GetOrCreateElemSharedParam.cs

/// <summary>
        /// Gets or Creates Element's shared param.
        /// </summary>
        /// <param name="elem">Revit Element to get param for</param>
        /// <param name="paramName">Parameter Name</param>
        /// <param name="grpName">Param Group Name (relevant only when Creation takes place)</param>
        /// <param name="paramType">Param Type (relevant only when Creation takes place)</param>
        /// <param name="visible">Param UI Visibility (relevant only when Creation takes place)</param>
        /// <param name="instanceBinding">Param Binding: Instance or Type (relevant only when Creation takes place)</param>
        /// <returns></returns>
        public static Parameter GetOrCreateElemSharedParam(Element elem, string paramName, string grpName, ParameterType paramType, bool visible, bool instanceBinding)
        {
            try
            {
                // Check if existing
                Parameter param = GetElemParam(elem, paramName);
                if (null != param) return param;

                // If here, need to create it...
                BindSharedParamResult res = BindSharedParam(elem.Document, elem.Category, paramName, grpName, paramType, visible, instanceBinding);
                if (res != BindSharedParamResult.eSuccessfullyBound && res != BindSharedParamResult.eAlreadyBound) return null;

                // If here, binding is OK and param seems to be IMMEDIATELY available from the very same command
                return GetElemParam(elem, paramName);
            }
            catch (Exception ex)
            {
                System.Windows.Forms.MessageBox.Show(string.Format("Error in getting or creating Element Param: {0}", ex.Message));
                return null;
            }
        }