how to set a filter that expression term generated dynamictly?

[John]

I drag a TextBox named textboxA and a Table that fields some data in my reporting page, I want to set a filter that expression term are generated dynamictly, for example, I input the value in the textboxA then I set the filter property of the table like 
        Fields.XXXX = textboxA.Value or textboxname(of the table).Value = textboxA.Value
Above methods are illegal or useless, is anyone know how to do like this!?