下拉选择mui.poppicker.js报错picker.getSelectedItem() is no a function

var userPicker;  
(function($, doc) {  
    $.init();  
    $.ready(function() {  
        //普通示例  
        userPicker = new $.PopPicker();  
        userPicker.setData([{  
            value: 'ywj',  
            text: '董事长 叶文洁'  
        }, {  
            value: 'aaa',  
            text: '总经理 艾AA'  
        }, {  
            value: 'lj',  
            text: '罗辑'  
        }, {  
            value: 'ymt',  
            text: '云天明'  
        }, {  
            value: 'shq',  
            text: '史强'  
        }, {  
            value: 'zhbh',  
            text: '章北海'  
        }, {  
            value: 'zhy',  
            text: '庄颜'  
        }, {  
            value: 'gyf',  
            text: '关一帆'  
        }, {  
            value: 'zhz',  
            text: '智子'  
        }, {  
            value: 'gezh',   
            text: '歌者'  
        }]);  
//      var showUserPickerButton = doc.getElementById('showUserPicker');  
//      var userResult = doc.getElementById('userResult');  
//      setTimeout(function(){  
//          showUserPickerButton.addEventListener('tap', function(event) {  
//              userPicker.show(function(items) {  
//                  userResult.innerText = JSON.stringify(items[0]);  
//                  //返回 false 可以阻止选择框的关闭  
//                  //return false;  
//              });  
//          }, false);  
//      },300)  
    });  
})(mui, document);  

function btnClick() {  
        var btn = userPicker.ok;  
        var showUserPickerButton = document.getElementById('showUserPicker');  
        var userResult = document.getElementById('userResult');  
        userPicker.show(function(items) {  
            userResult.innerText = JSON.stringify(items[0]);  
            //返回 false 可以阻止选择框的关闭  
            //return false;  
        });  
        btn.addEventListener('tap', function(event) {  
            userPicker.hide();  
        }, false);  
}  

<meta charset="UTF-8">  
<div data-role="page" data-dom-cache="true" id="AppLogin">  
    <div class="mui-content">  
            <div class="mui-content-padded">  
                <h5 class="mui-content-padded">普通示例</h5>  
                <button id='showUserPicker' class="mui-btn mui-btn-block" type='button' onClick='btnClick()'>一级选择示例 ...</button>  
                <div id='userResult' class="ui-alert"></div>  
            </div>  
        </div>  
</div>