How to: Pass a Dashboard Parameter to a Calculated Field's Expression in Code

• Aug 01, 2019
• 2 minutes to read

The following example demonstrates how to create a new dashboard parameter and pass it to a calculated field’s expression.

In this example, the dashboard connects to the Northwind database and selects data from the ‘SalesPerson’ table. A new calculated field evaluated at a summary level returns ‘true’ or ‘false’ depending on whether on not the average discount exceeds the selected parameter value.

Note

A complete sample project is available at https://github.com/DevExpress-Examples/how-to-pass-a-dashboard-parameter-to-a-calculated-fields-expression-in-code-e5135.

Form1.cs

using DevExpress.XtraEditors;
using DevExpress.DashboardCommon;
using DevExpress.DataAccess.ConnectionParameters;

namespace Dashboard_ParametersAndCalculatedFileds {
    public partial class Form1 : XtraForm {
        public Form1() {
            InitializeComponent();

            Dashboard dashboard = new Dashboard();
            dashboard.LoadFromXml(@"..\..\Data\Dashboard.xml");
            DashboardSqlDataSource dataSource = (DashboardSqlDataSource)dashboard.DataSources[0];
            GridDashboardItem grid = (GridDashboardItem)dashboard.Items[0];

            // Creates a new dashboard parameter.
            StaticListLookUpSettings settings = new StaticListLookUpSettings();
            settings.Values = new string[] { "0.01", "0.05", "0.1" };
            DashboardParameter discountValue = new DashboardParameter("discountValue", 
                typeof(double), 0.05, "Select discount:", true, settings);
            dashboard.Parameters.Add(discountValue);

            // Creates a new calculated field and passes the created dashboard parameter 
            // to a calculated field expression.
            CalculatedField isGreater = new CalculatedField();
            isGreater.DataMember = "SalesPerson";
            isGreater.Name = "IsGreater";
            isGreater.Expression = "ToStr(Iif(Avg([Discount]) >= [Parameters.discountValue], 'TRUE', 'FALSE'))";
            dataSource.CalculatedFields.Add(isGreater);

            grid.Columns.Add(new GridMeasureColumn(new Measure("IsGreater")));
            dashboardViewer1.Dashboard = dashboard;
        }
    }
}

Form1.vb

Imports DevExpress.XtraEditors
Imports DevExpress.DashboardCommon
Imports DevExpress.DataAccess.ConnectionParameters

Namespace Dashboard_ParametersAndCalculatedFileds
    Partial Public Class Form1
        Inherits XtraForm

        Public Sub New()
            InitializeComponent()

            Dim dashboard As New Dashboard()
            dashboard.LoadFromXml("..\..\Data\Dashboard.xml")
            Dim dataSource As DashboardSqlDataSource = CType(dashboard.DataSources(0), DashboardSqlDataSource)
            Dim grid As GridDashboardItem = CType(dashboard.Items(0), GridDashboardItem)

            ' Creates a new dashboard parameter.
            Dim settings As New StaticListLookUpSettings()
            settings.Values = New String() { "0.01", "0.05", "0.1" }
            Dim discountValue As New DashboardParameter("discountValue", GetType(Double), 0.05, _
                                                        "Select discount:", True, settings)
            dashboard.Parameters.Add(discountValue)

            ' Creates a new calculated field and passes the created dashboard parameter 
            ' to a calculated field expression.
            Dim isGreater As New CalculatedField()
            isGreater.DataMember = "SalesPerson"
            isGreater.Name = "IsGreater"
            isGreater.Expression = "ToStr(Iif(Avg([Discount]) >= [Parameters.discountValue], 'TRUE', 'FALSE'))"
            dataSource.CalculatedFields.Add(isGreater)

            grid.Columns.Add(New GridMeasureColumn(New Measure("IsGreater")))
            dashboardViewer1.Dashboard = dashboard
        End Sub
    End Class
End Namespace