input传值问题

<li>

        <input type="text" id="txt2" name="txt2" onfocus="showAndHide('List2','show');" readonly />

        <div class="Menu" id="List2">

          <ul>

            <li><input type="checkbox" value="三元里店" /><span>三元里店1</span></li>

            <li><input type="checkbox" value="a" /><span>a1</span></li>

            <li><input type="checkbox" value="a" /><span>a1</span></li>

            <li><input type="checkbox" value="a" /><span>a</span></li>

            <li><input type="checkbox" value="a" /><span>a</span></li>

            <li class="list-button"><input type="button" value="确定"  onclick="showAndHide('List2','hide');" /></li>

          </ul>

        </div>

      </li>

<script type="text/javascript">

/*下拉*/
  function showAndHide(obj,types){
    var Layer=window.document.getElementById(obj);
    switch(types){
  case "show":
    Layer.style.display="block";
  break;
  case "hide":
    Layer.style.display="none";
  break;
}
  }
  function getValue(obj,str){
    var input=window.document.getElementById(obj);
input.value=str;
  }
  
//文本传值

    window.onload = function(){
    var obox = document.getElementById("List2");
    var cboList = obox.getElementsByTagName("input");
    var oText = document.getElementById("txt2");
    document.getElementById("List2").onclick = function(e){
    var src = e?e.target:event.srcElement;
    if(src.tagName == "INPUT"){