NOTE Starting with version 15.1 the multi-select parameters for our reporting suite are available out of the box. See the Parameters Overview > Using Parameters > Multi-Value Parameters help topic for more details.
This example demonstrates how to use a custom editor for the report's parameter to implement a multi-select parameter. The ASPxTokenBox control is used as a multi-select parameter editor.
The main idea of this approach is to use a report's parameter to pass a string that contains CategoryIDs separated by the '|' character to the report. Then on the report's DataSourceDemanded event handler the report's DataSource is populated based on the parameter value.
The ASPxDocumentViewer.CustomizeParameterEditors event handler is used to customize the report's parameter editor: assign a required editor (ASPxEditBase class descendant) to the e.Editor property, and specify its Init event. Then use this Init event handler to initialize your custom parameter editor and bind it to the data.
See also:
MVC DocumentViewer extension - Creating a multi-select parameter
MVC DocumentViewer - How to create a custom CheckedComboBox parameter editor with the "Select All" functionality for a report