Parameters

In the simplest case your extension has no parameters. However, it may be useful to change the behavior of your extension from one project to the other.

The screenshot below, shows an extension with a parameter and which can be edited individually per project:

For example, if your extension copies translated files then the parameter may be the target directory and the Beebox administrator can change the path from one project to the next.

Add parameter

Adding parameters starts with implementing the three methods below:

• ParameterHelp property: Must return a help text. If null then the system assumes that there are no parameters.
• ParameterDefault property: Returns your parameter default value (null or something else). This default value can then be changed in the project settings.
• ValidateParameter() method: This method is called when a user changes the parameter value in a project. Return an error message if the value is not ok.
   

		/// <summary>
		/// Gets optional help description (not html!) of the configuration parameter.
		/// By returning a non-null value, you explicitly tell the Beebox that this extension has a configurable parameter.
		/// </summary>
		public override string ParameterHelp 
		{ 
			get { return "Fill in a filter type, either one of 'alpha', 'beta' or 'gamma'."; } 
		}
 
 
 
		/// <summary>
		/// Gets the default value of the parameter. Default can be changed by user.
		/// </summary>
		public override string ParameterDefault { get { return "alpha"; } }
 
 
 
		/// <summary>
		/// Validates the user parameters.
		/// Return null if ok, otherwise return an error text.
		/// </summary>
		/// <param name="parameter">The parameter edited by a user.</param>
		/// <returns>Null: parameter is ok. Otherwise return an error message.</returns>
		public override string ValidateParameter(string parameter)
		{
			try
			{
				// Note: If the user does not change the default parameter value, this method is not called!
				if (parameter != "alpha" && parameter != "beta" && parameter != "gamma") 
					return "Wrong parameter value!";
				else
					return null;
			}
			catch (Exception e) { return "The parameter is not correct."; }
		}

Note that the ValidateParameters() function is not called if the user leaves the parameter value field empty in the project settings.

The last step is to process the configuration parameter passed to the main method of each extension. Example:

public override bool IsMatch(Segment segment, IExtensionConfiguration configuration)

This interface has a Parameter property. It is null if the default parameter was not changed in the project that triggered your extension. A typical code would look like this:

public override bool IsMatch(Segment segment, IExtensionConfiguration configuration)
{
	// Get parameter. 
	// If null then the default value was not edited in the current Beebox project.
 
	var parameter = configuration.Parameter ?? ParameterDefault;
    if (parameter == "alpha") 
    {
       ....
    }

Mandatory parameter values

If the user does not explicitly configure a parameter value in a project, your extension will be called with a null parameter value. How do you then develop an extension that requires the user to fill in his/her parameter? For example, a server file path that must be supplied but you cannot possible preset with a default value.

The workaround is to add a test to your extension main method. if the parameter is "null" then you would simply do nothing. Sample code:

// We ask user to fill in a file path
public override string ParameterHelp { get { return "Supply log file path."; } }
 
// There is no default value for the path!
public override string ParameterDefault { get { return null; } }
 
public override bool IsMatch(Segment segment, IExtensionConfiguration configuration)
{
	if (configuration.Parameter == null) return false;
    ....

You could also raise an exception though this is not recommended: When triggered from the user interface a generic error message (not your exception text) would be displayed. If the extension is called from an automatic operation, the exception would be logged in the Windows event log.