Physical structure:

An easy to see that the combolist consist of three(body,head,list)main parts these parts are combine to complete the physical structure of the combolist control , in this article I will try to explain  an easy way how to create  combolist control  From Scratch , not nice look one only but also with straight main operations ,methods and properties .

 pic1

as you see above the pic1 contain the three parts are

1-body :the plot where the selected item is placed  

2-head: the plot that we can control the hiding and show the element list.

3-list: the plot that contain all combolist elements(items) 

logical structure of combolist :

we discuss the logical structure  from  three aspects(css,js,and html)

the css to control the style ( make nice  or the dress it up )

the css style is tracing the pic1  three parts.

Code

/*div tag*/
.ComboList
{
    width:200px;
    height:400px;
    margin-left:0px;
    margin-top:0px;
    font-family: 宋体;
    font-size:12px;
    color:black;
    cursor:default;

}

/*span*/
.ComboList .headPar
{
    width:17px;
    height:21px;
    margin-left:182px;
    position:absolute;
    background-image:url('images/combolist.png');
    background-repeat:no-repeat;
    
}

/*input tag*/
.ComboList .bodyPart
{
    border-top: 1px #3D7BAD solid;
    border-bottom: 1px #B7D9ED solid;
    border-left:1px #A4C9E3 solid;
    border-right:1px #A4C9E3 solid;
    height:17px;
    position:absolute;
    width:181px;
    font-family: 宋体;
    font-size:12px;
    color:black;

}
/*ul*/
.ComboList .ListPart
{
    margin-top:21px;
    margin-left:0px;
    height:auto;
    overflow:auto;
    position:absolute;
    width:183px;
    border: 1px #B7D9ED solid;
    border-top:1px transparent solid;
    list-style-type:none;
    display:none;

}
/*li*/
.ListPart .ComboListItem
{
   display:block;
   width:inherit;
   height:21px;
   padding: 1px 0px 0px 3px;
   
   
}
/*when mouse move */
.ComboListItem:hover 
{
 background-image:url('images/BGline.png');
 background-repeat:repeat-x;

}

Java script aspects:

for js point of view we just consider the operation,methods and properties that the combolist have to contain, for example the selected index ,

selected item , add new item,remove item ,and high level operations like sorting of item.

Code



//style nice looking when mouse move,ou,up/

 function changeState( element ,height ,statNumber)
  {
      //statNumber the number of state we want to show currently
      // elemnt is imageBackground for span
     /// 0: normal status,1 mouseMove status,2 mousepress status, 3 fucuse,4 disable ,5 no
     var top=height*statNumber;
      // alert('100% -'+left+'px');
     document.getElementById(element).style.backgroundPosition='100% -'+top+'px';     
    
  }
  
  function chageBorderColorWhenMouseMove(element)
  {
     document.getElementById(element).style.borderBottom='1px #3D7BAD  solid';
     document.getElementById(element).style.borderRight='1px #3D7BAD  solid';
     document.getElementById(element).style.borderLeft='1px #3D7BAD  solid';

  }
   
   function chageBorderColorWhenMouseOut(element)
  {
     document.getElementById(element).style.borderBottom='1px #B7D9ED solid';
     document.getElementById(element).style.borderRight='1px #B7D9ED  solid';
     document.getElementById(element).style.borderLeft='1px #B7D9ED  solid';
  }
  function ShowComboList(element)
  {
    document.getElementById(element).style.display='block';
  }
  
  function HideComboList(element)
  {
    document.getElementById(element).style.display='none';
  }




//----------------------selection and add new items


 var ComboListItemIndex=-1;
 var ComboListSelectedindex=-1;
 var ComboListselectedItem="";
 function ComboListAddNewListItem(ComboxListId)
 {
  
       ComboListItemIndex=ComboListItemIndex+1;
       var NewItemString="<li id=ComboListItem"+ComboListItemIndex+" class=ComboListItem onclick=ComboListSelectedIndex(this);ComboListSelectedItem(this);>item"+ComboListItemIndex+"</li>";
        var listBoxOldElemtns=document.getElementById(ComboxListId).innerHTML;
       var newListboxItem=listBoxOldElemtns+NewItemString;
       document.getElementById(ComboxListId).innerHTML=newListboxItem;

 }
 
 
 // return the  selected index of the combo list
 function ComboListSelectedIndex(elThis)
 {
      
       var name=elThis.id;
       // get the index.
       ComboListSelectedindex=name.charAt((name.length)-1);
       return ComboListSelectedindex;
       
 }
 
 function ComboListSelectedItem(elThis)
   {
       var Item=elThis.innerHTML;
       document.getElementById('InputBody').value=Item;
       HideComboList('ListPart');
       return Item;
   }


//
function ComboListGetItem(index)
   {
    var re="";
    if(index>-1 && index<=ComboListItemIndex)
    {
       var name="ComboListItem"+index;
       re=document.getElementById(name).innerHTML;
    }
    else
    {
     alert('Out Of Rang Index');
    }
     return re;
   }


// SET VALUE IN SPECIFIC INDEX POSITION
 function ComboListSetItem(index,value)
   {
    
    if(index>-1 && index<=ComboListItemIndex)
    {
       var name="ComboListItem"+index;
       document.getElementById(name).innerHTML=value;
    }
    else
    {
     alert('Out Of Rang Index');
    }
   }
   
   // FUNCTION LENGTH;
   
   //-1 for empty.
   function ComboListLength()
   {
     return  ComboListItemIndex;
   }

sorting element of combolist :

whatever you used mean the sorting algorithm ,insertion sort,quicksort ,heapsort ,just invoke the combolist sort method like code below ,

here i used the array  bufferCombolist ,js provide sorting  function for array

html aspect :

from html point of view we just think the combolist as below:

Code
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">

<head>
<meta content="text/html; charset=utf-8" http-equiv="Content-Type" />
<title>Untitled 1</title>
<link rel="stylesheet" type="text/css" href="combolist.css"/>
<script language="javascript" type="text/javascript" src="combolist.js"></script>
</head>

<body>

   <div class="ComboList">
       <span id="HeaderSpan" class="headPar" onmousemove="changeState('HeaderSpan',21,1);chageBorderColorWhenMouseMove('InputBody');"  onmouseout="changeState('HeaderSpan',21,0);chageBorderColorWhenMouseOut('InputBody')"  onmousedown="changeState('HeaderSpan',21,2);ShowComboList('ListPart');"  onmouseup="changeState('HeaderSpan',21,1);"></span>
       <input id="InputBody" class="bodyPart" value=""/>
         <ul id="ListPart" class="ListPart">
          
        </ul>
   </div>

     <a href="#" onclick="ComboListAddNewListItem('ListPart');">add New Item </a>&nbsp;    
     
     <a href="#" onclick="ComboListGetItem('2');">get(i) </a>
     
     &nbsp;
     
     <a href="#" onclick="ComboListSetItem('2','AMMAR');">set(i,value)</a>


</body>

</html>