c# - Support progress bar in Mdi parent form to display child form -

i working on application has mdi parent child form.

i have 4 forms in when clicking on second form's button , loading third form user login page, it's loading slow.as username has read data database , display availabe name in username combobox.

so want show progressbar till list of usernames extracted..and progress bar ends third form displayed.

please suggests how can implement this.