editable dropdown control

Hello, Muhammad,      
  
If I understand your requirement correctly, you need to allow editing the text in the PropertyGridDropDownListEditor. For this purpose, it is necessary to handle the EditorInitialized event and set the DropDownStyle property to DropDown. 

  
If it is not the exact requirement, please specify in details what is the exact requirement that you are trying to achieve. Thus, we would be able to get better understanding of the precise case and think about a suitable solution.

I hope this information helps. 

Regards,
Dess | Tech Support Engineer, Sr.
Progress Telerik

i have set the dropdown . but the input value don't take effect. do you know why?

Hello, Steve,

Note that the PropertyGridDropDownListEditor accepts only valid values considering the items available in the applied DataSource to the editor. 

According to the provided gif file it seems that you type in the editable area "D" and "E" which don't exist in the DataSource collection. That is why they are not kept. If you type "C" for example, it is expected to be stored in the property item. 

However, if your requirement is to allow the end-users to enter free input, it has to be added to the DataSource as a valid item. The following help article demonstrates a sample approach for the drop down editor in RadGridView. In a similar way, this custom behavior can be achieved for RadPropertyGrid as well: https://docs.telerik.com/devtools/winforms/controls/gridview/editors/how-to/allow-end-users-to-add-items-to-dropdownlisteditor 

I hope this information helps. If you need any further assistance please don't hesitate to contact me. 

Regards,
Dess | Tech Support Engineer, Sr.
Progress Telerik