User control can't access the parent page's public properties

Question

User-2074302700 posted

Hi Guys

 I have built a page that is contained within a master page and it holds 2 user controls

 
Control A contains a DataList

Control B contains a FormView

 I want to pass the selected index from the DataList on Control A to the FormView on Control B so it acts like a master / detail scenario

 I created a public property on the page that contains both controls called DataListSelectedIndex

 A also created a public property for DataListSelectedIndex on the Control
 

 I populate the DataListSelectedIndex property of the Control when the DataList_SelectedIndexChanged event is fired

 And I populate the DataListSelectedIndex property of the page on the OnLoad event of the page.

 
My problem is that on Control B - (or Control A for that matter) I can't access the public property DataListSelectedIndex

 

The method I am trying to access this is through  - this.Page on the OnLoad even of the Control

 
Can anyone help? Thanks in Advance

 

Dannster

 

 

 

Answer 1

User660069657 posted

The issue is that when you access this.Page through the control you are getting an instance of the base Page object, which does not have a DataListSelectedIndex property. You first need to cast the page object to the actual page you are on. Take a look in your pages codebehind, the class name is the type of page you want. You can then access the property from your page by doing:

((CODEBEHINDCLASSNAME)this.Page).DataListSelectedIndex = VALUE;

  This is bad practice though as it ties your control to a specific page. You can get round this in two ways. Firstly you could write a simple interface:

public interface IDataListClientPage
{
  int DataListSelectedIndex { get; set; }
}

 And implement it in your page using " : IDataListClientPage" after your class definition. You then change the code in the control to:

if (this.Page is IDataListClientPage)
  ((IDataListClientPage)this.Page).DataListSelectedIndex = VALUE;
else
  throw new Exception("Page must implement IDataListClientPage.");

  The other option is to use an event handler, so you put a SelectedIndexChanged event on the datalist and handle it on the page, this would fully decouple the controls for maximum flexibility:

Events in C# 

Answer 2

User-2074302700 posted

Hi Mate

Thanks for your reply, I'm nearly there now - just a couple of issues.

• I cant cast to the class name of the codebehind page (it wont show up in intellisense)
• How can I implement the IDataListClientPage interface if the page class is already Inheriting from  : System.Web.UI.Page?

I tried the event way also - thanks for that - its very complicated for my brain tho at the minute

I have an Issue with not being able to access an instance of ControlA from ControlB

I have created a sample project containing a page which contains 2 user controls

 
Control A (label and a button)

Control B (label and a button)

I created a delegate in the codebehind of ControlA but placed it outside the class for ControlA

I created a separate class for the Event args with one string property

I created an event inside the ControlA class 

I then created a method in ControlA codebehind which raises the event

then I got all confused and didn't know a) how to handle the event in Control B code behind b) Where to subscribe the event

Help much appreciated. - If I can crack this I reckon I'll be sorted.

 
Cheers

Mart
 

 

 

 

Answer 3

User660069657 posted

 To use the interface just change the inhertience to : System.Web.UI.Page, IDataListClientPage

Remember that you can inherit from just one base type, but you can implement as many interfaces as you like.

 

With the events route - you would generally handle the event in your page, and then set the value in control B from the page level. That way B doesn't know where its data comes from. 

Answer 4

User-2074302700 posted

Sorted, I've sussed it now - thanks for the help.

 

I was well baffled for ages because I couldn't reference my controls from my page but there was something goin on in Visual Studio so I restarted it and that did the trick!

 Cheers

 

I still couldn't get this.Page to cast to (_Default) or even cast to the Interface so not sure what i did wrong there, but I don't need that now coz this will do nicely thanks 

 

Martin
 

Answer 5

User-1206211797 posted

May be you need to twik the page like this http://www.dotnetfunda.com/articles/article97.aspx (Pass value from user control to page)

Answer 6

User522004677 posted

This is what I was lookin for:

http://aspalliance.com/67_Accessing_Page_Properties

Thanks ,