关于Ext弹出多个Ext.MessageBox和她的结构

Ext.Msg.alert("提示","不能关闭当前窗口");
    var t = new Ext.Button({
            text: '确定',
            handler: function(){
            dlg.hide();
            },
            hideMode: 'offsets'
        });
    var dlg = new Ext.Window({
            autoCreate : true,
            title:"提示",
            resizable:false,
            constrain:true,
            constrainHeader:true,
            minimizable : false,
            maximizable : false,
            stateful: false,
            modal: true,
            shim:true,
            buttonAlign:"center",
            //width:400,
            //height:100,
            //minHeight: 80,
            plain:true,
            footer:true,
            html:'不能关闭当前窗口',
            closable:true,
            close : function(){
            dlg.hide();
            },
            fbar: new Ext.Toolbar({
                items: [t],
                enableOverflow: false
            })
        });
    dlg.show();