how can i set focus on textbox control in c# windows forms application if button have error?

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C#

ASP.NET

Hi friends!


i want to set focus on my textbox control i used focus() method but it is not working.

set focus on id field
ex.

database id = 5
uer enter on id textbox = 5;

5 is already exist so user can again set focus on idtextbox. and not showing error about primary key and foreign key