ChartCalculatedField.Expression Property

Gets or sets an expression the calculated field uses to evaluate its values.

Namespace: DevExpress.Xpf.Charts

Assembly: DevExpress.Xpf.Charts.v24.1.dll

NuGet Package: DevExpress.Wpf.Charts

Declaration

C#

public string Expression { get; set; }

VB.NET

Public Property Expression As String

Property Value

Type	Description
String	A string that represents an expression written in Criteria Language.

Example

The following example shows how to create a calculated field and then use this field as a data source for a series. The field’s values are calculated by the following expression: [Time.Seconds] * [Velocity].

XAML

<dxc:ChartControl x:Name="chartControl">
    <dxc:ChartControl.DataContext>
        <local:ChartViewModel/>
    </dxc:ChartControl.DataContext>
    <dxc:ChartControl.CalculatedFields>
        <dxc:ChartCalculatedField FieldName="Displacement" 
                                  Expression="[Time.Seconds] * [Velocity]" 
                                  FieldType="Double"/>
    </dxc:ChartControl.CalculatedFields>
    <dxc:XYDiagram2D>
        <dxc:SplineSeries2D DisplayName="Series" 
                            DataSource="{Binding DataPoints}"
                            ArgumentDataMember="Time"
                            ValueDataMember="Displacement" 
                            CrosshairLabelPattern="{}{Displacement:f1}" 
                            MarkerVisible="True"/>
        ...
    </dxc:XYDiagram2D>
</dxc:ChartControl>

C#

using System;
using System.Collections.Generic;
using System.Windows;

namespace CalculatedFields {
    public class ChartViewModel {
        List<DataPoint> dataPoints;
        public List<DataPoint> DataPoints {
            get {
                if (dataPoints == null) {
                    dataPoints = new List<DataPoint> {
                            new DataPoint (new TimeSpan(0, 0, 0), 10),
                            new DataPoint (new TimeSpan(0, 0, 1), 11.46),
                            new DataPoint (new TimeSpan(0, 0, 2), 11.90),
                            new DataPoint (new TimeSpan(0, 0, 3), 12.1),
                            new DataPoint (new TimeSpan(0, 0, 4), 12.236),
                            new DataPoint (new TimeSpan(0, 0, 5), 12.325),
                            new DataPoint (new TimeSpan(0, 0, 6), 12.625),
                            new DataPoint (new TimeSpan(0, 0, 7), 13.896),
                            new DataPoint (new TimeSpan(0, 0, 8), 14.123),
                            new DataPoint (new TimeSpan(0, 0, 9), 14.623),
                            new DataPoint (new TimeSpan(0, 0, 10), 15.007),
                            new DataPoint (new TimeSpan(0, 0, 11), 15.452),
                            new DataPoint (new TimeSpan(0, 0, 12), 15.756)
                };
                }
                return dataPoints;
            }
        }
    }
    public class DataPoint {
        public TimeSpan Time { get; set; }
        public double Velocity { get; set; }
        public DataPoint(TimeSpan time, double velocity) {
            this.Time = time;
            this.Velocity = velocity;
        }
    }
}

VB.NET

Imports System
Imports System.Collections.Generic
Imports System.Windows

Namespace CalculatedFields
    Public Class ChartViewModel
        Private f_DataPoints As List(Of DataPoint)
        Public ReadOnly Property DataPoints As List(Of DataPoint)
            Get
                If f_DataPoints Is Nothing Then
                    f_DataPoints = New List(Of DataPoint) From {
                        New DataPoint(New TimeSpan(0, 0, 0), 10),
                        New DataPoint(New TimeSpan(0, 0, 1), 11.46),
                        New DataPoint(New TimeSpan(0, 0, 2), 11.90),
                        New DataPoint(New TimeSpan(0, 0, 3), 12.1),
                        New DataPoint(New TimeSpan(0, 0, 4), 12.236),
                        New DataPoint(New TimeSpan(0, 0, 5), 12.325),
                        New DataPoint(New TimeSpan(0, 0, 6), 12.625),
                        New DataPoint(New TimeSpan(0, 0, 7), 13.896),
                        New DataPoint(New TimeSpan(0, 0, 8), 14.123),
                        New DataPoint(New TimeSpan(0, 0, 9), 14.623),
                        New DataPoint(New TimeSpan(0, 0, 10), 15.007),
                        New DataPoint(New TimeSpan(0, 0, 11), 15.452),
                        New DataPoint(New TimeSpan(0, 0, 12), 15.756)
                    }
                End If
                Return f_DataPoints
            End Get
        End Property
    End Class
    Public Class DataPoint
        Public Property Time As TimeSpan
        Public Property Velocity As Double
        Public Sub New(ByVal time As TimeSpan, ByVal velocity As Double)
            Me.Time = time
            Me.Velocity = velocity
        End Sub
    End Class
End Namespace