extjs 中的combobox不显示下拉的值啊，有时候又显示。

Question

 <script type="text/javascript">
        var app = {};
        function onDomReady() {
            Ext.QuickTips.init();
    Ext.form.Field.prototype.msgTarget = 'side';
    
    var school = new Ext.data.Record.create([ 
            {name:'SchoolID'}, 
            {name:'SchoolName'}
        ]); 
    var schooldata = {'totalCount':'5','root':[{ 
        ProfessionID:'1',  
        SchoolName:'信息学院'
    },{ 
        ProfessionID:'11',  
        SchoolName:'经管学院'
    },{ 
        ProfessionID:'12',  
        SchoolName:'水土保持学院'
    },{ 
        ProfessionID:'13',  
        SchoolName:'人文学院'
    },{ 
        ProfessionID:'14',  
        SchoolName:'计算机科学学院'
    }]};     app.schoolStore = new Ext.data.Store({ 
            idProperty: 'SchoolID', 
            proxy:new Ext.data.MemoryProxy(schooldata), 
            reader:new Ext.data.JsonReader({ 
                root:'root',totalProperty:'totalCount'   
            },school) 
        });                    
    
            app.professiondata = [['1','信息','信息学院','信息专业','0'],['2','计算机','信息学院','计算机','0'],['4','軟件','信息学院','軟件工程','0'],['5','土木','','土木工程專業','0'],['6','電子','','電子商務專業','0']];
            
            app.professionStore = new Ext.data.Store(
                {
                    proxy:new Ext.data.MemoryProxy(app.professiondata),
                    reader:new Ext.data.ArrayReader(
                    {},[{name:"ProfessionID"},{name:"ProfessionName"},{name:"SchoolName"},{name:"ProfessionDesc"},{ name: 'IsDelete' }]
                    )
                }
            );  
            
         var bBar = new Ext.Toolbar({
            applyTo: 'bToolBar',
            autoHeight: true,
            autoWidth: true,
            buttonAlign: 'center',
            items:
            [
            { text: '针对本页选中项：',xtype:'tbtext' }, '-',
            { text: '新建', scope: this , handler: newProfession }
             , '-',
             { text: '删除', scope: this  , handler: deleteProfession }
             , '-',
             { text: '撤销删除', scope: this  , handler: unDeleteProfession }
            ]
        });                   var professionsm = new Ext.grid.CheckboxSelectionModel();
            var professioncm = new Ext.grid.ColumnModel([
                new Ext.grid.RowNumberer,
                professionsm,
              { dataIndex: 'ProfessionID', header: '专业ID', id: 'ProfessionID', sortable: true },
          { dataIndex: 'ProfessionName', header: '专业名称', id: 'ProfessionName',sortable: true } ,
          { dataIndex: 'SchoolName', header: '所属学院', id: 'SchoolName',sortable: true } ,
          { dataIndex: 'ProfessionDesc', header: '专业简介',renderer:qtip },
          { dataIndex: 'IsDelete', header: '是否删除',renderer:deleteFlagShow },
          { dataIndex: 'ProfessionID', header: '编辑', id: 'editClassID',renderer:editProfessionInfo }
        ]);
            professioncm.defaultSortable = true;            app.professionGrid = new Ext.grid.GridPanel({
                id: 'ProfessionInfo',
                title: '专业信息管理',
                store: app.professionStore,
                cm: professioncm,
                sm: professionsm,
                enableColLock: false,
                collapsed: false,
                loadMask: true,
                autoHeight: true,
                autoWidth: true,
                el: 'grid-main',
                autoExpandColumn: 'ProfessionName',
                stripeRows: true,
                trackMouseOver: true,
                bbar:bBar,
                loadMask: { msg: "数据加载中，请稍等..." } 
            });
            app.schoolStore.load();
            app.professionGrid.render();
            app.professionStore.load();
        }
        Ext.onReady(onDomReady);
        
        function deleteFlagShow(value)
        {
            value = value.trim();
            if(value == "1")
            {
                return "已删除";
            }
            else if(value == "0")
            {
                return "未删除";
            }
            else
            {
                return "";
            }
        }
        
        function qtip(val)
        {
            val = val.trim();
            var subVal = val;
            if(val.length > 50)
            {
                subVal = val.substring(0,50) + "......";
            }
            return '<span style="display:table;width:100%;" qtip='+val+'>'+subVal+'</span>';
        }
        
        function editProfessionInfo(value)
        {
            value = value.trim();
            return "<a href='#' style='padding:2px 10px 2px 10px;' onclick='editProfession("+ value +");return false;'>编辑</a>";
        }          
        
        var newProfessionPanel;
        newProfessionPanel = new Ext.Panel({
            title: '专业信息管理-新建专业 ',
            layout: 'form',
            contentEl: 'mainPanelForm_body',
            frame: false,
            header:false,
            bodyStyle: 'background-color:#FFFFFF;',
            applyTo: 'mainPanelForm',
            autoHeight: true,
            autoWidth: true,
            bodyBorder: false,
            boder: false,
            buttonAlign: 'center',
            collapsible: false,
            collapsed: false,
            items:
            [
                {
                    xtype: 'fieldset',
                    title: '',
                    autoHeight: true,
                    layout: 'form',
                    labelAlign: 'right',
                    buttonAlign: 'center',
                    bodyStyle: 'padding:5px;',
                    items:
                        [
                            new Ext.form.TextField(
                            {
                                fieldLabel: '专业名',
                                name: 'newProfessionName',
                                id: 'newProfessionName',
                                allowBlank: false,
                                growMax: 30
                            }),
                             new Ext.form.ComboBox(
                                {
                                    forceSelection: true,
                                    fieldLabel: '所属学院',
                                    id: 'newProfessionSchool',
                                    name: 'newProfessionSchool',
                                    store:app.schoolStore,
                                    valueField:'SchoolID',
                                    displayField:'SchoolName',
                                    triggerAction: 'all',
                                    mode:'local',
                                    lazyRender: true,
                                    hiddenName:'newProfessionSchoolID',
                                    width: 110
                                }),
                             new Ext.form.TextArea(
                            {
                                width:200,
                                grow:true,
                                maxLength:800,
                                fieldLabel: '专业简介',
                                name: 'newProfessionNote',
                                id: 'newProfessionNote',
                                allowBlank: true
                            })
                    ]
                }
             ]
        });
        
     app.newProfessionWin = new Ext.Window(
            {
                el: 'newProfessionWin',
                layout: 'fit',
                width: 380,
                height: 210,
                title: '新建专业',
                closeAction: 'hide',
                maximizable:true,
                minimizable: true,
                constrainHeader: true,
                buttonAlign: 'center',
                modal:true,
                items: [newProfessionPanel],
                buttons:
                [
                    { text: '新建', scope: this, handler: newProfessionOpt }, { text: '取消', scope: this, handler: function() { app.newProfessionWin.hide(); } }
                ]
            }
        );
       function newProfession() {            
        app.newProfessionWin.show();
    }
请问各位，combobox为什么有时候显示，有时候点击，下拉有没有，这个是怎么回事啊。我也改过，mode : 'remote',也没有用。大家帮忙看看，即使是下拉出現，无论怎么选都值出现第一个“ 信息学院”Ext JSComboBox函数

Answer 1

没有人在啊，各位高手看看啊。