解决使用layui的时候form表单中的select等不能渲染的问题

  $("#father").append("<form class=\"layui-form\" lay-filter='test' > " +
    "<div class=\"layui-form-item\" >\n" +
    "  <label class=\"layui-form-label\">学院班级:</label>\n" +
    "  <div class=\"layui-input-inline\" >\n" +
    "   <select name=\"ucollege\">\n" +
    "    <option value=\"\">请选择专业</option>\n" +
    "    <option value=\"浙江\" selected=\"\">浙江省</option>\n" +
    "    <option value=\"你的工号\">江西省</option>\n" +
    "    <option value=\"你最喜欢的老师\">福建省</option>\n" +
    "   </select>\n" +
    "  </div>\n" +
    "  <div class=\"layui-input-inline\">\n" +
    "   <select name=\"ugrade\" >\n" +
    "    <option value=\"\">请选择班级</option>\n" +
    "    <option value=\"杭州\">杭州</option>\n" +
    "    <option value=\"宁波\" disabled=\"\">宁波</option>\n" +
    "    <option value=\"温州\">温州</option>\n" +
    "    <option value=\"温州\">台州</option>\n" +
    "    <option value=\"温州\">绍兴</option>\n" +
    "   </select>\n" +
    "  </div>\n" +
    "</div>" +
    " <div class=\"layui-form-item\">\n" +
    "  <label class=\"layui-form-label\">性别:</label>\n" +
    "  <div class=\"layui-input-block\">\n" +
    "   <input type=\"radio\" name=\"usex\" value=\"男\" title=\"男\" checked=\"\">\n" +
    "   <input type=\"radio\" name=\"usex\" value=\"女\" title=\"女\">\n" +
    "  </div>\n" +
    " </div>" +
    "</form>");
  //添加按钮
  $("#father").append("<div style=\"margin-left: 120px;\">\n" +
    "    <button type=\"button\" class=\"layui-btn layui-btn-primary layui-btn-radius\" onclick=\"addUserFinish()\">添 加</button>\n" +
    "    <button type=\"button\" class=\"layui-btn layui-btn-primary layui-btn-radius\">重 置</button>\n" +
    "  </div>");

  layui.use('form', function(){
    var form = layui.form; //只有执行了这一步，部分表单元素才会自动修饰成功
    form.render();
    form.render('select' ,'test'); //刷新select选择框渲染
  });
}