[SOLVED] Managing null values in variants using Delphi

Managing null values in variants using Delphi

I'm working with a COM component which exposes a lot of Variant properties, but sometimes these values are null. When I try to convert these values to string (or another Delphi type) the application raises an exception like this:

Could not convert variant of type (Null) into type (String)

But if I use .net to call the same properties and the values are null, no exceptions are raised and the null values are treated as empty strings.

My question there is a way to handle these null values from Delphi avoiding these exceptions?

Thanks in advance.

Solution

Try setting NullStrictConvert to False.

As it's a global variable I use it like follows to minimize side effects:

var
  OldNullStrictConvert: Boolean;
begin
  OldNullStrictConvert := NullStrictConvert;
  NullStrictConvert := False;
  try
    // code containing conversions
  finally
    NullStrictConvert := OldNullStrictConvert;
  end;
end;

(In reality I have made a guardian interface out of this.)

NB: Where it's feasible I prefer code like Warren's.