When and where to use GetType() or typeof()? [duplicate]

typeof is an operator to obtain a type known at compile-time (or at least a generic type parameter). The operand of typeof is always the name of a type or type parameter – never an expression with a value (e.g. a variable). See the C# language specification for more details.

GetType() is a method you call on individual objects, to get the execution-time type of the object.

Note that unless you only want exactly instances of TextBox (rather than instances of subclasses) you’d usually use:

if (myControl is TextBox)
{
    // Whatever
}

Or

TextBox tb = myControl as TextBox;
if (tb != null)
{
    // Use tb
}