Passing a web control reference to a User Control base class
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22-03-2021 - |
Frage
I created several user controls - most containing a single web control (text box, drop down, radio button etc) - along with one or more validation controls. The point being to combine control and validation in a single user control.
I created a base class for these user control with some common functionality - setters for several properties of a single web control, specifically CssClass and Style to be set in the control in the ascx.
Eg a single text box with a single required field validator.
Sample code for the base class:
public WebControl ctrl {get; set;} //allow derived class access to this
public string CssClass
{
set { ctrl.CssClass = value; } //allow CssClass to be set in the aspx page
}
Sample code for derived class: (in constructor or control OnInit Event - or ?)
base.ctrl = txt; //tell the base class which web control to apply common properties to.
public string ErrorMessage
{
set { val.ErrorMessage = value;} //this works !
}
Sample code for ascx:
<asp:TextBox ID="txt" Cssclass="input-text-m" maxlength="50" runat="server" />
<asp:RequiredFieldValidator ID="val" runat="server" ControlToValidate="txt"
ErrorMessage="">*</asp:RequiredFieldValidator>
Sample code for aspx:
<uc:TextBox ID="ForeName" Cssclass="input-text-m" maxlength="50"
ErrorMessage="Forename" runat="server"/>
The problem I found was that I couldn't find a way for the derived class to set the base class web control reference before the base classes property setters are called. If I set base.ctrl in the derived class constructor - then the derived class control reference (txt) is still null at this point. If I set base.ctrl in any of the control events - eg OnInit - then this is too late.
So far I have got around the problem by simply not using a base class, and writing the property setter code in the user control class instead, however this means duplication of code, which I was trying to avoid.
Is there a way to inform the base class of the control I want it to set the properties for in advance of them being set - or am I going about things the wrong way...
Lösung
What about calling EnsureChildControls
before any get/set operations and including the set operation for ctrl = txt in EnsureChildControls
? This is pretty standard practice for a normal servercontrol, I would think it would work for UserControls too.
public string CssClass { set { EnsureChildControls(); ctrl.CssClass = value; } }
Override EnsureChildControls
, leaving in the call to base, and set ctrl = txt;
here after the call to base.
More information: http://msdn.microsoft.com/en-us/library/system.web.ui.control.ensurechildcontrols.aspx