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 TokenBox extension 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 approach demonstrated in the DocumentViewer - How to customize a report parameter editor in MVC application code example is used to customize the DocumentViewer parameter editor.
See also:
MVC DocumentViewer - How to create a custom CheckedComboBox parameter editor with the "Select All" functionality for a report
ASPxDocumentViewer - How to customize a parameter editor (Creating a multi-select parameter)