Best way to intercept control rendering

I have a control used in our CMS and we don't have the source code for it, what I would like to do is ch开发者_StackOverflowange the rendered output of this control.

Now, I could have a check in my base Page class that checks if the control is being used on the page and then change the html that needs to be altered, but that seems a bit excessive for just 1 usage.

So is there any other way of changing the behaviour of the control without the source code? I'm thinking not other than the way described above.

Thanks

Wrap it in a custom control:

public class MyCMSControl: CommercialCMSControl
{
    protected override void Render(HtmlTextWriter writer)
    {
        StringBuilder stringBuilder = new StringBuilder();
        StringWriter stringWriter = new StringWriter(stringBuilder );

        using (HtmlTextWriter myWriter = new HtmlTextWriter(stringWriter ))
        {
            base.Render(myWriter);

            string newOutput;
            // the original output is in stringBuilder, do whatever you want, and
            // put it in newOutput


            writer.Write(newOutput);
        }
    }
}

If you want to be able to manipulate the output in code specific to the page, add an event, something like:

public delegate void OnRenderHandler(object sender, string originalOutput, HtmlTextWriter writer)
public OnRenderHandler OnRender;
...
/// before writer.Write above...
if (OnRender!=null) {
    OnRender(this,stringBuilder.ToString(),writer);
}

To make your custom version available in the designer, you need something in web.config

<pages>
  <controls>
    <add namespace="My.Control.Namespace" assembly="My.Control.Assembly" tagPrefix="MyControlsPrefix"/>
  </controls>
</pages>