问题
I have a user control that I have written and have added to an ASP.NET page, and functions just fine. However, I am trying to reference a property in the that custom control from code behind, on Page_Load, but cannot, because the variable, which is accessible, for the instance is null.
Is this normal for user controls and Page_Load? And if so, how can I make a reference to the control's instance in order to access its public properties? This is something I need to do before the page is rendered, in order to initialize some variables.
回答1:
You can probably access your user control from the Page_PreRender event.
You can find more documentation about the page life cycle in asp.net here.
回答2:
I had the same issue, and it turned out that I was registering my custom control incorrectly.
Correct Definition:
<%@ Register Src="PeriodControl.ascx" TagName="PeriodControl" TagPrefix="ucs" %>
Incorrect Definition:
<%@ Register TagPrefix="ucs" Namespace="MyWebsite" Assembly="MyWebsite" %>
The only difference was to reference the ascx file directly instead of the control in the assembly. Go figure!?
来源：https://stackoverflow.com/questions/10340610/asp-net-user-control-instance-is-null-when-referenced-on-page-load-on-page-code