Struct gtk4::ConstraintLayout[−][src]

pub struct ConstraintLayout(_);

Expand description

A layout manager using constraints to describe relations between widgets.

ConstraintLayout is a layout manager that uses relations between widget attributes, expressed via Constraint instances, to measure and allocate widgets.

How do constraints work

Constraints are objects defining the relationship between attributes of a widget; you can read the description of the Constraint class to have a more in depth definition.

By taking multiple constraints and applying them to the children of a widget using ConstraintLayout, it’s possible to describe complex layout policies; each constraint applied to a child or to the parent widgets contributes to the full description of the layout, in terms of parameters for resolving the value of each attribute.

It is important to note that a layout is defined by the totality of constraints; removing a child, or a constraint, from an existing layout without changing the remaining constraints may result in an unstable or unsolvable layout.

Constraints have an implicit “reading order”; you should start describing each edge of each child, as well as their relationship with the parent container, from the top left (or top right, in RTL languages), horizontally first, and then vertically.

A constraint-based layout with too few constraints can become “unstable”, that is: have more than one solution. The behavior of an unstable layout is undefined.

A constraint-based layout with conflicting constraints may be unsolvable, and lead to an unstable layout. You can use the property::Constraint::strength property of Constraint to “nudge” the layout towards a solution.

GtkConstraintLayout as GtkBuildable

ConstraintLayout implements the Buildable interface and has a custom “constraints” element which allows describing constraints in a Builder UI file.

An example of a UI definition fragment specifying a constraint:

  <object class="GtkConstraintLayout">
    <constraints>
      <constraint target="button" target-attribute="start"
                  relation="eq"
                  source="super" source-attribute="start"
                  constant="12"
                  strength="required" />
      <constraint target="button" target-attribute="width"
                  relation="ge"
                  constant="250"
                  strength="strong" />
    </constraints>
  </object>

The definition above will add two constraints to the GtkConstraintLayout:

a required constraint between the leading edge of “button” and the leading edge of the widget using the constraint layout, plus 12 pixels
a strong, constant constraint making the width of “button” greater than, or equal to 250 pixels

The “target” and “target-attribute” attributes are required.

The “source” and “source-attribute” attributes of the “constraint” element are optional; if they are not specified, the constraint is assumed to be a constant.

The “relation” attribute is optional; if not specified, the constraint is assumed to be an equality.

The “strength” attribute is optional; if not specified, the constraint is assumed to be required.

The “source” and “target” attributes can be set to “super” to indicate that the constraint target is the widget using the GtkConstraintLayout.

There can be “constant” and “multiplier” attributes.

Additionally, the “constraints” element can also contain a description of the GtkConstraintGuides used by the layout:

  <constraints>
    <guide min-width="100" max-width="500" name="hspace"/>
    <guide min-height="64" nat-height="128" name="vspace" strength="strong"/>
  </constraints>

The “guide” element has the following optional attributes:

“min-width”, “nat-width”, and “max-width”, describe the minimum, natural, and maximum width of the guide, respectively
“min-height”, “nat-height”, and “max-height”, describe the minimum, natural, and maximum height of the guide, respectively
“strength” describes the strength of the constraint on the natural size of the guide; if not specified, the constraint is assumed to have a medium strength
“name” describes a name for the guide, useful when debugging

Using the Visual Format Language

Complex constraints can be described using a compact syntax called VFL, or Visual Format Language.

The Visual Format Language describes all the constraints on a row or column, typically starting from the leading edge towards the trailing one. Each element of the layout is composed by “views”, which identify a ConstraintTarget.

For instance:

  [button]-[textField]

Describes a constraint that binds the trailing edge of “button” to the leading edge of “textField”, leaving a default space between the two.

Using VFL is also possible to specify predicates that describe constraints on attributes like width and height:

  // Width must be greater than, or equal to 50
  [button(>=50)]

  // Width of button1 must be equal to width of button2
  [button1(==button2)]

The default orientation for a VFL description is horizontal, unless otherwise specified:

  // horizontal orientation, default attribute: width
  H:[button(>=150)]

  // vertical orientation, default attribute: height
  V:[button1(==button2)]

It’s also possible to specify multiple predicates, as well as their strength:

  // minimum width of button must be 150
  // natural width of button can be 250
  [button(>=150@required, ==250@medium)]

Finally, it’s also possible to use simple arithmetic operators:

  // width of button1 must be equal to width of button2
  // divided by 2 plus 12
  [button1(button2 / 2 + 12)]

Struct gtk4::ConstraintLayout[−][src]

Implementations

impl ConstraintLayout

pub fn new() -> ConstraintLayout

pub fn add_constraint(&self, constraint: &Constraint)

pub fn add_guide(&self, guide: &ConstraintGuide)

pub fn observe_constraints(&self) -> ListModel

pub fn observe_guides(&self) -> ListModel

pub fn remove_all_constraints(&self)

pub fn remove_constraint(&self, constraint: &Constraint)

pub fn remove_guide(&self, guide: &ConstraintGuide)

impl ConstraintLayout

pub fn add_constraints_from_description<W: IsA<Widget>>( &self, lines: &[&str], hspacing: i32, vspacing: i32, views: &HashMap<&str, &W>) -> Result<Vec<Constraint>, Error>

Trait Implementations

impl Clone for ConstraintLayout

fn clone(&self) -> ConstraintLayout

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

impl Debug for ConstraintLayout

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

impl Default for ConstraintLayout

fn default() -> Self

impl Display for ConstraintLayout

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

impl Hash for ConstraintLayout

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

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

impl Ord for ConstraintLayout

fn cmp(&self, other: &ConstraintLayout) -> Ordering

fn max(self, other: Self) -> Self

fn min(self, other: Self) -> Self

fn clamp(self, min: Self, max: Self) -> Self

impl ParentClassIs for ConstraintLayout

type Parent = LayoutManager

impl<T: ObjectType> PartialEq<T> for ConstraintLayout

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

fn ne(&self, other: &Rhs) -> bool

impl<T: ObjectType> PartialOrd<T> for ConstraintLayout

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

fn lt(&self, other: &Rhs) -> bool

fn le(&self, other: &Rhs) -> bool

fn gt(&self, other: &Rhs) -> bool

fn ge(&self, other: &Rhs) -> bool

impl StaticType for ConstraintLayout

fn static_type() -> Type

impl Eq for ConstraintLayout

impl IsA<Buildable> for ConstraintLayout

impl IsA<LayoutManager> for ConstraintLayout

impl StructuralEq for ConstraintLayout

Auto Trait Implementations

impl RefUnwindSafe for ConstraintLayout

impl !Send for ConstraintLayout

impl !Sync for ConstraintLayout

impl Unpin for ConstraintLayout

impl UnwindSafe for ConstraintLayout

Blanket Implementations

impl<T> Any for T where T: 'static + ?Sized,

pub fn type_id(&self) -> TypeId

impl<T> Borrow<T> for T where T: ?Sized,

pub fn borrow(&self) -> &T

impl<T> BorrowMut<T> for T where T: ?Sized,

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

impl<T> Cast for T where T: ObjectType,

fn upcast<T>(self) -> T where T: ObjectType, Self: IsA<T>,

fn upcast_ref<T>(&self) -> &T where T: ObjectType, Self: IsA<T>,

fn downcast<T>(self) -> Result<T, Self> where T: ObjectType, Self: CanDowncast<T>,

fn downcast_ref<T>(&self) -> Option<&T> where T: ObjectType, Self: CanDowncast<T>,

fn dynamic_cast<T>(self) -> Result<T, Self> where T: ObjectType,

fn dynamic_cast_ref<T>(&self) -> Option<&T> where T: ObjectType,

unsafe fn unsafe_cast<T>(self) -> T where T: ObjectType,

unsafe fn unsafe_cast_ref<T>(&self) -> &T where T: ObjectType,

impl<T> From<T> for T

pub fn from(t: T) -> T

impl<T, U> Into<U> for T where U: From<T>,

pub fn into(self) -> U

impl<T> ObjectExt for T where T: ObjectType,

pub fn is<U>(&self) -> bool where U: StaticType,

pub fn type_(&self) -> Type

pub fn object_class(&self) -> &Class<Object>

pub fn class(&self) -> &Class<T> where T: IsClass,

pub fn class_of<U>(&self) -> Option<&Class<U>> where U: IsClass,

pub fn add_constraints_from_description<W: IsA<Widget>>(
&self,
lines: &[&str ],
hspacing: i32,
vspacing: i32,
views: &HashMap<&str, &W>
) -> Result<Vec<Constraint>, Error>

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

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

impl<T> Any for T where
T: 'static + ?Sized,

impl<T> Borrow<T> for T where
T: ?Sized,

impl<T> BorrowMut<T> for T where
T: ?Sized,

impl<T> Cast for T where
T: ObjectType,

fn upcast<T>(self) -> T where
T: ObjectType,
Self: IsA<T>,

fn upcast_ref<T>(&self) -> &T where
T: ObjectType,
Self: IsA<T>,

fn downcast<T>(self) -> Result<T, Self> where
T: ObjectType,
Self: CanDowncast<T>,

fn downcast_ref<T>(&self) -> Option<&T> where
T: ObjectType,
Self: CanDowncast<T>,

fn dynamic_cast<T>(self) -> Result<T, Self> where
T: ObjectType,

fn dynamic_cast_ref<T>(&self) -> Option<&T> where
T: ObjectType,

unsafe fn unsafe_cast<T>(self) -> T where
T: ObjectType,

unsafe fn unsafe_cast_ref<T>(&self) -> &T where
T: ObjectType,

impl<T, U> Into<U> for T where
U: From<T>,

impl<T> ObjectExt for T where
T: ObjectType,

pub fn is<U>(&self) -> bool where
U: StaticType,

pub fn class(&self) -> &Class<T> where
T: IsClass,

pub fn class_of<U>(&self) -> Option<&Class<U>> where
U: IsClass,

pub fn interface<U>(&self) -> Option<InterfaceRef<'_, U>> where
U: IsInterface,

pub fn set_property<'a, N, V>(
&self,
property_name: N,
value: V
) -> Result<(), BoolError> where
N: Into<&'a str>,
V: ToValue,

pub fn set_property_from_value<'a, N>(
&self,
property_name: N,
value: &Value
) -> Result<(), BoolError> where
N: Into<&'a str>,

pub fn set_properties(
&self,
property_values: &[(&str, &dyn ToValue )]
) -> Result<(), BoolError>

pub fn set_properties_from_value(
&self,
property_values: &[(&str, Value )]
) -> Result<(), BoolError>

pub fn property<'a, N>(&self, property_name: N) -> Result<Value, BoolError> where
N: Into<&'a str>,

pub fn has_property<'a, N>(&self, property_name: N, type_: Option<Type>) -> bool where
N: Into<&'a str>,

pub fn property_type<'a, N>(&self, property_name: N) -> Option<Type> where
N: Into<&'a str>,

pub fn find_property<'a, N>(&self, property_name: N) -> Option<ParamSpec> where
N: Into<&'a str>,

pub unsafe fn set_qdata<QD>(&self, key: Quark, value: QD) where
QD: 'static,

pub unsafe fn qdata<QD>(&self, key: Quark) -> Option<NonNull<QD>> where
QD: 'static,

pub unsafe fn steal_qdata<QD>(&self, key: Quark) -> Option<QD> where
QD: 'static,

pub unsafe fn set_data<QD>(&self, key: &str, value: QD) where
QD: 'static,

pub unsafe fn data<QD>(&self, key: &str) -> Option<NonNull<QD>> where
QD: 'static,

pub unsafe fn steal_data<QD>(&self, key: &str) -> Option<QD> where
QD: 'static,

pub fn connect<'a, N, F>(
&self,
signal_name: N,
after: bool,
callback: F
) -> Result<SignalHandlerId, BoolError> where
N: Into<&'a str>,
F: 'static + Fn(&[Value ]) -> Option<Value> + Send + Sync,

pub fn connect_id<F>(
&self,
signal_id: SignalId,
details: Option<Quark>,
after: bool,
callback: F
) -> Result<SignalHandlerId, BoolError> where
F: 'static + Fn(&[Value ]) -> Option<Value> + Send + Sync,

pub fn connect_local<'a, N, F>(
&self,
signal_name: N,
after: bool,
callback: F
) -> Result<SignalHandlerId, BoolError> where
N: Into<&'a str>,
F: 'static + Fn(&[Value ]) -> Option<Value>,

pub fn connect_local_id<F>(
&self,
signal_id: SignalId,
details: Option<Quark>,
after: bool,
callback: F
) -> Result<SignalHandlerId, BoolError> where
F: 'static + Fn(&[Value ]) -> Option<Value>,

pub unsafe fn connect_unsafe<'a, N, F>(
&self,
signal_name: N,
after: bool,
callback: F
) -> Result<SignalHandlerId, BoolError> where
N: Into<&'a str>,
F: Fn(&[Value ]) -> Option<Value>,

pub unsafe fn connect_unsafe_id<F>(
&self,
signal_id: SignalId,
details: Option<Quark>,
after: bool,
callback: F
) -> Result<SignalHandlerId, BoolError> where
F: Fn(&[Value ]) -> Option<Value>,

pub fn emit(
&self,
signal_id: SignalId,
args: &[&dyn ToValue ]
) -> Result<Option<Value>, BoolError>

pub fn emit_with_values(
&self,
signal_id: SignalId,
args: &[Value ]
) -> Result<Option<Value>, BoolError>

pub fn emit_by_name<'a, N>(
&self,
signal_name: N,
args: &[&dyn ToValue ]
) -> Result<Option<Value>, BoolError> where
N: Into<&'a str>,

pub fn emit_by_name_with_values<'a, N>(
&self,
signal_name: N,
args: &[Value ]
) -> Result<Option<Value>, BoolError> where
N: Into<&'a str>,

pub fn emit_with_details(
&self,
signal_id: SignalId,
details: Quark,
args: &[&dyn ToValue ]
) -> Result<Option<Value>, BoolError>

pub fn emit_with_details_and_values(
&self,
signal_id: SignalId,
details: Quark,
args: &[Value ]
) -> Result<Option<Value>, BoolError>

pub fn connect_notify<F>(&self, name: Option<&str>, f: F) -> SignalHandlerId where
F: 'static + Fn(&T, &ParamSpec) + Send + Sync,

pub fn connect_notify_local<F>(
&self,
name: Option<&str>,
f: F
) -> SignalHandlerId where
F: 'static + Fn(&T, &ParamSpec),

pub unsafe fn connect_notify_unsafe<F>(
&self,
name: Option<&str>,
f: F
) -> SignalHandlerId where
F: Fn(&T, &ParamSpec),

pub fn notify<'a, N>(&self, property_name: N) where
N: Into<&'a str>,

pub fn bind_property<'a, O, N, M>(
&'a self,
source_property: N,
target: &'a O,
target_property: M
) -> BindingBuilder<'a> where
O: ObjectType,
N: Into<&'a str>,
M: Into<&'a str>,

impl<T> ToOwned for T where
T: Clone,

impl<T> ToSendValue for T where
T: Send + ToValue + ?Sized,

impl<T> ToString for T where
T: Display + ?Sized,