Pass System.Nullable Arguments

The example uses the NetDocNullable assembly to show how to call a method with a System.Nullable input argument. It uses the MATLAB^® plot function to show how to handle a System.Nullable output argument.

Suppose that you have this C# signature for the SetField method that has System.Nullable parameters.

public Nullable<double> SetField(Nullable<double> db)

The function signature in MATLAB is:

Return Type	Name	Arguments
System.Nullable <System*Double> RetVal	SetField	(NetDocNullable. MyClass this, System.Nullable <System*Double> db)

For an example, build the NetDocNullable assembly from this C# source code using the directions in Build and Load .NET Assembly for MATLAB. NetDocNullable defines method SetField which has System.Nullable arguments.

using System;

namespace NetDocNullable
{
    public class MyClass
    {
        private Nullable<double> myField = null;

        public Nullable<double> GetField()
        {
            return myField;
        }
        public Nullable<double> SetField(Nullable<double> db)
        {
            myField = db;
            return myField;
        }
    }
}

Create a mlClass variable to call SetField. MATLAB automatically converts double and null values to System.Nullable<System*Double> objects.

mlClass = NetDocNullable.MyClass;

Call SetField with a double value.

field1 = SetField(mlClass,10)

field1 = 
  System.Nullable<System*Double>
  Package: System

  Properties:
    HasValue: 1
       Value: 10
  Methods, Superclasses

The HasValue property is true (1) and the Value property is 10.

Pass null value [].

field2 = SetField(mlClass,[])

field2 = 
  System.Nullable<System*Double>
  Package: System

  Properties:
    HasValue: 0
  Methods, Superclasses

The HasValue property is false (0), and it has no Value property.

Pass System.Nullable Argument to SetField Method

Suppose that you have this C# signature for the SetField method that has System.Nullable parameters.

public Nullable<double> SetField(Nullable<double> db)

The function signature in MATLAB is:

Return Type	Name	Arguments
System.Nullable <System*Double> RetVal	SetField	(NetDocNullable. MyClass this, System.Nullable <System*Double> db)

To run the example, build the NetDocNullable assembly from this C# source code using the directions in Build and Load .NET Assembly for MATLAB. NetDocNullable defines method SetField which has System.Nullable arguments.

using System;

namespace NetDocNullable
{
    public class MyClass
    {
        private Nullable<double> myField = null;

        public Nullable<double> GetField()
        {
            return myField;
        }
        public Nullable<double> SetField(Nullable<double> db)
        {
            myField = db;
            return myField;
        }
    }
}

Create a mlClass variable to call SetField. MATLAB automatically converts double and null values to System.Nullable<System*Double> objects.

mlClass = NetDocNullable.MyClass;

Call SetField with a double value.

field1 = SetField(mlClass,10)

field1 = 
  System.Nullable<System*Double>
  Package: System

  Properties:
    HasValue: 1
       Value: 10
  Methods, Superclasses

The HasValue property is true (1) and the Value property is 10.

Pass null value [].

field2 = SetField(mlClass,[])

field2 = 
  System.Nullable<System*Double>
  Package: System

  Properties:
    HasValue: 0
  Methods, Superclasses

The HasValue property is false (0), and it has no Value property.

Handle System.Nullable Output Arguments in MATLAB

Before you use a System.Nullable object in MATLAB, first decide how to handle null values. If you ignore null values, you might get unexpected results when you use the value in a MATLAB function.

The System.Nullable class provides two techniques for handling null values. To provide special handling for null values, use the HasValue property. To treat a null value in the same way as a double, use the GetValueOrDefault method.

Create a MATLAB function, plotValue.m, which detects null values and treats them differently from numeric values. The input is a System.Nullable<System*Double> type. If the input is null, the function displays a message. If the input value is double, it creates a line graph from 0 to the value.

function plotValue(x)
% x is System.Nullable<System*Double> type
if (x.HasValue && isfloat(x.Value))
  plot([0 x.Value])
else
  disp("No Data")
end

The plotValue function uses the HasValue property of the input argument to detect null values and calls the MATLAB plot function using the Value property.

Call plotValue with variable field1 to display a line graph.

plotValue(field1)

Call plotValue with the variable field2, a null value.

plotValue(field2)

No Data

If you do not need special processing for null values, use the GetValueOrDefault method. To display the GetValueOrDefault function signature, type:

methodsview(field1)

Look for the GetValueOrDefault function signature:

Name	Return Type	Arguments
GetValueOrDefault	double scalar RetVal	(System.Nullable <System*Double> this)

This method converts the input variable to double so you can directly call the MATLAB plot function:

myData = GetValueOrDefault(field1);
plot([0 myData+2])

The GetValueOrDefault method converts a null value to the default numeric value, 0.

defaultData = GetValueOrDefault(field2)

defaultData =
     0

Call plot:

plot([0 defaultData])

You can change the default value using the GetValueOrDefault method. Open the methodsview window and look for the GetValueOrDefault function signature:

Name	Return Type	Arguments
GetValueOrDefault	double scalar RetVal	(System.Nullable <System*Double> this, double scalar defaultValue)

Set the defaultValue input argument to a new value, -1, and plot the results for null value field2.

defaultData = GetValueOrDefault(field2,-1);
plot([0 defaultData])