myComboBox_SelectedIndexChanged(myComboBox, new EventArgs()); // or (null, null)
Related posts:
How to solve "Response.Redirect cannot be called in a Page callback" for DevExpress Components
Add default value to Devex Grid Columns in C#
ASPxGridView - Disable CheckBox based on condition in GridViewCommandColumn
How to make the default class type 'public' instead of 'internal' in Visual Studio
Passing parameters to JavaScript files