logo
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

// Copyright © SixtyFPS GmbH <info@slint-ui.com>
// SPDX-License-Identifier: GPL-3.0-only OR LicenseRef-Slint-commercial

/*!
Callback that can be connected to one single handler.

TODO: reconsider if we should rename that to `Event`
but then it should also be renamed everywhere, including in the language grammar
*/

#![warn(missing_docs)]

use alloc::boxed::Box;
use core::cell::Cell;

/// A Callback that can be connected to a handler.
///
/// The Arg represents the argument. It should always be a tuple
///
#[repr(C)]
pub struct Callback<Arg: ?Sized, Ret = ()> {
    /// FIXME: Box<dyn> is a fat object and we probably want to put an erased type in there
    handler: Cell<Option<Box<dyn FnMut(&Arg, &mut Ret)>>>,
}

impl<Arg: ?Sized, Ret> Default for Callback<Arg, Ret> {
    fn default() -> Self {
        Self { handler: Default::default() }
    }
}

impl<Arg: ?Sized, Ret: Default> Callback<Arg, Ret> {
    /// Call the callback with the given argument.
    pub fn call(&self, a: &Arg) -> Ret {
        let mut r = Ret::default();
        if let Some(mut h) = self.handler.take() {
            h(a, &mut r);
            assert!(self.handler.take().is_none(), "Callback Handler set while called");
            self.handler.set(Some(h));
        }
        r
    }

    /// Set an handler to be called when the callback is called
    ///
    /// There can only be one single handler per callback.
    pub fn set_handler(&self, mut f: impl FnMut(&Arg) -> Ret + 'static) {
        self.handler.set(Some(Box::new(move |a: &Arg, r: &mut Ret| *r = f(a))));
    }
}

#[test]
fn callback_simple_test() {
    use std::rc::Rc;
    #[derive(Default)]
    struct Component {
        pressed: core::cell::Cell<bool>,
        clicked: Callback<()>,
    }
    let c = Rc::new(Component::default());
    let weak = Rc::downgrade(&c);
    c.clicked.set_handler(move |()| weak.upgrade().unwrap().pressed.set(true));
    c.clicked.call(&());
    assert!(c.pressed.get());
}

#[cfg(feature = "ffi")]
pub(crate) mod ffi {
    #![allow(unsafe_code)]

    use super::*;

    #[allow(non_camel_case_types)]
    type c_void = ();
    #[repr(C)]
    /// Has the same layout as Callback<_>
    pub struct CallbackOpaque(*const c_void, *const c_void);

    static_assertions::assert_eq_align!(CallbackOpaque, Callback<()>);
    static_assertions::assert_eq_size!(CallbackOpaque, Callback<()>);
    static_assertions::assert_eq_align!(CallbackOpaque, Callback<(alloc::string::String,)>);
    static_assertions::assert_eq_size!(CallbackOpaque, Callback<(alloc::string::String,)>);

    /// Initialize the callback.
    /// slint_callback_drop must be called.
    #[no_mangle]
    pub unsafe extern "C" fn slint_callback_init(out: *mut CallbackOpaque) {
        assert_eq!(core::mem::size_of::<CallbackOpaque>(), core::mem::size_of::<Callback<()>>());
        core::ptr::write(out as *mut Callback<()>, Default::default());
    }

    /// Emit the callback
    #[no_mangle]
    pub unsafe extern "C" fn slint_callback_call(
        sig: *const CallbackOpaque,
        arg: *const c_void,
        ret: *mut c_void,
    ) {
        let sig = &*(sig as *const Callback<c_void>);
        if let Some(mut h) = sig.handler.take() {
            h(&*arg, &mut *ret);
            assert!(sig.handler.take().is_none(), "Callback Handler set while called");
            sig.handler.set(Some(h));
        }
    }

    /// Set callback handler.
    ///
    /// The binding has signature fn(user_data)
    #[no_mangle]
    pub unsafe extern "C" fn slint_callback_set_handler(
        sig: *const CallbackOpaque,
        binding: extern "C" fn(user_data: *mut c_void, arg: *const c_void, ret: *mut c_void),
        user_data: *mut c_void,
        drop_user_data: Option<extern "C" fn(*mut c_void)>,
    ) {
        let sig = &mut *(sig as *mut Callback<c_void>);

        struct UserData {
            user_data: *mut c_void,
            drop_user_data: Option<extern "C" fn(*mut c_void)>,
            binding: extern "C" fn(user_data: *mut c_void, arg: *const c_void, ret: *mut c_void),
        }

        impl Drop for UserData {
            fn drop(&mut self) {
                if let Some(x) = self.drop_user_data {
                    x(self.user_data)
                }
            }
        }

        impl UserData {
            /// Safety: the arguments must be valid pointers
            unsafe fn call(&self, arg: *const c_void, ret: *mut c_void) {
                (self.binding)(self.user_data, arg, ret)
            }
        }

        let ud = UserData { user_data, drop_user_data, binding };
        sig.handler.set(Some(Box::new(move |a: &(), r: &mut ()| {
            ud.call(a as *const c_void, r as *mut c_void)
        })));
    }

    /// Destroy callback
    #[no_mangle]
    pub unsafe extern "C" fn slint_callback_drop(handle: *mut CallbackOpaque) {
        core::ptr::drop_in_place(handle as *mut Callback<()>);
    }
}