1.检查是否在page指令中添加了mastertype 声明.
2.如果要使用set/get textbox 值，则不要执行findcontrol，而是在masterpage 中定义一个公共属性以进行设置并获取它，然后从页面中调用此属性.

1. Check whether you have added the mastertype declaration in the page directive.
2. if you want to use set/get the textbox value then instead of doing a findcontrol define a public property in the masterpage for setting and getting it and then call this property from the page.

我的第一个猜测是您的控件实际上不在母版页上，而是在嵌套页上.如果是这样，将找不到它.您将需要执行以下操作:

My first guess would be that your control is not actually on the master page but on a nested page. If so, this won''t find it. You would need to do something like:

this.Form.FindControl("txtEmployee_code");

您可以在此处找到更多示例和更多想法(请务必查看评论，因为它们还有其他人尝试过的选项):
http://csharporcas.blogspot.com/2006/05/master-page-find- control.html [^ ]

You can find more examples and more ideas here (make sure to look at the comments, since they have other options people have tried):
http://csharporcas.blogspot.com/2006/05/master-page-find-control.html[^]

尝试TextBox tb =(TextBox)Page.FindControl("txtEmployee_code");

try TextBox tb = (TextBox)Page.FindControl("txtEmployee_code");