Package ch.bailu.gtk.gtk

Class ConstraintLayout

java.lang.Object
ch.bailu.gtk.type.Type
ch.bailu.gtk.type.Pointer
ch.bailu.gtk.gobject.Object
ch.bailu.gtk.gtk.LayoutManager
ch.bailu.gtk.gtk.ConstraintLayout
All Implemented Interfaces:
PointerInterface
public class ConstraintLayout extends LayoutManager
A layout manager using constraints to describe relations between widgets.

`GtkConstraintLayout` is a layout manager that uses relations between
widget attributes, expressed via [class@Gtk.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 [class@Gtk.Constraint]
class to have a more in depth definition.

By taking multiple constraints and applying them to the children of
a widget using `GtkConstraintLayout`, 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@Gtk.Constraint:strength]
property of [class@Gtk.Constraint] to "nudge" the layout towards a solution.

### GtkConstraintLayout as GtkBuildable

`GtkConstraintLayout` implements the [iface@Gtk.Buildable] interface and
has a custom "constraints" element which allows describing constraints in
a [class@Gtk.Builder] UI file.

An example of a UI definition fragment specifying a constraint:

```xml
<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:

```xml
<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 [iface@Gtk.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)]
```

https://docs.gtk.org/gtk4/class.ConstraintLayout.html

  • Constructor Details

    • ConstraintLayout

      public ConstraintLayout(PointerContainer pointer)

    • ConstraintLayout

      public ConstraintLayout()
      Creates a new `GtkConstraintLayout` layout manager.

  • Method Details

    • getClassHandler

      public static ClassHandler getClassHandler()

    • addConstraint

      public void addConstraint(@Nonnull Constraint constraint)
      Adds a constraint to the layout manager.

      The [property@Gtk.Constraint:source] and [property@Gtk.Constraint:target]
      properties of `constraint` can be:

      - set to `NULL` to indicate that the constraint refers to the
      widget using `layout`
      - set to the [class@Gtk.Widget] using `layout`
      - set to a child of the [class@Gtk.Widget] using `layout`
      - set to a [class@Gtk.ConstraintGuide] that is part of `layout`

      The @layout acquires the ownership of @constraint after calling
      this function.
      Parameters:
      constraint - a [class@Gtk.Constraint]

    • addConstraintsFromDescriptionv

      public List addConstraintsFromDescriptionv(@Nonnull Strs lines, long n_lines, int hspacing, int vspacing, @Nonnull HashTable views) throws AllocationError
      Creates a list of constraints from a VFL description.

      The Visual Format Language, VFL, is based on Apple's AutoLayout [VFL](https://developer.apple.com/library/content/documentation/UserExperience/Conceptual/AutolayoutPG/VisualFormatLanguage.html).

      The `views` dictionary is used to match [iface@Gtk.ConstraintTarget]
      instances to the symbolic view name inside the VFL.

      The VFL grammar is:

      ```
      <visualFormatString> = (<orientation>)?
      (<superview><connection>)?
      <view>(<connection><view>)*
      (<connection><superview>)?
      <orientation> = 'H' | 'V'
      <superview> = '|'
      <connection> = '' | '-' <predicateList> '-' | '-'
      <predicateList> = <simplePredicate> | <predicateListWithParens>
      <simplePredicate> = <metricName> | <positiveNumber>
      <predicateListWithParens> = '(' <predicate> (',' <predicate>)* ')'
      <predicate> = (<relation>)? <objectOfPredicate> (<operatorList>)? ('@' <priority>)?
      <relation> = '==' | '<=' | '>='
      <objectOfPredicate> = <constant> | <viewName> | ('.' <attributeName>)?
      <priority> = <positiveNumber> | 'required' | 'strong' | 'medium' | 'weak'
      <constant> = <number>
      <operatorList> = (<multiplyOperator>)? (<addOperator>)?
      <multiplyOperator> = [ '*' | '/' ] <positiveNumber>
      <addOperator> = [ '+' | '-' ] <positiveNumber>
      <viewName> = [A-Za-z_]([A-Za-z0-9_]*) // A C identifier
      <metricName> = [A-Za-z_]([A-Za-z0-9_]*) // A C identifier
      <attributeName> = 'top' | 'bottom' | 'left' | 'right' | 'width' | 'height' |
      'start' | 'end' | 'centerX' | 'centerY' | 'baseline'
      <positiveNumber> // A positive real number parseable by g_ascii_strtod()
      <number> // A real number parseable by g_ascii_strtod()
      ```

      **Note**: The VFL grammar used by GTK is slightly different than the one
      defined by Apple, as it can use symbolic values for the constraint's
      strength instead of numeric values; additionally, GTK allows adding
      simple arithmetic operations inside predicates.

      Examples of VFL descriptions are:

      ```
      // Default spacing
      [button]-[textField]

      // Width constraint
      [button(>=50)]

      // Connection to super view
      |-50-[purpleBox]-50-|

      // Vertical layout
      V:[topField]-10-[bottomField]

      // Flush views
      [maroonView][blueView]

      // Priority
      [button(100@strong)]

      // Equal widths
      [button1(==button2)]

      // Multiple predicates
      [flexibleButton(>=70,<=100)]

      // A complete line of layout
      |-[find]-[findNext]-[findField(>=20)]-|

      // Operators
      [button1(button2 / 3 + 50)]

      // Named attributes
      [button1(==button2.height)]
      ```
      Parameters:
      lines - an array of Visual Format Language lines defining a set of constraints
      n_lines - the number of lines
      hspacing - default horizontal spacing value, or -1 for the fallback value
      vspacing - default vertical spacing value, or -1 for the fallback value
      views - a dictionary of `[ name, target ]` pairs; the `name` keys map to the view names in the VFL lines, while the `target` values map to children of the widget using a `GtkConstraintLayout`, or guides
      Returns:
      the list of [class@Gtk.Constraint] instances that were added to the layout
      Throws:
      AllocationError

    • addGuide

      public void addGuide(@Nonnull ConstraintGuide guide)
      Adds a guide to `layout`.

      A guide can be used as the source or target of constraints,
      like a widget, but it is not visible.

      The `layout` acquires the ownership of `guide` after calling
      this function.
      Parameters:
      guide - a [class@Gtk.ConstraintGuide] object

    • observeConstraints

      public ListModel observeConstraints()
      Returns a `GListModel` to track the constraints that are
      part of the layout.

      Calling this function will enable extra internal bookkeeping
      to track constraints and emit signals on the returned listmodel.
      It may slow down operations a lot.

      Applications should try hard to avoid calling this function
      because of the slowdowns.
      Returns:
      a `GListModel` tracking the layout's constraints

    • observeGuides

      public ListModel observeGuides()
      Returns a `GListModel` to track the guides that are
      part of the layout.

      Calling this function will enable extra internal bookkeeping
      to track guides and emit signals on the returned listmodel.
      It may slow down operations a lot.

      Applications should try hard to avoid calling this function
      because of the slowdowns.
      Returns:
      a `GListModel` tracking the layout's guides

    • removeAllConstraints

      public void removeAllConstraints()
      Removes all constraints from the layout manager.

    • removeConstraint

      public void removeConstraint(@Nonnull Constraint constraint)
      Removes `constraint` from the layout manager,
      so that it no longer influences the layout.
      Parameters:
      constraint - a [class@Gtk.Constraint]

    • removeGuide

      public void removeGuide(@Nonnull ConstraintGuide guide)
      Removes `guide` from the layout manager,
      so that it no longer influences the layout.
      Parameters:
      guide - a [class@Gtk.ConstraintGuide] object

    • asBuildable

      public Buildable asBuildable()
      Implements interface Buildable. Call this to get access to interface functions.
      Returns:
      Buildable

    • getTypeID

      public static long getTypeID()

    • getParentTypeID

      public static long getParentTypeID()

    • getTypeSize

      public static TypeSystem.TypeSize getTypeSize()

    • getParentTypeSize

      public static TypeSystem.TypeSize getParentTypeSize()

    • getInstanceSize

      public static int getInstanceSize()