Struct azul_core::callbacks::Ref

pub struct Ref<T: 'static>(_);

The two-way binding system

A fundamental problem in UI development is where and how to store states of widgets, without impacting reusability, extensability or performance. Azul solves this problem using a type-erased Rc<RefCell<Box<Any>>> type (RefAny), whic can be up and downcasted to a Rc<RefCell<Box<T>>> type (Ref<T>). Ref and RefAny exist mostly to reduce typing and to prevent multiple mutable access to the inner RefCell at compile time. Azul stores all RefAnys inside the Dom tree and does NOT clone or mutate them at all. Only user-defined callbacks or the default callbacks have access to the RefAny data.

Overriding the default behaviour of widgets

While Rust does not support inheritance with language constructs such as @override (Java) or the override keyword in C#, emulating structs that can change their behaviour at runtime is quite easy. Imagine a struct in which all methods are stored as public function pointers inside the struct itself:

// The struct has all methods as function pointers,
// so that they can be "overridden" and exchanged with other
// implementations if necessary
struct A {
    pub function_a: fn(&A, i32) -> i32,
    pub function_b: fn(&A) -> &'static str,
}

impl A {
    pub fn default_impl_a(&self, num: i32) -> i32 { num + num }
    pub fn default_impl_b(&self) -> &'static str { "default b method!" }

    // Don't call default_impl_a() directly, just the function pointer
    pub fn do_a(&self, num: i32) -> i32 { (self.function_a)(self, num) }
    pub fn do_b(&self) -> &'static str { (self.function_b)(self) }
}

// Here we provide the default ("base class") implementation
impl Default for A {
    fn default() -> A {
        A {
            function_a: A::default_impl_a,
            function_b: A::default_impl_b,
        }
    }
}

// Alternative function that will override the original method
fn override_a(_: &A, num: i32) -> i32 { num * num }

fn main() {
    let mut a = A::default();
    println!("{}", a.do_a(5)); // prints "10" (5 + 5)
    println!("{}", a.do_b());  // prints "default b method"

    a.function_a = override_a; // Here we override the behaviour
    println!("{}", a.do_a(5)); // prints "25" (5 * 5)
    println!("{}", a.do_b());  // still prints "default b method", since method isn't overridden
}

Applied to widgets, the "A" class (a placeholder for a "Button", "Table" or other widget) can look something like this:

fn layout(&self, _: &LayoutInfo) -> Dom {
    Spreadsheet::new()
        .override_oncellchange(my_func_1)
        .override_onworkspacechange(my_func_2)
        .override_oncellselect(my_func_3)
    .dom()
}

The spreadsheet has some "default" event handlers, which can be exchanged for custom implementations via an open API. The benefit is that functions can be mixed and matched, and widgets can be composed of sub-widgets as well as be re-used. Another benefit is that now the widget can react to "custom" events such as "oncellchange" or "oncellselect", without Azul knowing that such events even exist. The downside is that this coding style requires more work on behalf of the widget designer (but not the user).

Implementations

impl<T: 'static> Ref<T>

pub fn new(data: T) -> Self

pub fn borrow(&self) -> StdRef<T>

pub fn borrow_mut(&mut self) -> StdRefMut<T>

pub fn get_type_name(&self) -> &'static str

pub fn upcast(self) -> RefAny

Trait Implementations

impl<T: 'static> Clone for Ref<T>

fn clone(&self) -> Self

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T: Debug + 'static> Debug for Ref<T>

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.

impl<T: Default + 'static> Default for Ref<T>

fn default() -> Ref<T>

Returns the "default value" for a type.

impl<T: Eq + 'static> Eq for Ref<T>

impl<T: 'static> From<Ref<T>> for RefAny

fn from(r: Ref<T>) -> Self

Performs the conversion.

impl<T: 'static + Hash> Hash for Ref<T>

fn hash<H>(&self, state: &mut H) where
    H: Hasher, 

Feeds this value into the given [Hasher].

fn hash_slice<H>(data: &[Self], state: &mut H) where
    H: Hasher, 

Feeds a slice of this type into the given [Hasher].

impl<T: Ord + 'static> Ord for Ref<T>

fn cmp(&self, other: &Ref<T>) -> Ordering

This method returns an [Ordering] between self and other.

#[must_use]fn max(self, other: Self) -> Self

Compares and returns the maximum of two values.

#[must_use]fn min(self, other: Self) -> Self

Compares and returns the minimum of two values.

#[must_use]fn clamp(self, min: Self, max: Self) -> Self

🔬 This is a nightly-only experimental API. (clamp)

Restrict a value to a certain interval.

impl<T: PartialEq + 'static> PartialEq<Ref<T>> for Ref<T>

fn eq(&self, other: &Ref<T>) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Ref<T>) -> bool

This method tests for !=.

impl<T: PartialOrd + 'static> PartialOrd<Ref<T>> for Ref<T>

fn partial_cmp(&self, other: &Ref<T>) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Ref<T>) -> bool

This method tests less than (for self and other) and is used by the < operator.

fn le(&self, other: &Ref<T>) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator.

fn gt(&self, other: &Ref<T>) -> bool

This method tests greater than (for self and other) and is used by the > operator.

fn ge(&self, other: &Ref<T>) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator.

impl<T: 'static> StructuralEq for Ref<T>

impl<T: 'static> StructuralPartialEq for Ref<T>