a convenience; anything it can do could also be done
/// by creating a custom [`Widget`] that owned a child. This is somewhat cumbersome,
/// however, especially when you only want to intercept or modify one or two events.
///
/// The methods on `Controller` are identical to the methods on [`Widget`],
/// except that they are also passed the controller's child. The controller
/// is responsible for **explicitly** forwarding calls on to the child as needed.
///
/// A `Controller` is used with a [`ControllerHost`], which manages the relationship
/// between it and its child; although in general you would use the
/// [`WidgetExt::controller`] method instead of instantiating a host directly.
///
/// # Examples
///
/// A [`TextBox`] that takes focus on launch:
///
/// ```
/// # use druid::widget::{Controller, TextBox};
/// # use druid::{Env, Event, EventCtx, Widget};
/// struct TakeFocus;
///
/// impl<T, W: Widget<T>> Controller<T, W> for TakeFocus {
///     fn event(&mut self, child: &mut W, ctx: &mut EventCtx, event: &Event, data: &mut T, env: &Env) {
///         if let Event::WindowConnected = event {
///             ctx.request_focus();
///         }
///         child.event(ctx, event, data, env)
///     }
/// }
/// ```
///
/// [`TextBox`]: super::TextBox
/// [`WidgetExt::controller`]: super::WidgetExt::controller
pub trait Controller<T, W: Widget<T>> {
    /// Analogous to [`Widget::event`].
    fn event(&mut self, child: &mut W, ctx: &mut EventCtx, event: &Event, data: &mut T, env: &Env) {
        child.event(ctx, event, data, env)
    }

    /// Analogous to [`Widget::lifecycle`].
    fn lifecycle(
        &mut self,
        child: &mut W,
        ctx: &mut LifeCycleCtx,
        event: &LifeCycle,
        data: &T,
        env: &Env,
    ) {
        child.lifecycle(ctx, event, data, env)
    }

    /// Analogous to [`Widget::update`].
    fn update(&mut self, child: &mut W, ctx: &mut UpdateCtx, old_data: &T, data: &T, env: &Env) {
        child.update(ctx, old_data, data, env)
    }
}

/// A [`Widget`] that manages a child and a [`Controller`].
pub struct ControllerHost<W, C> {
    widget: W,
    controller: C,
}

impl<W, C> ControllerHost<W, C> {
    /// Create a new `ControllerHost`.
    pub fn new(widget: W, controller: C) -> ControllerHost<W, C> {
        ControllerHost { widget, controller }
    }
}

impl<T, W: Widget<T>, C: Controller<T, W>> Widget<T> for ControllerHost<W, C> {
    fn event(&mut self, ctx: &mut EventCtx, event: &Event, data: &mut T, env: &Env) {
        self.controller
            .event(&mut self.widget, ctx, event, data, env)
    }

    fn lifecycle(&mut self, ctx: &mut LifeCycleCtx, event: &LifeCycle, data: &T, env: &Env) {
        self.controller
            .lifecycle(&mut self.widget, ctx, event, data, env)
    }

    fn update(&mut self, ctx: &mut UpdateCtx, old_data: &T, data: &T, env: &Env) {
        self.controller
            .update(&mut self.widget, ctx, old_data, data, env)
    }

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

    fn paint(&mut self, ctx: &mut PaintCtx, data: &T, env: &Env) {
        self.widget.paint(ctx, data, env)
    }

    fn id(&self) -> Option<WidgetId> {
        self.widget.id()
    }

    fn debug_state(&self, data: &T) -> DebugState {
        DebugState {
            display_name: self.short_type_name().to_string(),
            children: vec![self.widget.debug_state(data)],
            ..Default::default()
        }
    }

    fn compute_max_intrinsic(
        &mut self,
        axis: Axis,
        ctx: &mut LayoutCtx,
        bc: &BoxConstraints,
        data: &T,
        env: &Env,
    ) -> f64 {
        self.widget.compute_max_intrinsic(axis, ctx, bc, data, env)
    }
}

impl<W, C> WidgetWrapper for ControllerHost<W, C> {
    widget_wrapper_body!(W, widget);
}