TdxBackendCustomParameter.AllowNull Property

Specifies whether Null can be assigned as the Report or Dashboard parameter value.

Declaration

property AllowNull: Boolean read; write; default False;

Property Value

Type	Default	Description
Boolean	False	False Default. An empty field is treated as an empty string. True An empty field is treated as Null.

Remarks

Set the AllowNull property to True to treat an empty field as a Null Variant. Otherwise, an empty field is interpreted as an empty string or an empty array for multi-value parameters.

This property corresponds to the Allow null value option in the Report Designer or the Allow Null option in the Dashboard Designer:

Report

Dashboard

Code Examples

The following code snippets allow users to specify an empty string as the parameter value.

Note

The AllowNull property is common to report and dashboard parameters. These examples perform the same operation but use component-specific APIs.

Allow Null Value in Report Parameters

Delphi

uses
  dxReport.Control;   // Declares the TdxReportControl class

procedure TForm1.cxButton1Click(Sender: TObject);
begin
  dxReportControl1.Parameters['countryParameter'].AllowNull := True;
end;

C++

#include "dxReport.Control.hpp"   // Declares the TdxReportControl class

// Add the following linker directives to the corresponding CPP source file:
#pragma link "dxReport.Control"   // Required to use dxReport.Control.hpp declarations

void __fastcall TForm1::cxButton1Click(TObject *Sender)
{
  dxReportControl1->Parameters[L"countryParameter"]->AllowNull = true;
}

Allow Null Value in Dashboard Parameters

Delphi

uses
  dxDashboard.Control;   // Declares the TdxDashboardControl class

procedure TForm1.cxButton1Click(Sender: TObject);
begin
  dxDashboardControl1.Parameters['countryParameter'].AllowNull := True;
end;

C++

#include "dxDashboard.Control.hpp";   // Declares the TdxDashboardControl class

// Add the following linker directives to the corresponding CPP source file:
#pragma link "dxDashboard.Control"   // Required to use dxDashboard.Control.hpp declarations

void __fastcall TForm1::cxButton1Click(TObject *Sender)
{
  dxDashboardControl1->Parameters[L"countryParameter"]->AllowNull = true;
}