Question

I’m trying to achieve something which I’m sure is pretty simple but I cannot see the wood for the trees. I have created a simple control which inherits from link button which contains a list of a simple object called LinkParamaters, the idea being that in markup you can define a postback url as well as parameters which then returns the PostBackUrl property to include a querystring. This was working as expected until I wanted to data bind the parameters within a repeater. I then started to get the following Parser Error:

Databinding expressions are only supported on objects that have a DataBinding event. UI.Controls.LinkParameter does not have a DataBinding event.

So I figured I obviously needed to implement a data bind event. maybe there is an interface I need to implement, I couldn’t find one. Sadly I’ve just moved jobs so don’t have access to reflector at the moment so could not drill down into the code but I could see that Control has these events/methods, inheriting the parameter object from Control solved the parser error but unsurprisingly didn’t resolve the binding and it doesn’t make sense anyway as it’s not a control.

The Link button code :

[ParseChildren(true, DefaultProperty = "Parameters")]
public class QueryLinkButton : LinkButton
{

    private String _url = null;

    public QueryLinkButton()
    {
        this.Parameters = new List<LinkParameter>();
    }

    public override String PostBackUrl
    {
        get
        {
            return _url ?? (_url = BuildUrl());
        }
        set
        {
            base.PostBackUrl = value;
        }
    }

    [PersistenceMode(PersistenceMode.InnerDefaultProperty)]
    public List<LinkParameter> Parameters { get; set; }

    private String BuildUrl()
    {
        //Build URL to Include Query String Params           
    }

}

public class LinkParameter 
{

    public String Name { get; set; }

    public String Value { get; set; }

}

And then the Asp Code :

 <custom:QueryLinkButton runat="server" ID="EventLink" Text="View Accommodation" PostBackUrl="HotelCriteria.aspx">
       <custom:LinkParameter runat="server" Name="EventID" Value='<%# Eval("EventID")%>'/>
  </custom:QueryLinkButton>

I’ve got around the problem for now by handling this server side but it really kind of negates what I was trying to do creating the custom control as I wanted to define these things purely in the mark-up. Even just a link to an article to get me started will be much appreciated as I’ve googled for so long and could only find similar problems but not the same thing but that is most likely to poor search criteria.

Thanks in advance

Paul

Answer 1

I managed to fix this in the end by using my brain, I’m not 100% confident it is the ideal solution but it does make sense to me and more importantly this silly little problem is now working :0).

I got my LinkParameter class to derive from DataBoundControl and then overrode the DataBind method on the custom control and then told each parameter to perform it’s DataBind method:

    public override void DataBind()
    {
        base.DataBind();
        foreach (LinkParameter param in Parameters)
        {
            param.DataBind();
        }
    }

If anyone has a cleaner, more efficient solution then please let me know.

Thanks

Paul