BasicLayout

(Preview)

Package	spark.layouts
Class	public class BasicLayout
Inheritance	BasicLayout LayoutBase OnDemandEventDispatcher Object

Language Version:

ActionScript 3.0

Product Version:

Flex 4

Runtime Versions:

Flash Player 10, AIR 1.5

The BasicLayout class arranges the layout elements according to their individual settings, independent of each-other. BasicLayout, also called absolute layout, requires that you explicitly position each container child. You can use the x and y properties of the child, or constraints to position each child.

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

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

The measured size of the container is calculated from the elements, their constraints and their preferred sizes. The measured size of the container is big enough to fit in all of the elements at their preferred sizes with their constraints satisfied.

Here are some examples of how measured size is calculated:

If the container has a single element with left constraint specified, then the container's measured width will be equal to the element's preferred width plus the value of the left constraint.
If the container has a single element with percentWidth specified, then the container's measured width will be equal to the element's preferred width. Even though the element's percentWidth is not directly factored in the calculations, it will be respected during a call to the updateDisplayList() method.
If the container has a single element with baseline constraint specified, then the container's measured height will be equal to the element's preferred height plus the baseline and minus the value of the element's baselinePosition property.
If the container has a single element with verticalCenter constraint specified, then the container's measured height will be equal to the element's preferred height plus double the value of the verticalCenter constraint.

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 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 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 BasicLayout class calculates its minimum size as the maximum of the minimum child sizes:

For each child in the container, determine the minimum size to which the child could shrink:
- If the child is constrained to its parent's width or height, then the child could shrink to its minimum width or height. Use the minimum size of the child.
- If the child is not constrained to the parent, then it remains at its preferred size. Use the preferred size of the child.
Find the maximum of the sizes from step 1.

Therefore, if a child is constrained to its parent, then the layout uses the child's minimum size. Otherwise, it uses its preferred size of the child to calculate the minimum size for the container.

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

The horizontalCenter or verticalCenter constraints specify the distance between the container's center and the element's center. Set the horizontalCenter or verticalCenter constraints to zero to center the element within the container in the horizontal or vertical direction.
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.

MXML Syntax expanded

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The <s:BasicLayout> tag inherits all of the tag attributes of its superclass and adds no additional tag attributes:

  <s:BasicLayout/>

More examples

About Spark layouts
Set the layout of a Spark container
Set the padding and gap of a layout
Set the alignment of a layout
Set the row height or column width of a layout

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
		constructor : Object A reference to the class object or constructor function for a given object instance.	Object
		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
		BasicLayout() Constructor.	BasicLayout
		addEventListener(type:String, listener:Function, useCapture:Boolean = false, priority:int = 0, useWeakReference:Boolean = false):void Registers an event listener object with an EventDispatcher object so that the listener receives notification of an event.	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 Dispatches an event into the event flow.	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 Checks whether the EventDispatcher object has any listeners registered for a specific type of event.	OnDemandEventDispatcher
		hasOwnProperty(name:String):Boolean Indicates whether an object has a specified property defined.	Object
		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
		isPrototypeOf(theClass:Object):Boolean Indicates whether an instance of the Object class is in the prototype chain of the object specified as the parameter.	Object
		measure():void Measures the target's default size based on its content, and optionally measures the target's default minimum size.	LayoutBase
		propertyIsEnumerable(name:String):Boolean Indicates whether the specified property exists and is enumerable.	Object
		removeEventListener(type:String, listener:Function, useCapture:Boolean = false):void Removes a listener from the EventDispatcher object.	OnDemandEventDispatcher
		setPropertyIsEnumerable(name:String, isEnum:Boolean = true):void Sets the availability of a dynamic property for loop operations.	Object
		showDropIndicator(dropLocation:DropLocation):void Sizes, positions and parents the drop indicator based on the specified drop location.	LayoutBase
		toLocaleString():String Returns the string representation of this object, formatted according to locale-specific conventions.	Object
		toString():String Returns the string representation of the specified object.	Object
		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
		valueOf():Object Returns the primitive value of the specified object.	Object
		willTrigger(type:String):Boolean Checks whether an event listener is registered with this EventDispatcher object or any of its ancestors for the specified event type.	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
		scrollPositionChanged():void Called when the verticalScrollPosition or horizontalScrollPosition properties change.	LayoutBase

Constructor Detail

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Package spark.layouts