Flex DataGrid 默认情况下的排序方式
DataGridColumn的属性sortCompareFunction和sortDescending是点击列头后的排序方式，而要确定默认情况下的排序方式是无效的。那么怎么办？
查看datagrid的官方代码就会知道如何给datagrid默认排序，下面是官方代码：
private function updateSortIndexAndDirection():void
{
// Don't show sort indicator if sortableColumns is false or if the
// column sorted on has sortable="false"
if (!sortableColumns)
{
lastSortIndex = sortIndex;
sortIndex = -1;
if (lastSortIndex != sortIndex)
invalidateDisplayList();
return;
}
if (!dataProvider)
return;
var view:ICollectionView = ICollectionView(dataProvider);
var sort:Sort = view.sort;
if (!sort)
{
sortIndex = lastSortIndex = -1;
return;
}
var fields:Array = sort.fields;
if (!fields)
return;
if (fields.length != 1)
{
lastSortIndex = sortIndex;
sortIndex = -1;
if (lastSortIndex != sortIndex)
invalidateDisplayList();
return;
}
// fields.length == 1, so the collection is sorted on a single field.
var sortField:SortField = fields[0];
var n:int = _columns.length;
sortIndex = -1;
for (var i:int = 0; i < n; i++)
{
if (_columns[i].dataField == sortField.name)
{
sortIndex = _columns[i].sortable ? i : -1;
sortDirection = sortField.descending ? "DESC" : "ASC";
return;
}
}
}
可以这样实现：
<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" creationComplete="init()">
<mx:Script>
<![CDATA[
import mx.collections.SortField;
import mx.collections.Sort;
import mx.utils.ObjectUtil;
import mx.collections.ArrayCollection;
[Bindable]
private var adg:ArrayCollection = new ArrayCollection([{name:"张三华",age:15,sex:"男"},
{name:"李四国",age:45,sex:"男"},
{name:"王七花",age:24,sex:"女"},
{name:"赵华柳",age:17,sex:"女"},
{name:"田三华",age:33,sex:"男"},]);
private function init():void{
adg.sort = new Sort();
adg.sort.fields = [new SortField("age",false,true)];
adg.refresh();
dg.dataProvider = adg;
}
private function sortRanges(obj1:Object,obj2:Object):int{
var value1:Number = obj1.age;
var value2:Number = obj2.age;
if(value1 > value2 ){
return 1;
}else if(value1 < value2 ){
return -1;
}else{
return 0;
}
}
private function dataFilter():void{
if(adg.filterFunction == null){
adg.filterFunction = dataFilter2;
}
adg.refresh();
}
private function dataFilter2(item:Object):Boolean{
var bool:Boolean = true;
var it:String = item["name"];
var filter:String = ti.text;
if(!it || it.toLowerCase().indexOf(filter.toLowerCase()) < 0){
bool = false;
}
return bool;
}
private function sortCompare(obj1:Object,obj2:Object):int{
return ObjectUtil.numericCompare(obj1.age,obj2.age);
}
]]>
</mx:Script>
<mx:DataGrid id="dg" x="89" y="46" width="552" height="160">
<mx:columns>
<mx:DataGridColumn headerText="name" dataField="name"/>
<mx:DataGridColumn headerText="age" dataField="age"/>
<mx:DataGridColumn headerText="sex" dataField="sex" />
</mx:columns>
</mx:DataGrid>
<mx:Form>
<mx:FormItem>
<mx:TextInput id="ti" change="dataFilter()"/>
</mx:FormItem>
</mx:Form>
</mx:Application>
重点是黑体字部分，SortField第一个参数是排序的字段，第二个参数用来确定是否区分大小写，第三个参数表示是否按降序排列。
参考官方SortField构造函数就明白了：
/**
* Constructor.
*
* @param name The name of the property that this field uses for
* comparison.
* If the object is a simple type, pass <code>null</code>.
* @param caseInsensitive When sorting strings, tells the comparitor
* whether to ignore the case of the values.
* @param descending Tells the comparator whether to arrange items in
* descending order.
* @param numeric Tells the comparitor whether to compare sort items as
* numbers, instead of alphabetically.
*
* @langversion 3.0
* @playerversion Flash 9
* @playerversion AIR 1.1
* @productversion Flex 3
*/
public function SortField(name:String = null,
caseInsensitive:Boolean = false,
descending:Boolean = false,
numeric:Object = null)
{
super();
_name = name;
_caseInsensitive = caseInsensitive;
_descending = descending;
_numeric = numeric;
_compareFunction = stringCompare;
}
下面补充： 点击DataGridColumn列头后的排序方式的原因（官方代码），关注属性sortCompareFunction和sortDescending
/**
* @private
*/
private function headerReleaseHandler(event:DataGridEvent):void
{
if (!event.isDefaultPrevented())
{
manualSort = true;
sortByColumn(event.columnIndex);
manualSort = false;
}
}
/**
* @private
*/
private function sortByColumn(index:int):void
{
var c:DataGridColumn = columns[index];
var desc:Boolean = c.sortDescending;
// do the sort if we're allowed to
if (c.sortable)
{
var s:Sort = collection.sort;
var f:SortField;
if (s)
{
s.compareFunction = null;
// analyze the current sort to see what we've been given
var sf:Array = s.fields;
if (sf)
{
for (var i:int = 0; i < sf.length; i++)
{
if (sf[i].name == c.dataField)
{
// we're part of the current sort
f = sf[i]
// flip the logic so desc is new desired order
desc = !f.descending;
break;
}
}
}
}
else
s = new Sort;
if (!f)
f = new SortField(c.dataField);
c.sortDescending = desc;
var dir:String = (desc) ? "DESC" : "ASC";
sortDirection = dir;
// set the grid's sortIndex
lastSortIndex = sortIndex;
sortIndex = index;
sortColumn = c;
// if you have a labelFunction you must supply a sortCompareFunction
f.name = c.dataField;
if (c.sortCompareFunction != null)
{
f.compareFunction = c.sortCompareFunction;
}
else
{
f.compareFunction = null;
}
f.descending = desc;
s.fields = [f];
}
collection.sort = s;
collection.refresh();
}