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.

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