Flex 3快速入门（18）: 构建高级用户界面 添加拖放支持
?
<mx:Application
??? xmlns:mx="http://www.adobe.com/2006/mxml"
??? width="365" height="225"
??? creationComplete="creationCompleteHandler();"
>
??? <mx:Script>
??????? <![CDATA[
??????????????? private function creationCompleteHandler():void
??????????????? {
??????????????????? srclist.dataProvider = ['Reading', 'Skating', 'Movies'];???????
??????????????????? destlist.dataProvider = [];
??????????????? }
??????? ]]>
??? </mx:Script>
??? <mx:Panel title="Select activities" layout="horizontal">
??????? <mx:VBox width="50%">
??????????? <mx:Label text="Available activities"/>
??????????? <!-- Drag initiator -->
??????????? <mx:List
??????????????? id="srclist" width="100%" height="100"
??????????????? allowMultipleSelection="true"???????????????
??????????????? dragEnabled="true"
??????????? />
??????? </mx:VBox>
??????? <mx:VBox width="50%">
??????????? <mx:Label text="Activities I enjoy"/>
??????????? <!-- Drop target -->
??????????? <mx:List
??????????????? id="destlist" width="100%" height="100"
??????????????? dropEnabled="true"
??????????? />
??????? </mx:VBox>
??? </mx:Panel>
</mx:Application>
结果
通过拖放操作移动元素
默认的时候dragMoveEnable等于false，那么只允许你从过一个List控件复制元素到另一个List控件中。如果你修改该上边的例子，在源List控件中，增加dragMoveEnabled属性，并且设置为true。那么就向下边的例子那样，可以移动和复制元素了。
默认的动作是移动元素，在拖动的过程中按住Control键，可以复制元素。
例子
<!-- Drag initiator -->
<mx:List
??? id="srclist" width="100%" height="100"
??? allowMultipleSelection="true"???????????????
??? dragEnabled="true"??? dragMoveEnabled="true"
/>
双向拖放功能
你可以允许双向拖放，通过把两个列表的dragEnabled和dropEnabled属性都设置为true。就像下边：
<!-- Both drag initiator and drop target -->
<mx:List
??? id="srclist" width="100%" height="100"
??? allowMultipleSelection="true"???????????????
??? dragEnabled="true"??? dropEnabled="true"
??? dragMoveEnabled="true"
/><!-- . . . -->
<!-- Both drag initiator and drop target -->
<mx:List
??? id="destlist" width="100%" height="100"
??? allowMultipleSelection="true"???????????????
??? dragEnabled="true"??? dropEnabled="true"
??? dragMoveEnabled="true"
/>
结果
手工添加拖放功能
想要让非基于list的控件或容器支持拖放操作，必须明确的添加一系列指定的类和方法。使用DragManager,DragSource和DragEvent类来实现拖放操作。
Flex应用程序使用时间来控制拖放操作。
拖动开始事件
当你把一个控制设置为“拖动开始点”，你可以使用mouseDown，mouseMove和dragComplete事件来管理拖放操作。
关于mouseDown和mouseMove事件
mouseDown事件在用户用鼠标选中并且按下鼠标键开始分发。mouseMove时间在鼠标移动的时候开始分发。
下边的例子嵌入了4个欧元硬币（1分，2分，5分，10分）图片，兵器使用Image控件显示他们。在每一个Image控件中，监听mouseMove事件并且定义事件处理器方法，这个方法被命名为dragIt()。在dragIt()方法中，使用事件的currentTarget属性，获得事件源硬币图片的引用，然后吧这个引用放入到drageInitiator这个本地变量中。
下一步，创建一个DragSource实例，并且调用她的addData()方法来保存dragIt方法的value参数。使用字符串"value"来描述value参数的格式。一会，当你创建“放下目标”时，你将使用这个字符串，来检查是否允许一个元素，放到某个组件上。
想要显示一个硬币图片作为用户拖动它的标志，需要创建一个图片实例，这个图片与“拖动开始点”的图片是一样的。把这个图片保存在dragProxy这个本地变量中。
最后，调用DragManager的静态方法doDrag()，并且把图片发生点，拖动源，事件对象，和拖动代理类传送给它，开始拖动操作。
你可以随意拖动硬币，但是在任何地方都放不下它。因为你还没有定义“放下目标”。下一节，将讲述如何定义“放下目标”。
例子
<?xml version="1.0" encoding="utf-8"?>
<mx:Application
??? xmlns:mx="http://www.adobe.com/2006/mxml"????
??? viewSourceURL="src/DragAndDropDragInitiatorEvents/index.html"??? width="500" height="160"
>
??? <mx:Script>
??????? <![CDATA[??????????? import mx.managers.DragManager;
??????????? import mx.core.DragSource;
???????????
??????????? // Embed the various Euro coin images. Images originally
??????????? // from Wikipedia (http://en.wikipedia.org/wiki/Euro_coins)
??????????? [Embed("assets/1c.png")]??????????? [Bindable]
??????????? public var OneCent:Class;
???????????
??????????? [Embed("assets/2c.png")]??????????? [Bindable]
??????????? public var TwoCents:Class;
???????????
??????????? [Embed("assets/5c.png")]??????????? [Bindable]
??????????? public var FiveCents:Class;
???????????
??????????? [Embed("assets/10c.png")]??????????? [Bindable]
??????????? public var TenCents:Class;??????????? private function dragIt(event:MouseEvent, value:uint):void
??????????? {??????????????? // Get the drag initiator component from the event object.
??????????????? var dragInitiator:Image = event.currentTarget as Image;
???
??????????????? // Create a DragSource object.
??????????????? var dragSource:DragSource = new DragSource();
???
??????????????? // Add the data to the object.??????????????? dragSource.addData(value, 'value');
???
??????????????? // Create a copy of the coin image to use as a drag proxy.
??????????????? var dragProxy:Image = new Image();
??????????????? dragProxy.source = event.currentTarget.source;
???
??????????????? // Call the DragManager doDrag() method to start the drag.??????????????? DragManager.doDrag(dragInitiator, dragSource, event, dragProxy);
??????????? }??????? ]]>
??? </mx:Script>
???
??? <mx:HBox>??????? <mx:Image
??????????? id="oneCent" source="{OneCent}"
??????????? mouseMove="dragIt(event, 1);"??????? />
??????? <mx:Image
??????????? id="twoCents" source="{TwoCents}"
??????????? mouseMove="dragIt(event, 2);"??????? />
??????? <mx:Image
??????????? id="fiveCents" source="{FiveCents}"
??????????? mouseMove="dragIt(event, 5);"??????? />
??????? <mx:Image
??????????? id="tenCents" source="{TenCents}"
??????????? mouseMove="dragIt(event, 10);"??????? />???????
??? </mx:HBox>
???
</mx:Application>
“放下目标”
一个放下目标可以使用多种事件，最重要的事件是dragEnter,dragDrop和dragExit时间。
dragEnter事件
dragEnter事件在带有“拖动代理(drag proxy)”鼠标从外部进入“放下目标”的时候分发。一个组件要作为“放下目标”必须定义这个事件监听器。在这个监听器中，你可以改变“放下目标”的外观，从而向用户提供一个反馈，表明这个组件可以接受拖动操作。例如你可以在“放下目标”周围画一个框，或者给“放下目标”一个焦点。
dragExit事件
dragExit事件在用户鼠标没有在“放下目标”上放下，而是移除鼠标的时候分发。如果在dragEnter或其他事件中修改了“放下目标”的外观，你可以在这个事件中恢复到正常的外观。
dragDrop事件
dragDrop事件在用户在“放下目标”上放开鼠标的时候分发。你可以使用这个事件监听器向“放下目标”中增加drag的数据。
在下边的例子中，创建一个Box容器担当“放下目标”，并且定义dragEnter,dragExit和dragDrop事件监听器。Box容器包含一个Label控件，用来显示放到Box上的硬币的总和
在dragEnter事件监听器中，检查拖动源对象中是否包含value格式。只有对象包含这个格式才可以被放到这个“放下目标”上。如果包含，给用户一个可视化的反馈，通过变粗Box容器的。通过调用DragManager的acceptDrapDrop方法，告诉DragManager,Box容器要接受这个“拖动开始点”。
在dragExit的事件监听器中，恢复Box的外观以表明“拖动代理”已经不在它上边了。
最后，在drapDrop的事件监听器中，当用户把硬币放到“放下目标”上时获得调用，用硬币的值增加totalValue的值，并且回复Box的外观，以表明放下操作完成。
例子
<?xml version="1.0" encoding="utf-8"?><mx:Application
??? xmlns:mx="http://www.adobe.com/2006/mxml"
??? width="525" height="270"
???? viewSourceURL="src/DragAndDropDragDropTargetEvents/index.html"
>??? <mx:Script>
??????? <![CDATA[
??????????? import mx.events.DragEvent;
??????????? import mx.containers.Box;
??????????? import mx.managers.DragManager;
??????????? import mx.core.DragSource;
???????????
??????????? // Embed the various Euro coin images. Images originally??????????? // from Wikipedia (http://en.wikipedia.org/wiki/Euro_coins)
??????????? [Embed("assets/1c.png")]
??????????? [Bindable]
??????????? public var OneCent:Class;
???????????
??????????? [Embed("assets/2c.png")]??????????? [Bindable]
??????????? public var TwoCents:Class;
???????????
??????????? [Embed("assets/5c.png")]??????????? [Bindable]
??????????? public var FiveCents:Class;
???????????
??????????? [Embed("assets/10c.png")]??????????? [Bindable]
??????????? public var TenCents:Class;
???????????
??????????? [Bindable]??????????? private var totalValue:uint;
??????????? private function dragIt(event:MouseEvent, value:uint):void
??????????? {??????????????? // Get the drag initiator component from the event object.
??????????????? var dragInitiator:Image = event.currentTarget as Image;
???
??????????????? // Create a DragSource object.
??????????????? var dragSource:DragSource = new DragSource();
???
??????????????? // Add the data to the object.??????????????? dragSource.addData(value, 'value');
???
??????????????? // Create a copy of the coin image to use as a drag proxy.
??????????????? var dragProxy:Image = new Image();
??????????????? dragProxy.source = event.currentTarget.source;
???
??????????????? // Call the DragManager doDrag() method to start the drag.??????????????? DragManager.doDrag(dragInitiator, dragSource, event, dragProxy);
??????????? }??????????? // Called if the user drags a drag proxy onto the drop target.
??????????? private function dragEnterHandler(event:DragEvent):void
??????????? {??????????????? // Get the drop target component from the event object.
??????????????? var dropTarget:Box=event.currentTarget as Box;
???
??????????????? // Accept the drag only if the user is dragging data
??????????????? // identified by the 'value' format value.??????????????? if (event.dragSource.hasFormat('value'))
??????????????? {
??????????????????? // Make the border of the Box thicker to
??????????????????? // visually signal to the user that they can
??????????????????? // drop the coin there.??????????????????? dropTarget.setStyle("borderThickness", 5);
???????????????????
??????????????????? // Accept the drop.
??????????????????? DragManager.acceptDragDrop(dropTarget);
??????????????? }
??????????? }???????????
??????????? // Called if the user drags the drag proxy away from the drop target.
??????????? private function dragExitHandler(event:DragEvent):void
??????????? {??????????????? // Get the drop target component from the event object.
??????????????? var dropTarget:Box=event.currentTarget as Box;???????????????
???????????????
??????????????? // Set the border of the Box to its default value
??????????????? // to visually indicate that the user is no longer
??????????????? // over the drop target.??????????????? revertBoxBorder();???????????????
??????????? }???????????????????
???????????
??????????? // Called if the target accepts the dragged object and the user
??????????? // releases the mouse button while over the drop target.
??????????? private function dragDropHandler(event:DragEvent):void
??????????? {??????????????? // Get the data identified by the color format from the drag source.
??????????????? var value:uint = event.dragSource.dataForFormat('value') as uint;??????????????? // Add the value to the total
??????????????? totalValue += value;
???????????????
??????????????? // Set the border of the Box to its default value
??????????????? revertBoxBorder();???????????????
??????????? }
???????????
??????????? // Helper method to revert the Box's border to a 1 pixel outline.
??????????? private function revertBoxBorder():void??????????? {
??????????????? amountDisplay.setStyle("borderThickness", 1);???????????????
??????????? }
??????? ]]>
??? </mx:Script>???
??? <mx:HBox>
??????? <mx:Image
??????????? id="oneCent" source="{OneCent}"
??????????? mouseMove="dragIt(event, 1);"??????? />
??????? <mx:Image
??????????? id="twoCents" source="{TwoCents}"
??????????? mouseMove="dragIt(event, 2);"??????? />
??????? <mx:Image
??????????? id="fiveCents" source="{FiveCents}"
??????????? mouseMove="dragIt(event, 5);"??????? />
??????? <mx:Image
??????????? id="tenCents" source="{TenCents}"
??????????? mouseMove="dragIt(event, 10);"??????? />???????
??? </mx:HBox>
???
??? <mx:Box
??????? id="amountDisplay"
??????? borderStyle="solid" borderColor="#000000" backgroundColor="#FFFFFF"??????? width="100%" height="100" horizontalAlign="center" verticalAlign="middle"
??????? dragEnter="dragEnterHandler(event);"
??????? dragExit="dragExitHandler(event);"
??????? dragDrop="dragDropHandler(event);"??? >
??????? <mx:Label text="{totalValue + ' pence'}" fontSize="48"/>???????
??? </mx:Box>???
</mx:Application>
结果
??