You can validate data by handling Property Validating event which is raised by Rad Property Grid when the current item changes or when the item loses input focus (when pressing the The code snippet below demonstrates simple data validation scenario.
It is performed on a string property to do not allow entering an empty string.
I further know that I could decorate my object with attributes - but the reason to use your Property Grid is that the object is large (a lot of properties) and I don't want to define all these things.
Last not least I implemented "Is Valid" like in the following snippet.
Data validation settings are located on the Data tab in the Data Tools group.