从后面的代码更新时，asp.net隐藏字段不保留值

I'm using a hidden field to store a value in an asp.net page. Basically I set the value of the hidden field whenever a value on the form is changed i.e. first name, date etc. The field is on a webform that has a master page and is in the content section:I'm using a hidden field to store a value in an