按下Messagebox上的帮助按钮时未触发事件

Question

I have a C# app where I'm using Messagebox.Show with a help button, as per Microsoft's example at http://msdn.microsoft.com/en-us/library/szwxe9we.aspx

I add the event to the form, but pressing the help button never fires the event - pressing F1 on the form DOES however. Even taking Microsoft's example almost completely does not fire the event. The whole code is below. Any ideas what I'm not doing?

There is another post where someone had noticed the same.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace WindowsFormsApplication4
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

            DialogResult r = AlertMessageWithCustomHelpWindow();
        }
        // Display a message box with a Help button. Show a custom Help window
        // by handling the HelpRequested event.
        private DialogResult AlertMessageWithCustomHelpWindow()
        {
            // Handle the HelpRequested event for the following message.
            this.HelpRequested += new System.Windows.Forms.HelpEventHandler(this.Form1_HelpRequested);

            this.Tag = "Message with Help button.";

            // Show a message box with OK and Help buttons.
            DialogResult r = MessageBox.Show("Message with Help button.",
                                              "Help Caption", MessageBoxButtons.OK,
                                              MessageBoxIcon.Question,
                                              MessageBoxDefaultButton.Button1,
                                              0, true);

            // Remove the HelpRequested event handler to keep the event
            // from being handled for other message boxes.
            this.HelpRequested -= new System.Windows.Forms.HelpEventHandler(this.Form1_HelpRequested);

            // Return the dialog box result.
            return r;
        }

        private void Form1_HelpRequested (System.Object sender, System.Windows.Forms.HelpEventArgs hlpevent)
        {
            // Create a custom Help window in response to the HelpRequested event.
            Form helpForm = new Form();

            // Set up the form position, size, and title caption.
            helpForm.StartPosition = FormStartPosition.Manual;
            helpForm.Size = new Size(200, 400);
            helpForm.DesktopLocation = new Point(this.DesktopBounds.X +
                                                  this.Size.Width,
                                                  this.DesktopBounds.Top);
            helpForm.Text = "Help Form";

            // Create a label to contain the Help text.
            Label helpLabel = new Label();

            // Add the label to the form and set its text.
            helpForm.Controls.Add(helpLabel);
            helpLabel.Dock = DockStyle.Fill;

            // Use the sender parameter to identify the context of the Help request.
            // The parameter must be cast to the Control type to get the Tag property.
            Control senderControl = sender as Control;

            helpLabel.Text = "Help information shown in response to user action on the '" +
                              (string)senderControl.Tag + "' message.";

            // Set the Help form to be owned by the main form. This helps
            // to ensure that the Help form is disposed of.
            this.AddOwnedForm(helpForm);

            // Show the custom Help window.
            helpForm.Show();

            // Indicate that the HelpRequested event is handled.
            hlpevent.Handled = true;

        }


    }
}

Answer 1

Take the line

DialogResult r = AlertMessageWithCustomHelpWindow();

out of the Form1 constructor - maybe put it in a button click handler on the main form. It looks like you're blocking the UI thread with MessageBox.Show() stopping the help dialog displaying.