/// <summary>
/// Converts an instance of a markup extension to formatted output text.
/// If any exceptions or error conditions occur (like not finding the
/// requested markup extenstion processor by name) error output is returned
/// instead. Under no circumstances should this method raise an exception
/// up to the calling code. The only thing not protected by the try/catch
/// are calls to GetErrorOutput which is designed to not throw exceptions.
/// </summary>
/// <param name="name">The tag name of the markup extension, e.g. HtmlHelpers.Date.</param>
/// <param name="parameters">The parameters specified in the markup extension tag.</param>
/// <returns>Formatted text to replace the markup extension.</returns>
private string Process(string name, string[] parameters)
{
string output = String.Empty;
try
{
string nameLowered = name.ToLower(); // Keys are normalized to be all lower case.
if (_handlers.ContainsKey(nameLowered) == true)
{
Func <MarkupExtensionHandler> getHandlerDelegate = _handlers[nameLowered];
MarkupExtensionHandler handler = getHandlerDelegate();
output = handler.Process(parameters);
}
else
{
output = GetErrorOutput(String.Format("Unknown markup extension. No markup extension with the name \"{0}\" has been loaded.", name));
}
}
catch (MarkupExtensionException mex)
{
// Catch any MarkupExtensionExceptions in the code above or from any handlers and output the error response according to "returnHandlerErrorsAsOutput" configuration.
output = GetErrorOutput(mex.Message);
}
catch (Exception ex)
{
// Do the same thing as for a MarkupExtensionException for now but in the future when we have better logging, may want to do something different here.
output = GetErrorOutput(ex.Message);
}
return(output);
}
/// <summary>
/// Allows derived classes to add handlers to the internal _handlers dictionary,
/// normalizing the markup extension name to be lower case.
/// </summary>
/// <param name="name">
/// The name of the markup extension as used in the tag, e.g. HtmlHelpers.Date.
/// </param>
/// <param name="handlerDelegate">
/// A delegate that returns an instance of a MarkupExtensionHandler capable of processing
/// the named markup extension.
/// </param>
protected void Add(Func <MarkupExtensionHandler> handlerDelegate)
{
// Instantiate an instance to get its name.
MarkupExtensionHandler handler = handlerDelegate();
string name = handler.Name;
// Add the delegate to the dictionary, keyed by name.
_handlers.Add(name.ToLower(), handlerDelegate);
}
