How to add skin to custom controls using ASP. NET

Controls extended from the GridView are used in the project. The following is the skin. After skin is extracted from the page and obtained to the skin, the system prompts "undefined mark"

<PC3: GridViewEx CssClass = "table_style" runat = "server" HorizontalAlign = "Center">
<AlternatingRowStyle CssClass = "left_title_2"/>
<RowStyle CssClass = "left_title_1"/>
</PC3: GridViewEx>

Copy this code from the aspx page where the control is used

<% @ Register Assembly = "GViewEx" Namespace = "GViewEx. Controls" TagPrefix = "PC3" %>

Project production successful.

Although it is very simple, it seems that such things have not been found on the Internet, so they are pasted.

By the way, the non-appearance attributes added to the skin will also be applied to the corresponding controls, such

<Columns>
<Asp: BoundField DataField = "id" HeaderText = "no."/>
</Columns>

If the data source bound to the control in the application pool skin does not have the "id" field, an error occurs.