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ConstraintLayout

Package | spark.layouts
Class | public class ConstraintLayout
Inheritance | ConstraintLayout LayoutBase OnDemandEventDispatcher Object
Subclasses | FormItemLayout

Language Version : | ActionScript 3.0

Product Version : | Flex 4.5

Runtime Versions : | Flash Player 10, AIR 1.5

The ConstraintLayout class arranges the layout elements based on their individual settings and a set of constraint regions defined by constraint columns and constraint rows. Although you can use all of the properties and constraints from BasicLayout to position and size elements, ConstraintLayout gives you the ability to create sibling-relative layouts by constraining elements to the specified columns and rows.

Note: The Spark list-based controls (the Spark List control and its subclasses such as ButtonBar, ComboBox, DropDownList, and TabBar) do not support the ConstraintLayout class. Do not use ConstraintLayout with the Spark list-based controls.

Per-element supported constraints are `left`, `right`, `top`, `bottom`, `baseline`, `percentWidth`, and `percentHeight`. Element's minimum and maximum sizes will always be respected.

Columns and rows may have an explicit size or content size (no explicit size). Explicit size regions will be fixed at their specified size, while content size regions will stretch to fit only the elements constrained to them. If multiple content size regions are spanned by an element, the space will be divided equally among the content size regions.

The measured size of the container is calculated from the elements, their constraints, their preferred sizes, and the sizes of the rows and columns. The size of each row and column is just big enough to hold all of the elements constrained to it at their preferred sizes with constraints satisfied. The measured size of the container is big enough to hold all of the columns and rows as well as any other elements left at their preferred sizes with constraints satisfied.

During a call to the `updateDisplayList()` method, the element's size is determined according to the rules in the following order of precedence (the element's minimum and maximum sizes are always respected):

- If the element has `percentWidth` or `percentHeight` set, then its size is calculated as a percentage of the available size, where the available size is the region or container size minus any `left`, `right`, `top`, or `bottom` constraints.
- If the element has both left and right constraints, it's width is set to be the region's or container's width minus the `left` and `right` constraints.
- If the element has both `top` and `bottom` constraints, it's height is set to be the container's height minus the `top` and `bottom` constraints.
- The element is set to its preferred width and/or height.

The element's position is determined according to the rules in the following order of precedence:

- If element's baseline is specified, then the element is positioned in the vertical direction such that its `baselinePosition` (usually the base line of its first line of text) is aligned with `baseline` constraint.
- If element's `top` or `left` constraints are specified, then the element is positioned such that the top-left corner of the element's layout bounds is offset from the top-left corner of the container by the specified values.
- If element's `bottom` or `right` constraints are specified, then the element is positioned such that the bottom-right corner of the element's layout bounds is offset from the bottom-right corner of the container by the specified values.
- When no constraints determine the position in the horizontal or vertical direction, the element is positioned according to its x and y coordinates.

The content size of the container is calculated as the maximum of the coordinates of the bottom-right corner of all the layout elements and constraint regions.

Public Properties
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| Property | Defined By
--- | --- | ---
|  | clipAndEnableScrolling : Boolean If true, specifies to clip the children to the boundaries of the viewport. | LayoutBase
|  | constraintColumns : Vector.<ConstraintColumn> A Vector of ConstraintColumn instances that partition the target container. | ConstraintLayout
|  | constraintRows : Vector.<ConstraintRow> A Vector of ConstraintRow instances that partition the target container. | ConstraintLayout
|  | dropIndicator : DisplayObject The DisplayObject that this layout uses for the drop indicator during a drag-and-drop operation. | LayoutBase
|  | horizontalScrollPosition : Number The x coordinate of the origin of the viewport in the component's coordinate system, where the default value is (0,0) corresponding to the upper-left corner of the component. | LayoutBase
|  | target : GroupBase The GroupBase container whose elements are measured, sized and positioned by this layout. | LayoutBase
|  | typicalLayoutElement : ILayoutElement Used by layouts when fixed row/column sizes are requested but a specific size isn't specified. | LayoutBase
|  | useVirtualLayout : Boolean A container can hold any number of children. | LayoutBase
|  | verticalScrollPosition : Number The y coordinate of the origin of the viewport in the component's coordinate system, where the default value is (0,0) corresponding to the upper-left corner of the component. | LayoutBase

Public Methods
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| Method | Defined By
--- | --- | ---
|  | ConstraintLayout() Constructor. | ConstraintLayout
|  | addEventListener(type:String, listener:Function, useCapture:Boolean = false, priority:int = 0, useWeakReference:Boolean = false):void | OnDemandEventDispatcher
|  | calculateDropLocation(dragEvent:DragEvent):DropLocation Calculates the drop location in the data provider of the drop target for the specified dragEvent. | LayoutBase
|  | clearVirtualLayoutCache():void When useVirtualLayout is true, this method can be used by the layout target to clear cached layout information when the target changes. | LayoutBase
|  | dispatchEvent(event:Event):Boolean | OnDemandEventDispatcher
|  | elementAdded(index:int):void Called by the target after a layout element has been added and before the target's size and display list are validated. | LayoutBase
|  | elementRemoved(index:int):void This method must is called by the target after a layout element has been removed and before the target's size and display list are validated. | LayoutBase
|  | getElementBounds(index:int):Rectangle Returns the specified element's layout bounds as a Rectangle or null if the index is invalid, the corresponding element is null, includeInLayout=false, or if this layout's target property is null. | LayoutBase
|  | getHorizontalScrollPositionDelta(navigationUnit:uint):Number Returns the change to the horizontal scroll position to handle different scrolling options. | LayoutBase
|  | getNavigationDestinationIndex(currentIndex:int, navigationUnit:uint, arrowKeysWrapFocus:Boolean):int Delegation method that determines which item to navigate to based on the current item in focus and user input in terms of NavigationUnit. | LayoutBase
|  | getScrollPositionDeltaToElement(index:int):Point Computes the verticalScrollPosition and horizontalScrollPosition deltas needed to scroll the element at the specified index into view. | LayoutBase
|  | getVerticalScrollPositionDelta(navigationUnit:uint):Number Returns the change to the vertical scroll position to handle different scrolling options. | LayoutBase
|  | hasEventListener(type:String):Boolean | OnDemandEventDispatcher
|  | hideDropIndicator():void Hides the previously shown drop indicator, created by the showDropIndicator() method, removes it from the display list and also stops the drag scrolling. | LayoutBase
|  | measure():void Measures the target's default size based on its content, and optionally measures the target's default minimum size. | LayoutBase
|  | removeEventListener(type:String, listener:Function, useCapture:Boolean = false):void | OnDemandEventDispatcher
|  | showDropIndicator(dropLocation:DropLocation):void Sizes, positions and parents the drop indicator based on the specified drop location. | LayoutBase
|  | updateDisplayList(width:Number, height:Number):void Sizes and positions the target's elements. | LayoutBase
|  | updateScrollRect(w:Number, h:Number):void Called by the target at the end of its updateDisplayList to have the layout update its scrollRect. | LayoutBase
|  | willTrigger(type:String):Boolean | OnDemandEventDispatcher

Protected Methods
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| Method | Defined By
--- | --- | ---
|  | calculateDragScrollDelta(dropLocation:DropLocation, elapsedTime:Number):Point Calculates how much to scroll for the specified dropLocation during a drag and drop gesture. | LayoutBase
|  | calculateDropIndex(x:Number, y:Number):int Returns the index where a new item should be inserted if the user releases the mouse at the specified coordinates while completing a drag and drop gesture. | LayoutBase
|  | calculateDropIndicatorBounds(dropLocation:DropLocation):Rectangle Calculates the bounds for the drop indicator that provides visual feedback to the user of where the items will be inserted at the end of a drag and drop gesture. | LayoutBase
|  | getElementBoundsAboveScrollRect(scrollRect:Rectangle):Rectangle Returns the bounds of the first layout element that either spans or is above the scrollRect's top edge. | LayoutBase
|  | getElementBoundsBelowScrollRect(scrollRect:Rectangle):Rectangle Returns the bounds of the first layout element that either spans or is below the scrollRect's bottom edge. | LayoutBase
|  | getElementBoundsLeftOfScrollRect(scrollRect:Rectangle):Rectangle Returns the bounds of the first layout element that either spans or is to the left of the scrollRect's left edge. | LayoutBase
|  | getElementBoundsRightOfScrollRect(scrollRect:Rectangle):Rectangle Returns the bounds of the first layout element that either spans or is to the right of the scrollRect's right edge. | LayoutBase
|  | getScrollRect():Rectangle Returns the bounds of the target's scroll rectangle in layout coordinates. | LayoutBase
|  | layoutContent(unscaledWidth:Number, unscaledHeight:Number):void Lays out the elements of the layout target using the current widths and heights of the columns and rows. | ConstraintLayout
|  | measureAndPositionColumnsAndRows(constrainedWidth:Number, constrainedHeight:Number):void Used by FormItemLayout to measure and set new column widths and row heights before laying out the elements. | ConstraintLayout
|  | scrollPositionChanged():void Called when the verticalScrollPosition or horizontalScrollPosition properties change. | LayoutBase

Property Detail

constraintColumns | property

`constraintColumns:Vector.<ConstraintColumn>`

Language Version : | ActionScript 3.0

Product Version : | Flex 4.5

Runtime Versions : | Flash Player 10, AIR 1.5

A Vector of ConstraintColumn instances that partition the target container. The ConstraintColumn instance at index 0 is the left-most column; indices increase from left to right.

Implementation
`public function get constraintColumns():Vector.<ConstraintColumn>`
`public function set constraintColumns(value:Vector.<ConstraintColumn>):void`

constraintRows | property |

`constraintRows:Vector.<ConstraintRow>`

Language Version : | ActionScript 3.0

Product Version : | Flex 4.5

Runtime Versions : | Flash Player 10, AIR 1.5

A Vector of ConstraintRow instances that partition the target container. The ConstraintRow instance at index 0 is the top-most column; indices increase from top to bottom.

Implementation
`public function get constraintRows():Vector.<ConstraintRow>`
`public function set constraintRows(value:Vector.<ConstraintRow>):void`
Constructor Detail

ConstraintLayout | () | Constructor

`public function ConstraintLayout()`

Language Version : | ActionScript 3.0

Product Version : | Flex 4.5

Runtime Versions : | Flash Player 10, AIR 1.5

Constructor.

Method Detail

layoutContent | () | method

`protected function layoutContent(unscaledWidth:Number, unscaledHeight:Number):void`

Language Version : | ActionScript 3.0

Product Version : | Flex 4.5

Runtime Versions : | Flash Player 10, AIR 1.5

Lays out the elements of the layout target using the current widths and heights of the columns and rows. Used by FormItemLayout after setting new column widths to lay elements using those new widths.

Parameters

| `unscaledWidth:Number` — Specifies the width of the component, in pixels, in the component's coordinates, regardless of the value of the `scaleX` property of the component.
| `unscaledHeight:Number` — Specifies the height of the component, in pixels, in the component's coordinates, regardless of the value of the `scaleY` property of the component.

measureAndPositionColumnsAndRows | () | method |

`protected function measureAndPositionColumnsAndRows(constrainedWidth:Number, constrainedHeight:Number):void`

Language Version : | ActionScript 3.0

Product Version : | Flex 4.5

Runtime Versions : | Flash Player 10, AIR 1.5

Used by FormItemLayout to measure and set new column widths and row heights before laying out the elements.

Parameters

| `constrainedWidth:Number` (default = `NaN`)`` — The total width available for columns to stretch or shrink their percent width columns. If NaN, percent width columns are unconstrained and fit to their content.
| `constrainedHeight:Number` (default = `NaN`)`` — The total height available for rows to stretch or shrink their percent height rows. If NaN, percent height rows are unconstrained and fit to their content.

Wed Nov 15 2017, 09:50 AM +01:00