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SpreadsheetControl.CustomAssemblyLoading Event

Occurs before a custom assembly is loaded for use as the Entity Framework data source during mail merge and allows you to cancel the operation.

Namespace: DevExpress.XtraSpreadsheet

Assembly: DevExpress.XtraSpreadsheet.v24.1.dll

NuGet Package: DevExpress.Win.Spreadsheet


public event SpreadsheetCustomAssemblyLoadingEventHandler CustomAssemblyLoading

Event Data

The CustomAssemblyLoading event's data class is SpreadsheetCustomAssemblyLoadingEventArgs. The following properties provide information specific to this event:

Property Description
Cancel Gets or sets a value indicating whether the event should be canceled. Inherited from CancelEventArgs.
ContextName Gets the name of the Entity Framework context.
Handled Gets or sets whether the e.Cancel setting in the event handler makes the final decision on loading the assembly.
Path Gets the path to the external assembly containing the Entity Framework model.


The CustomAssemblyLoading event is raised if the SpreadsheetDataSourceWizardOptions.CustomAssemblyBehavior or the SpreadsheetDataSourceLoadingOptions.CustomAssemblyBehavior property is set to the SpreadsheetCustomAssemblyBehavior.Prompt value.

You can subscribe to the CustomAssemblyLoading event, analyze the SpreadsheetCustomAssemblyLoadingEventArgs.Path string and set the event arguments as follows:

Assignment Meaning
e.Cancel = false Approve the decision to load a custom assembly.
e.Cancel = true Refuse to load a custom assembly.
e.Handled = true The decision is made.
e.Handled = false The decision is not yet made. The service should make the final decision.


using DevExpress.DataAccess.EntityFramework;
using DevExpress.Spreadsheet;
using DevExpress.XtraSpreadsheet.Services;
using System;
using System.Collections.Generic;
using System.Windows.Forms;

namespace MailMergeEFData {
    public partial class Form1 : DevExpress.XtraBars.Ribbon.RibbonForm {
        public Form1() {
            // Handle this event to load a custom data assembly based on a specific condition.
            EFDataSource.BeforeLoadCustomAssemblyGlobal += EFDataSource_BeforeLoadCustomAssemblyGlobal;
            // Prompt for loading a data assembly; default is NeverLoad.
            this.spreadsheetControl1.Options.DataSourceLoading.CustomAssemblyBehavior = DevExpress.XtraSpreadsheet.SpreadsheetCustomAssemblyBehavior.Prompt;
            // Handle this event to decide whether to load a custom data assembly.
            this.spreadsheetControl1.CustomAssemblyLoading += SpreadsheetControl1_CustomAssemblyLoading;
            // The service is employed when loading a template.
            this.spreadsheetControl1.ReplaceService<ICustomAssemblyLoadingNotificationService>(new myCustomAssemblyLoadingNotificationService());

        private void EFDataSource_BeforeLoadCustomAssemblyGlobal(object sender, DevExpress.DataAccess.EntityFramework.BeforeLoadCustomAssemblyEventArgs args) {
            args.AllowLoading = true;

        private void SpreadsheetControl1_CustomAssemblyLoading(object sender, SpreadsheetCustomAssemblyLoadingEventArgs e) {
            // Decide whether to load a custom assembly.
            e.Cancel = MessageBox.Show(String.Format("Do you want to load data from {0}?", e.Path),
                    "CustomAssemblyLoading Event", MessageBoxButtons.YesNo) == DialogResult.No;
            // Decide whether to query the service for the final decision.
            e.Handled = MessageBox.Show(String.Format("Query the service for the final decision?", e.Path),
                    "CustomAssemblyLoading Event", MessageBoxButtons.YesNo) == DialogResult.No; ;

        private void Form1_Load(object sender, EventArgs e) {
            EFDataSource ds = new EFDataSource(new EFConnectionParameters());
            ds.Name = "Contacts";
            ds.ConnectionParameters.CustomAssemblyPath = Application.StartupPath + @"\EFDataModel.dll";
            ds.ConnectionParameters.CustomContextName = "EFDataModel.ContactsEntities";
            ds.ConnectionParameters.ConnectionString = @"Data Source=(LocalDB)\MSSQLLocalDB;attachdbfilename=|DataDirectory|\Contacts.mdf;integrated security=True;";
            this.spreadsheetControl1.Document.MailMergeDataSource = ds;
            this.spreadsheetControl1.Document.MailMergeDataMember = "Customers";            
            this.spreadsheetControl1.Document.Worksheets[0].Cells["A1"].Formula = "=FIELD(\"Company\")";

            try {
                IList<IWorkbook> resultWorkbooks = spreadsheetControl1.Document.GenerateMailMergeDocuments();
                string filename = "SavedDocument0.xlsx";
                resultWorkbooks[0].SaveDocument(filename, DocumentFormat.OpenXml);
            catch (Exception ex) {
                MessageBox.Show(ex.Message, "Exception");

        private void tglShowWizardBrowseButton_CheckedChanged(object sender, DevExpress.XtraBars.ItemClickEventArgs e) {
            // Show the button in the Data Source Wizard to launch the "Browse for assembly" dialog.
            this.spreadsheetControl1.Options.DataSourceWizard.ShowEFWizardBrowseButton = tglShowWizardBrowseButton.Checked;

    public class myCustomAssemblyLoadingNotificationService : ICustomAssemblyLoadingNotificationService {
        public bool RequestApproval(string assemblyPath) {
            return MessageBox.Show(String.Format("Are you sure?\nLoading {0}", assemblyPath),
                "CustomAssemblyLoadingNotificationService", MessageBoxButtons.OKCancel) == DialogResult.OK;
See Also