TParam.IsNull Property

Indicates whether the value assigned to the parameter is NULL (blank).

Pascal

property IsNull: Boolean;

C++

__property Boolean IsNull;

Description

Inspect IsNull to discover if the value of the parameter is NULL, indicating the value of a blank field. NULL values can arise in the following ways:

Assigning the value of another, NULL, parameter.

Assigning the value of a blank field.

Calling the Clear method.

Note: NULL parameters are not the same as unbound parameters. Unbound parameters have not had a value assigned. NULL parameters have a NULL value. NULL parameters may be bound or unbound.

C++ Examples:

Copy Code

/*
This example requires a TClientDataSet and a button on a form.
*/
void __fastcall TForm1::Button1Click(TObject *Sender)
{
for (int I = 0; I < CDS->Params->Count; I++)
{
  if (CDS->Params->Items[I]->IsNull &&
      CDS->Params->Items[I]->DataType == ftInteger)
    CDS->Params->Items[I]->AsInteger = -1;
}}

void __fastcall TForm1::FormCreate(TObject *Sender)
{
  CDS->LoadFromFile(GetCurrentDir() + L"/../CDS.XML");
  CDS->Params->CreateParam(ftInteger, "StateParam", ptInput);
  CDS->Params->CreateParam(ftInteger, "MyParam", ptInput);
}

Delphi Examples:

Copy Code

{
This example requires a TClientDataSet and a button on a form.
}
{$IFNDEF UNICODE}
uses SwSystem;
{$ENDIF}

procedure TForm1.Button1Click(Sender: TObject);
var
  I : Integer;
begin
{ Assign -1 to any integer parameter which does not have a value. }
for I := 0 to CDS.Params.Count - 1 do
  if (CDS.Params.Items[I].IsNull) and
     (CDS.Params.Items[I].DataType = ftInteger) then
    { Items is the default property, so you can omit its name }
    CDS.Params[I].AsInteger := -1;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
{$IFDEF UNICODE}
  CDS.LoadFromFile(GetCurrentDir + '\CDS.XML');
{$ELSE}
  CDS.LoadFromFile(gsAppPath + 'CDS.XML');
{$ENDIF}
  CDS.Params.CreateParam(ftInteger, 'StateParam', ptInput);
  CDS.Params.CreateParam(ftInteger, 'MyParam', ptInput);
end;