<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" creationComplete="initApp()" layout="vertical" fontSize="12" backgroundColor="white">

 <mx:Script>
  <![CDATA[

   import mx.collections.ArrayCollection;

   [Bindable]
   private var AC1:ArrayCollection;

   private function initApp():void{
    AC1=new ArrayCollection([{name:"开会",type:"紧急",steps:"0"},
     {name:"结算",type:"一般",steps:"0"},
     {name:"放假",type:"一般",steps:"0"}]);

}

   protected function fun_AddImage(event:MouseEvent):void
   {
    trace(AC1);

    for(var i:int=0; i<AC1.length; i++) {
     trace(AC1[i].steps);

    } 
   }

  ]]>
 </mx:Script>

 <mx:DataGrid rowCount="4" dataProvider="{AC1}" id="dg" >
  <mx:columns>
   <mx:DataGridColumn headerText="name" dataField="name"/>
   <mx:DataGridColumn headerText="type" dataField="type"/>
   <mx:DataGridColumn headerText="email">
    <mx:itemRenderer>
     <mx:Component>
      <mx:TextInput text="{data.steps}"/>
     </mx:Component>
    </mx:itemRenderer>
   </mx:DataGridColumn>
  </mx:columns>
 </mx:DataGrid>

 <mx:Button x="326" y="513" label="测试数据" click="fun_AddImage(event)"/>

</mx:Application>

调试提示：
warning: unable to bind to property 'steps' on class 'Object' (class is not an IEventDispatcher)

现在需要的效果是在DG的输入框里修改了文字后，数组ac1的steps字段也会更着修改
点测试后出现的数字是在DG中输入的数字，现在的问题应该是自定义的列无法和数据源ac1中的steps绑定的问题。

/*如果数据只是文本的,下面的代码就可以完成你要的功能
* 注意   editable="true" 
*如果是复杂的数据类型,需要在列中定义 itemEditor="{new ClassFactory(XXXX)}" 
*<<  狗狗熊 奉上  >>
*/

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" creationComplete="initApp()" layout="vertical" fontSize="12" backgroundColor="white">
 <mx:Script>
  <![CDATA[
   import mx.collections.ArrayCollection;
   [Bindable]
   private var AC1:ArrayCollection;
   private function initApp():void{
    AC1=new ArrayCollection([{name:"开会",type:"紧急",steps:"0"},
     {name:"结算",type:"一般",steps:"0"},
     {name:"放假",type:"一般",steps:"0"}]);
   }

   protected function fun_AddImage(event:MouseEvent):void
   {
    trace(AC1);

    for(var i:int=0; i<AC1.length; i++) {
     trace(AC1[i].steps);

    } 
   }

  ]]>
 </mx:Script>
 <mx:DataGrid rowCount="4" dataProvider="{AC1}" id="dg"  editable="true"   >
  <mx:columns>
   <mx:DataGridColumn headerText="name" dataField="name" editable="false"/>
   <mx:DataGridColumn headerText="type" dataField="type" editable="false"/>
   <mx:DataGridColumn headerText="email" dataField="steps" />
  </mx:columns>
 </mx:DataGrid>
 <mx:Button x="326" y="513" label="测试数据" click="fun_AddImage(event)"/>
 </mx:Application>

AC1=new ArrayCollection([{name:"开会",type:"紧急",steps:"0"},
     {name:"结算",type:"一般",steps:"0"},
     {name:"放假",type:"一般",steps:"0"}]);
 }
改成：
var array1:Array = [{name:"开会",type:"紧急",steps:"0"},
    {name:"结算",type:"一般",steps:"0"},
    {name:"放假",type:"一般",steps:"0"}];
var array2:Array = new Array();
for(var i:int = 0;i<array1.length;i++){
    array2.push(new ObjectProxy(array1[i]));
}
AC1 = new ArrayCollection(array2);

原因：ObjectProxy实现了IEventDispatcher接口