c# - Validating Text boxes and drop down lists -

i working on visual studio asp.net website , have web aspx page textboxes drop down lists, , submit button @ bottom of page. want submit button not function unless text boxes filled , selection drop down menu made...how can easiest way possible? have tried using required field validators , done research still cant seem achieve this... great!

i use textbox validation angular , javascript integrate asp.net project. angular can use ng-disabled disabled button it's easy.