Flex4相对FLex3的组件变化

customizations much more straightforward. Here is a table showing Flex 3 Halo components and their Flex 4 beta Spark counterparts: Flex 3 Halo Component Flex 4 beta Spark Component
mx.controls.Button spark.components.Button
mx.controls.ButtonBar spark.components.ButtonBar
mx.controls.CheckBox spark.components.CheckBox
mx.controls.ComboBox spark.components.DropDownList (w/o editability)
mx.controls.HorizontalList spark.components.List (with a HorizontalLayout)
mx.controls.HRule spark.primitives.Line
mx.controls.HScrollBar spark.components.HScrollBar
mx.controls.HSlider spark.components.HSlider
mx.controls.Image spark.primitives.BitmapImage
mx.controls.LinkBar spark.components.ButtonBar (with a custom skin)
mx.controls.LinkButton spark.components.Button (with a custom skin)
mx.controls.List spark.components.List
mx.controls.NumericStepper spark.components.NumericStepper
mx.controls.RadioButton spark.components.RadioButton
mx.controls.RadioButtonGroup spark.components.RadioButtonGroup
mx.controls.TextArea spark.components.TextArea
mx.controls.TextInput spark.components.TextInput
mx.controls.TileList spark.components.List (with a TileLayout)
mx.controls.ToggleButtonBar spark.components.ButtonBar
mx.controls.VideoDisplay spark.components.VideoPlayer
mx.controls.VRule spark.primitives.Line
mx.controls.VScrollBar spark.components.VScrollBar
mx.controls.VSlider spark.components.VSlider

mx.core.Application spark.components.Application
mx.core.Window spark.components.Window
mx.core.WindowedApplication spark.components.WindowedApplication
mx.containers.Canvas spark.components.Group
mx.containers.HBox spark.components.HGroup
mx.containers.Panel spark.components.Panel
mx.containers.Tile spark.components.Group (with a TileLayout)
mx.containers.VBox spark.components.VGroup

Adobe encourages you to use Halo components and containers along with Spark components. Because Adobe continues to build components atop the same base class (UIComponent), there should be full interoperability between Spark and Halo. Here is a table of the components and containers that do not currently have direct Spark equivalent classes.

Flex 3 classes with no direct Flex 4 beta counterpart
mx.controls.Alert
mx.controls.ColorPicker
mx.controls.DataGrid
mx.controls.DateChooser
mx.controls.DateField
mx.controls.Menu
mx.controls.MenuBar
mx.controls.PopUpButton
mx.controls.PopUpMenuButton
mx.controls.ProgressBar
mx.controls.RichTextEditor
mx.controls.TabBar
mx.controls.Tree
mx.containers.Accordion
mx.containers.ApplicationControlBar
mx.containers.ControlBar
mx.containers.DividedBox
mx.containers.Form
mx.containers.Grid
mx.containers.TabNavigator
mx.containers.TitleWindow
mx.containers.ViewStack

Changes in states syntax
Flex 4 beta has promoted the states functionality to a full MXML language feature. As a result, you will likely find states to be much more flexible and direct. The new states syntax is more inline, allowing state-specific changes to be specified in context. Here are the key differences in the Flex 4 beta syntax:

Only states are defined within the states array.
In the new states syntax, you cannot use de>AddChildde> and de>RemoveChildde>. Instead, you define a component's role in a particular state on the component itself using the de>includeInde> and de>excludeFromde> attributes.
In the following Flex 3 example, states are used to include a Button and remove a TextInput only when the de>currentStatede> of the document is de>submitStatede>. This approach can get very verbose with more complex states.

<mx:states>    <mx:State name="submitState" basedOn="">        <mx:AddChild relativeTo="{loginForm}" >           <mx:Button label="submit" bottom="10" right="10"/>        </mx:AddChild>        <mx:RemoveChild target="{firstTextInput}"/>    </mx:State></mx:states> <mx:TextInput id="firstTextInput" /><mx:Canvas id="loginForm" />
Here is the simpler Flex 4 beta code using de>includeInde> and de>excludeFromde>.

<s:states>    <s:State name="submitState" /></s:states><s:TextInput id="firstTextInput" excludeFrom="submitState" /><s:Group id="loginForm" >    <s:Button label="submit" bottom="10" right="10" includeIn="submitState"/></s:Group>
de>SetPropertyde>, de>SetStylede>, and de>SetEventHandlerde> have been replaced by a new dot syntax, which allows you to qualify MXML attribute values with a specific state identifier.
In the following Flex 3 example, the code defines a property, style, and event for a Button in de>submitStatede>.

<mx:states>    <mx:State name="submitState" basedOn="">        <mx:SetProperty target="{submitButton}" name="label" value="submit" />        <mx:SetStyle target="{submitButton}" name="textDecoration" value="underline"/>        <mx:SetEventHandler target="{submitButton}" name="click" handler="trace('done');"/>    </mx:State>    <mx:State name="clearState" basedOn="">        <mx:SetProperty target="{submitButton}" name="label" value="clear" />        de><mx:SetEventHandler target="{submitButton}" name="click" de>handler="emptyDocument()" />    </mx:State></mx:states> <mx:Button id="submitButton" />
In Flex 4 beta, the code looks like this:

<s:states>    <s:State name="submitState" />    <s:State name="clearState" /></s:states> <s:Button label.submitState="submit" textDecoration.submitState="underline"   click.submitState="trace('done')" click.clearState="emptyDocument()"   label.clearState="clear" textDecoration.clearState="none"/>
A component can no longer be in an undefined or null state. By default, the first declared state is the initial state of a component.
The new syntax is available when a document uses the MXML 2009 language namespace. You cannot mix the legacy syntax and the new states syntax. The old syntax is available only in the MXML 2006 namespace.
Additionally, each component now supports a set of states defined in its skin class, which makes it simpler to apply visual changes depending on the state of a component. For example, if you look at the skin for the Spark Button, you will find the following states defined:

<s:states>    <s:State name="up" />    <s:State name="over" />    <s:State name="down" />    <s:State name="disabled" /></s:states>
The ButtonSkin class defines what happens visually to a Spark Button in each one of these states.

This is only a brief introduction to the new Flex 4 beta states syntax. Visit the Enhanced States Syntax Spec to find more details.