Struct gtk4::ConstantExpression

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#[repr(transparent)]
pub struct ConstantExpression { /* private fields */ }

Expand description

A constant value in a Expression.

Implementations

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impl ConstantExpression

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pub fn for_value(value: &Value) -> ConstantExpression

Creates an expression that always evaluates to the given value.

pub fn value(&self) -> Value

Gets the value that a constant expression evaluates to.

impl ConstantExpression

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pub fn new<V: ToValue>(value: &V) -> Self

Creates a Expression that evaluates to the object given by the arguments.

pub fn value_as<V: for<'b> FromValue<'b> + 'static>(&self) -> V

Similar to Self::value but panics if the value is of a different type.

Methods from Deref<Target = Expression>

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pub const NONE: Option<&'static Expression> = None

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pub fn bind(
 &self,
 target: &impl IsA<Object>,
 property: &str,
 this_: Option<&impl IsA<Object>>
) -> ExpressionWatch

Bind target’s property named property to self.

The value that self evaluates to is set via g_object_set() on target. This is repeated whenever self changes to ensure that the object’s property stays synchronized with self.

If self’s evaluation fails, target’s property is not updated. You can ensure that this doesn’t happen by using a fallback expression.

Note that this function takes ownership of self. If you want to keep it around, you should Gtk::Expression::ref() it beforehand.

`property`

name of the property on target to bind to

`this_`

the this argument for the evaluation of self

pub fn value_type(&self) -> Type

Gets the GType that this expression evaluates to.

This type is constant and will not change over the lifetime of this expression.

Returns

The type returned from evaluate()

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pub fn is_static(&self) -> bool

Checks if the expression is static.

A static expression will never change its result when evaluate() is called on it with the same arguments.

That means a call to watch() is not necessary because it will never trigger a notify.

Returns

TRUE if the expression is static

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pub fn watch<P: Fn() + 'static>(
 &self,
 this_: Option<&impl IsA<Object>>,
 notify: P
) -> ExpressionWatch

Watch the given expression for changes.

The @notify function will be called whenever the evaluation of self may have changed.

GTK cannot guarantee that the evaluation did indeed change when the @notify gets invoked, but it guarantees the opposite: When it did in fact change, the @notify will be invoked.

`notify`

callback to invoke when the expression changes

The newly installed watch. Note that the only reference held to the watch will be released when the watch is unwatched which can happen automatically, and not just via ExpressionWatch::unwatch(). You should call Gtk::ExpressionWatch::ref() if you want to keep the watch around.

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pub fn evaluate_as<V: for<'b> FromValue<'b> + 'static, T: IsA<Object>>(
&self,
this: Option<&T>
) -> Option<V>

Similar to Self::evaluate but panics if the value is of a different type.

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pub fn chain_property<T: IsA<Object>>(
&self,
property_name: &str
) -> PropertyExpression

Create a PropertyExpression that looks up for property_name with self as parameter. This is useful in long chains of Expressions.

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pub fn chain_closure<R>(&self, closure: RustClosure) -> ClosureExpression where
R: ValueType,

Create a ClosureExpression from a glib::Closure with self as the second parameter and R as the return type. The return type is checked at run-time and must always be specified. This is useful in long chains of Expressions when using the [glib::closure!] macro.

Note that the first parameter will always be the this object bound to the expression. If None is passed as this then the type of the first parameter must be Option<glib::Object> otherwise type checking will panic.

use gtk::prelude::*;
use gtk::glib;
use glib::{closure, Object};

let button = gtk::Button::new();
button.set_label("Hello");
let label = button
    .property_expression("label")
    .chain_closure::<String>(closure!(|_: Option<Object>, label: &str| {
        format!("{} World", label)
    }))
    .evaluate_as::<String, _>(gtk::Widget::NONE);
assert_eq!(label.unwrap(), "Hello World");