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();

}