How to use a simple YES/NO MessageBox in a SharePoint 2010 EventHandler?

I've created an Eventhandler (SPEventReceiverType.ItemDeleting) which is called when a user is deleting an SPListItem from a specific SPList. For every item theres an website and I want to simple ask the user with a yes/no-MessageBox if it should delete the site as well... And there is the problem, after quite some time on google, I realized that I couldn't find some usuful hints how to show a MessageBox, and if clicked Yes, how to continue doing some other code.

Anyway, the usual way I would do this, doesn't works in a SharePoint 2010 EventHandler:

if (MessageBox.Show("Do you want to delete the site as well?", "Delete?", 
    MessageBoxButtons.YesNo, MessageBoxIcon.Question) == DialogResult.Yes)
{
    /开发者_开发技巧/ Continue Here if "Yes" has been clicked
}

Sometimes, SharePoint is driving me nuts. sincerely, Markus Schwalbe

P.S. If you like, you can try to solve my other question :)

---

You can do something like this:

public override void ItemDeleting(SPItemEventProperties properties)
        {

            string updateID = Convert.ToString(properties.ListItem["ID"], CultureInfo.InvariantCulture);
            string itemUID = tmpItem.UniqueId.ToString();
            string urlProcessing = string.Format(CultureInfo.InvariantCulture, Constants.StringRedirect, web.Url, Constants.PersonRecord, "Processing.aspx", itemUID, updateID, modifyTime);
            properties.Status = SPEventReceiverStatus.CancelNoError;
            SPUtility.Redirect(urlProcessing, SPRedirectFlags.Static, this.currentContext);

    }

Processing.aspx will contain a custom MessageBox webPart which will either delete the item or not depending on the response. It will read the ID from Url query string. Here is snippet:

using System;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.Globalization;
using System.Runtime.InteropServices;
using System.Security.Permissions;
using System.Text;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using Microsoft.SharePoint;
using Microsoft.SharePoint.Utilities;


/// <summary>
/// This class contains operations to check if a username is duplicated or not
/// </summary>  
[Guid("ddeaa4a4-6d63-4fc8-9a17-8874db582388")]
[SecurityPermission(SecurityAction.LinkDemand, Unrestricted = true)]
[SecurityPermission(SecurityAction.InheritanceDemand, Unrestricted = true)]
[CLSCompliant(false)]
public class ConfirmWebpart : Microsoft.SharePoint.WebPartPages.WebPart
{
    /// <summary>
    /// Duplicated username
    /// </summary>
    private string userName;

    /// <summary>
    /// UNID of a item
    /// </summary>
    private string itemID;

    /// <summary>
    /// ID of updating item
    /// </summary>
    private string updateID;

    /// <summary>
    /// Last edit time
    /// </summary>
    private string lastEdit;

    /// <summary>
    /// To check error in the application.  
    /// </summary>
    private bool error;

    /// <summary>
    /// Current context
    /// </summary>
    private HttpContext currentContext;

    /// <summary>
    /// Initializes a new instance of the ConfirmWebpart class.
    /// </summary>
    public ConfirmWebpart()
    {
        this.currentContext = HttpContext.Current;
        this.ExportMode = WebPartExportMode.All;
    }

    /// <summary>
    /// Ensures that the CreateChildControls() is called before events.
    /// Use CreateChildControls() to create your controls.
    /// </summary>
    /// <param name="e">e parameter</param>
    [SuppressMessage("Microsoft.Security", "CA2109:ReviewVisibleEventHandlers", Justification = "This is to catch all possible exceptions and to prevent exceptions to bubble up on screen.")]
    protected override void OnLoad(EventArgs e)
    {
        if (!this.error)
        {
            try
            {
                base.OnLoad(e);
             this.EnsureChildControls();
            }
            catch (Exception ex)
            {
                this.HandleException(ex);
                throw;
            }
        }
    }

    /// <summary>
    /// Create all your controls here for rendering.
    /// Try to avoid using the RenderWebPart() method.
    /// </summary>
    protected override void CreateChildControls()
    {
        if (!this.error)
        {
            try
            {
                base.CreateChildControls();
                this.GetQueryStringValues();
                this.RenderContents();
            }
            catch (Exception ex)
            {
                this.HandleException(ex);
                throw;
            }
        }
    }

    /// <summary>
    /// Clear all child controls and add an error message for display.
    /// </summary>
    /// <param name="ex">ex parameter</param>
    protected void HandleException(Exception ex)
    {
        this.error = true;
        this.Controls.Clear();
        this.Controls.Add(new LiteralControl(ex.Message));
    }

    /// <summary>
    /// Get all querystring value and assign to private members
    /// </summary>
    protected void GetQueryStringValues()
    {
        this.itemID = Page.Request.QueryString[Constants.ItemD];
        this.updateID = Page.Request.QueryString[Constants.Update];
        this.lastEdit = Page.Request.QueryString[Constants.LastEdit];
    }

    /// <summary>
    /// Render UI form
    /// </summary>
    protected void RenderContents()
    {
        this.GetDuplicatedUserName();

        this.Controls.Add(new LiteralControl("<table cellpadding=\"0\" cellspacing=\"0\"><tr style=\"height:50px\"><td style=\"width:50px\"></td><td colspan=\"3\"></td></tr><tr style=\"font-size: medium;color: #3366FF;height:40px\"><td></td><td colspan=\"3\">"));
        this.Controls.Add(new LiteralControl(string.Format(CultureInfo.CurrentCulture, Constants.ConfirmMessage, this.userName)));
        this.Controls.Add(new LiteralControl("</tr><tr><td></td><td colspan=\"3\"></td></tr><tr><td style=\"color: #3366FF\"></td><td colspan=\"3\" style=\"color: #3366FF\">"));
        this.Controls.Add(new LiteralControl(Constants.YesAction));
        this.Controls.Add(new LiteralControl("</tr><tr><td style=\"color: #3366FF\"></td><td colspan=\"3\" style=\"color: #3366FF\">"));
        this.Controls.Add(new LiteralControl(Constants.NoAction));
        this.Controls.Add(new LiteralControl("</td></tr><tr><td></td><td colspan=\"3\" style=\"height:20px\"></td></tr><tr><td style=\"width:100px\"></td><td style=\"width:100px\"></td><td>"));

        //// Add Yess button
        Button btnYes = new Button();
        btnYes.Text = Constants.YesButtonLabel;
        btnYes.Width = new Unit(70);
        btnYes.Click += new EventHandler(this.BtnYesClick);
        this.Controls.Add(btnYes);

        this.Controls.Add(new LiteralControl("</td><td>"));
        //// Add No button
        Button btnNo = new Button();
        btnNo.Text = Constants.NoButtonLabel;
        btnNo.Click += new EventHandler(this.BtnNoClick);
        btnNo.Width = new Unit(70);
        this.Controls.Add(btnNo);
        this.Controls.Add(new LiteralControl("</td></tr></table>"));
    }



    /// <summary>
    /// This method is used to handle the click event of Yes button
    /// </summary>
    /// <param name="sender">sender parameter</param>
    /// <param name="e">argument parameter</param>
    private void BtnYesClick(object sender, EventArgs e)
    {
       //Delete the item
    }

    /// <summary>
    /// This method is used to handle the click event of No button
    /// </summary>
    /// <param name="sender">sender parameter</param>
    /// <param name="e">argument parameter</param>
    private void BtnNoClick(object sender, EventArgs e)
    {
        // Redirect to the default view of People list
        string defaultView = string.Format(CultureInfo.InvariantCulture, Constants.WebRedirectUrl, SPContext.Current.Web.Url, Constants.ListName);
        SPUtility.Redirect(defaultView, SPRedirectFlags.Trusted, this.currentContext);
    }

}

---

The YES/NO confirmation you are trying to do, should be handled before it even gets to the event receiver. If for example, i was deleting the item from a scheduled job, or from powershell, or from a content deployment import/export, there is no way i can capture user input. Worse case the process blocks forever waiting for user input that never comes.

The SPEventReceiverType.ItemDeleting event should be used, for example, to validate a delete based on information in the site (eg stop deleting referenced data in a lookup field) and if it fails, then use the properties to cancel it.

properties.Cancel = true; 
properties.ErrorMessage = "Can not delete";