I guess you are trying to add RadPanelItem on OnRowSelected event of RadGrid. The issue you are facing is clicking on Radbutton inside RadPane, it lost all the controls created dynamically.
This is because the controls which is created dynamically(from code behind) should not persist after a postback. Please, note that ASP.NET do not recreate the dynamic controls and you should recreate them in a suitable event according to your needs.
I hope this information helps. Please let me know if you need more help.
but if I want to change the parameters in the controls - like textbox.text,
he don't do it.
after I build the controls in panelbaritem on page_load
I click on some row in radgrid and he build the controls again,
but now after postback he show me the controls but I can't find them in the code.
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
I have created a similar scenario( created a TextBox dynamically, added it on RadPanelItem and accessing that TextBox on external RadButton OnClick event). Please have a look into the following code snippet and let me know if you need help.
Unfortunately I couldn't replicate the issue at my end. Please provide your full code so that I can replicate the issue. I have noticed that the given code will cause an error, if we use 'Text' property instead of 'text ' for setting the text.