Hi,
your 'certain condition' is a little vague. Which event is used is up to your condition. Is it TextChanged or just a timer... ? Change the text and disable the column is easy, you can set the relative property, say Text property or Visible property.
For example if column a is greater than column b, or some other formula.
Hi,
As I said, when to check the condition is all up to you. You may check it after the data is loaded or updated everytime.
Because your conditions are related to your business rules, you'd better not hard-code the rules. Write the rules in another file, therefore you have more flexibility.