我有以下代码，可以滚动到特定的孩子。它工作正常，除非滚动到最后一个孩子。它工作正常，但这不是我期望的行为。问题是当滚动到最后一个孩子时，我希望孩子像其他孩子一样显示在视口的顶部。一些图表应该比文字更好地帮助这一点。
总结问题：
1.当滚动到最后一个孩子时，是否可以将它定位在视口中的（0,0）？
2.我有6个孩子，每个孩子身高200。contentHeight为1200，当verticalScrollPosition为0时，我调用viewport.getVerticalScrollPositionDelta(NavigationUnit.END)，返回值为900。那么900是怎么计算出来的呢？
以下是代码：
<?xml version="1.0" encoding="utf-8"?>
<s:Application
xmlns:fx="http://ns.adobe.com/mxml/2009"
xmlns:s="library://ns.adobe.com/flex/spark"
xmlns:mx="library://ns.adobe.com/flex/mx"
creationComplete="init()"
>
<fx:Script>
<![CDATA[
import components.MockUI;
import mx.collections.ArrayList;
import spark.core.NavigationUnit;
private function init():void {
createElements();
}
private function createElements():void {
for (var i:int = 0; i<6; i++) {
var ui:MockUI = new MockUI();
ui.text = "I'm " + i + " !";
ui.width = 300;
ui.height = 200;
viewport.addElement(ui);
}
}
//scroll to diffrent child, take attetion to the scrollRect
private function scrollToChild(index:int):void {
var delta:Number = returnSumHeight(index);
viewport.verticalScrollPosition = delta;
var scrollRect:Rectangle = viewport.scrollRect;
trace("viewport contentHeight: ", viewport.contentHeight);
trace("vp: ", viewport.verticalScrollPosition);
trace("scrollRect: ", scrollRect);
}
private function handleScroll(unit:uint):void {
trace("unit: ", unit);
var delta:Number = viewport.getVerticalScrollPositionDelta(unit);
trace("delta:", delta);
}
private function minus():void {
viewport.verticalScrollPosition -= 10;
trace("vp: ", viewport.verticalScrollPosition);
}
//return the sum height of children before index item
private function returnSumHeight(index:int):Number {
var sumHeight:Number = 0;
for(var i:int=0; i<index; i++) {
sumHeight += viewport.getElementAt(i).height;
}
return sumHeight;
}
]]>
</fx:Script>
<s:layout>
<s:VerticalLayout horizontalAlign="center" paddingTop="100"/>
</s:layout>
<s:HGroup>
<s:Label text="Select Child: "/>
<s:ComboBox id="comboBox"
dataProvider="{new ArrayList([0,1,2,3,4,5])}"
selectedIndex="0"
change="scrollToChild(comboBox.selectedIndex)"/>
</s:HGroup>
<s:Scroller>
<s:VGroup id="viewport" width="350" height="300" gap="0">
</s:VGroup>
</s:Scroller>
<s:Button label="MINUS" click="minus()"/>
<s:Button label="UP" click="handleScroll(NavigationUnit.UP)"/>
<s:Button label="DOWN" click="handleScroll(NavigationUnit.DOWN)"/>
<s:Button label="HOME" click="handleScroll(NavigationUnit.HOME)"/>
<s:Button label="END" click="handleScroll(NavigationUnit.END)"/>
</s:Application>
莫奎：
package components {
public class MockUI extends UIComponent {
private var label:Label;
private var _text:String;
private var textChanged:Boolean = false;
public function set text(value:String):void {
if(value == _text) {
return;
}
_text = value;
textChanged = true;
invalidateProperties();
}
public function get text():String {
return _text;
}
override protected function createChildren():void {
super.createChildren();
label = new Label();
addChild(label);
}
override protected function commitProperties():void {
super.commitProperties();
if(textChanged) {
textChanged = false;
label.text = _text;
}
}
override protected function updateDisplayList(unscaledWidth:Number, unscaledHeight:Number):void {
super.updateDisplayList(unscaledWidth, unscaledHeight);
label.width = unscaledWidth/2.0;
label.height = unscaledHeight/2.0;
label.x = unscaledWidth/2.0;
label.y = unscaledHeight/2.0;
graphics.clear();
graphics.lineStyle(2, 0xffff00);
graphics.drawRect(0, 0, unscaledWidth, unscaledHeight);
graphics.beginFill(0xff0000, 1);
graphics.drawRect(0,0,unscaledWidth, unscaledHeight);
graphics.endFill();
}
}
}