Struct gtk4::ConstantExpression

pub struct ConstantExpression(_);

A constant value in a Expression.

Implementations

impl ConstantExpression

pub fn upcast(self) -> Expression

pub fn upcast_ref(&self) -> &Expression

impl ConstantExpression

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

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

value_type

The type of the object

Returns

a new Expression

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

Creates an expression that always evaluates to the given value.

value

a GValue

Returns

a new Expression

pub fn value(&self) -> Value

Gets the value that a constant expression evaluates to.

Returns

the value

Methods from Deref<Target = Expression>

pub fn downcast_ref<E: IsExpression>(&self) -> Option<&E>

pub fn type_(&self) -> Type

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()

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

pub fn bind<T: IsA<Object>, U: IsA<Object>>(
    &self,
    target: &T,
    property_name: &str,
    this: Option<&U>
) -> 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.

target

the target object to bind to

property

name of the property on target to bind to

this_

the this argument for the evaluation of self

Returns

a ExpressionWatch

pub fn evaluate<T: IsA<Object>>(&self, this: Option<&T>) -> Option<Value>

Evaluates the given expression and on success stores the result in value.

The GType of value will be the type given by value_type().

It is possible that expressions cannot be evaluated - for example when the expression references objects that have been destroyed or set to NULL. In that case value will remain empty and FALSE will be returned.

this_

the this argument for the evaluation

value

an empty GValue

Returns

TRUE if the expression could be evaluated

pub fn watch<T: IsA<Object>, F: Fn() + 'static>(
    &self,
    this: Option<&T>,
    notify: F
) -> 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.

this_

the this argument to watch

notify

callback to invoke when the expression changes

Returns

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.

Trait Implementations

impl AsRef<Expression> for ConstantExpression

fn as_ref(&self) -> &Expression

Performs the conversion.

impl Clone for ConstantExpression

fn clone(&self) -> ConstantExpression

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for ConstantExpression

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

Formats the value using the given formatter.

impl Deref for ConstantExpression

type Target = Expression

The resulting type after dereferencing.

fn deref(&self) -> &Self::Target

Dereferences the value.

impl<'a> FromValue<'a> for ConstantExpression

type Checker = GenericValueTypeOrNoneChecker<Self>

Value type checker.

unsafe fn from_value(value: &'a Value) -> Self

Get the contained value from a Value.

impl StaticType for ConstantExpression

fn static_type() -> Type

Returns the type identifier of Self.

impl ToValue for ConstantExpression

fn to_value(&self) -> Value

Convert a value to a Value.

fn value_type(&self) -> Type

Returns the type identifer of self.

impl ToValueOptional for ConstantExpression

fn to_value_optional(s: Option<&Self>) -> Value

Convert an Option to a Value.

impl ValueType for ConstantExpression

type Type = Self

Type to get the Type from.