Class “Constraint”
Represents a constraint on the layout of a widget that the parent uses to determine the position of one of its edges. See also ConstraintValue
| Type: | Constraint extends Object |
| Constructor: | public |
| Singleton: | No |
| Namespace: | tabris |
| Direct subclasses: | None |
| JSX Support: | No |
Constructor
new Constraint(reference, offset)
| Parameter | Type | Description |
|---|---|---|
| reference | Percent | SiblingReference |
Sets the reference property. |
| offset | Offset |
Sets the offset property. |
Methods
equals(value)
Tests if the given value is a Constraint instance that is deeply equal to this one.
| Parameter | Type | Description |
|---|---|---|
| value | Constraint |
Returns: boolean
toArray()
A tuple consisting of the values of the reference and offset properties, i.e. [reference, offset].
Returns: ConstraintArray
toString()
A string representation of the constraint as a space separated string in the pattern of 'reference offset'.
Returns: string
Static Methods
from(constraintValue)
Creates a new instance of Constraint using any valid constraint expression. For any other value, including null and 'auto', the method throws.
| Parameter | Type | Description |
|---|---|---|
| constraintValue | ConstraintValue |
The value to create an Constraint instance from. |
Returns: Constraint
Properties
offset
An additional distance between the reference point and the edge of the widget itself.
| Type: | Offset |
| Settable: | Yes |
This property can only be set via constructor. Once set, it cannot change anymore.
reference
A reference point from which the offset is added. Either a SiblingReference - indicating the opposing edge of that widget - or a Percent instance, indicating a fraction of the width/height (padding excluded) of the parent widget.
If the sibling reference is a string it will be a valid selector string and not contain any pseudo selectors ('next()'/'prev()').
| Type: | Percent | SiblingReference |
| Settable: | Yes |
This property can only be set via constructor. Once set, it cannot change anymore.
Static Properties
next
A SiblingReference indicating the next widget in the list of children attached to the same parent. Used by the reference property. Also available as LayoutData.next.
| Type: | unique symbol |
| Settable: | No |
prev
A SiblingReference indicating the previous widget in the list of children attached to the same parent. Used by the reference property. Also available as LayoutData.prev.
| Type: | unique symbol |
| Settable: | No |
Related Types
ConstraintValue
- JavaScript Type:
tabris.Constraint,tabris.Widget,tabris.Percent,Symbol,Array,Object,string,numberortrue. - TypeScript Type:
tabris.ConstraintValue
A ConstraintValue represents a constraint on the layout of a widget that the parent uses to determine the position of one of its edges. This type allows various expressions that can all be used in place of a Constraint instance for convenience. All API that accept these expressions will convert them to a Constraint object. (With the exception of CanvasContext.)
Every expression of ConstraintValue consists of a SiblingReference and/or an offset value.
In addition to Constraint instances ConstraintValue includes:
Offset-only constraints
Simply the Offset number by itself, a positive float including zero. A value of true is also accepted and treated like zero.
Examples:
widget.left = 12.5;
widget.right = 8;
widget.top = 0;
widget.bottom = true;
Reference-only constraints
Either a PercentValue or a SiblingReferenceValue.
Examples:
widget.left = '12%';
widget.right = 'prev()';
widget.top = new Percent(50);
widget.bottom = '#foo';
ConstraintLikeObject
A plain object implementing the following interface:
- JavaScript Type:
Object - TypeScript Type:
tabris.ConstraintLikeObject
interface ConstraintLikeObject {
reference?: SiblingReferenceValue | PercentValue;
offset?: Offset;
}
An object implementing the same properties as Constraint.
An instances of Constraint is a valid ConstraintLikeObject, but ConstraintLikeObject is less strict: The reference property can be a PercentValue or a SiblingReferenceValue, or can be omitted if offset is given. Either of the two entries may be omitted, but not both.
Examples:
widget.left = {reference: sibling, offset: 12};
widget.right = {reference: '23%', offset: 12};
widget.top = {reference: Constraint.prev};
widget.bottom = {offset: 12};
ConstraintArrayValue
- JavaScript Type:
Array - TypeScript Type:
tabris.ConstraintArrayValue
An array tuple in the format of [reference, offset], where reference is either a PercentValue or a SiblingReferenceValue, and offset is an Offset, i.e. a number.
Examples:
widget.left = [sibling, 0];
widget.right = ['#foo', 0];
widget.top = [{percent: 23}, 12];
widget.bottom = [Constraint.prev, 12];
ConstraintString
- JavaScript Type:
string - TypeScript Type:
tabris.ConstraintString
This is often the most compact way to express a constraint, but it may not be the preferred way in TypeScript projects if type safety is a priority. The string consists of a space separated list of two values in the pattern of 'reference offset'. The reference part may be of any string as accepted by SiblingReferenceValue or PercentValue. The offset has to be a positive (including zero) float, just like Offset.
Examples:
widget.left = '.bar 0';
widget.right = '#foo 0'
widget.top = '23% 12';
widget.bottom = 'prev() 12';
SiblingReference
- JavaScript Type:
tabris.Widget,Symbol,string - TypeScript Type:
tabris.SiblingReference
A SiblingReference indicates a single sibling of a given Widget. Differs from the type SiblingReferenceValue in that it does not include 'next() and 'prev()' as selectors strings. It uses symbols instead. There are three variants of SiblingReference:
Sibling instance
- JavaScript Type:
Widget - TypeScript Type:
tabris.Widget
Any widget instance that has the same parent.
SiblingSelectorString
- JavaScript Type:
string - TypeScript Type:
tabris.SiblingSelectorString
A simple selector string of the format '#Type', '#id', '.class'. No child selectors. The first matching sibling is selected.
SiblingReferenceSymbol
- JavaScript Type:
Symbol - TypeScript Type:
tabris.SiblingReferenceSymbol
The constants Constraint.prev and Constraint.next (also available as LayoutData.prev and LayoutData.next) may be used to point to the sibling directly before/after the reference widget in the parents children list.
SiblingReferenceValue
- JavaScript Type:
tabris.Widget,Symbol,string - TypeScript Type:
tabris.SiblingReferenceValue
Same as SiblingReference, but less strict in that it also allows the strings 'next() and 'prev()' in place of the prev and next symbols.
Offset
- JavaScript Type:
number - TypeScript Type:
tabris.Offset, an alias fornumber
A positive or negative float, or 0, representing device independent pixels (DIP).
