Hi Piotr Grzywa,
Thanks for contacting Syncfusion support.
We have checked your requirement about doing serialization and de-serialization an object in SplitContainerAdv control and prepared sample which tries to meet your requirement. In this sample, we have done StatePersistence for SplitterDistance and SplitterBackColor properties in SplitContainerAdv control in XML file format, like this you can do state persistence in other formats also. Please download the sample for the same from below location,
If we have misunderstood your query please get back to us with more details. This would help us to provide solution at earliest.
Regards,
Durga S.