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HelpEventHandler Delegate

Represents the method that will handle the HelpRequested event of a Control.

[Visual Basic]
<Serializable>
Public Delegate Sub HelpEventHandler( _
   ByVal sender As Object, _
   ByVal hlpevent As HelpEventArgs _
)
[C#]
[Serializable]
public delegate void HelpEventHandler(
   object sender,
   HelpEventArgs hlpevent
);
[C++]
[Serializable]
public __gc __delegate void HelpEventHandler(
   Object* sender,
   HelpEventArgs* hlpevent
);

[JScript] In JScript, you can use the delegates in the .NET Framework, but you cannot define your own.

Parameters [Visual Basic, C#, C++]

The declaration of your event handler must have the same parameters as the HelpEventHandler delegate declaration.

sender
The source of the event.
hlpevent
A HelpEventArgs that contains the event data.

Remarks

When you create a HelpEventHandler delegate, you identify the method that will handle the event. To associate the event with your event handler, add an instance of the delegate to the event. The event handler is called whenever the event occurs, unless you remove the delegate. For more information about handling events with delegates, see Events and Delegates.

Example

[Visual Basic, C#, C++] The following example demonstrates handling the HelpRequested event to display custom Help content on a form containing four address fields. The HelpRequested event is raised either by pressing the F1 key with the focus in an address field, or by the using the context-sensitive Help button and clicking the Help cursor on an address field. The Handled property is set to true to indicate that the HelpRequested event is handled. The example also demonstrates storing the Help text in the Control.Tag property.

[Visual Basic] 
Imports System
Imports System.Drawing
Imports System.Windows.Forms

Public Class Form1
    Inherits System.Windows.Forms.Form
    Private WithEvents addressTextBox As System.Windows.Forms.TextBox
    Private WithEvents label2 As System.Windows.Forms.Label
    Private WithEvents cityTextBox As System.Windows.Forms.TextBox
    Private WithEvents label3 As System.Windows.Forms.Label
    Private WithEvents stateTextBox As System.Windows.Forms.TextBox
    Private WithEvents zipTextBox As System.Windows.Forms.TextBox
    Private WithEvents helpLabel As System.Windows.Forms.Label

    <STAThread()> _
    Shared Sub Main()
        Application.Run(New Form1)
    End Sub 'Main

    Public Sub New()
        Me.addressTextBox = New System.Windows.Forms.TextBox
        Me.helpLabel = New System.Windows.Forms.Label
        Me.label2 = New System.Windows.Forms.Label
        Me.cityTextBox = New System.Windows.Forms.TextBox
        Me.label3 = New System.Windows.Forms.Label
        Me.stateTextBox = New System.Windows.Forms.TextBox
        Me.zipTextBox = New System.Windows.Forms.TextBox

        ' Help Label
        Me.helpLabel.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D
        Me.helpLabel.Location = New System.Drawing.Point(8, 80)
        Me.helpLabel.Size = New System.Drawing.Size(272, 72)
        Me.helpLabel.Text = "Click on any control to give it focus, and then " & _
            "press F1 to display help for that" + " control.  Alternately, you can " & _
            "click the help button at the top of the dialog and then click on a control."

        ' Address Label
        Me.label2.Location = New System.Drawing.Point(16, 8)
        Me.label2.Size = New System.Drawing.Size(100, 16)
        Me.label2.Text = "Address:"

        ' Comma Label
        Me.label3.Location = New System.Drawing.Point(136, 56)
        Me.label3.Size = New System.Drawing.Size(16, 16)
        Me.label3.Text = ","

        ' Address TextBox
        Me.addressTextBox.Location = New System.Drawing.Point(16, 24)
        Me.addressTextBox.Size = New System.Drawing.Size(264, 20)
        Me.addressTextBox.TabIndex = 0
        Me.addressTextBox.Tag = "Enter the stree address in this text box."
        Me.addressTextBox.Text = ""

        ' City TextBox
        Me.cityTextBox.Location = New System.Drawing.Point(16, 48)
        Me.cityTextBox.Size = New System.Drawing.Size(120, 20)
        Me.cityTextBox.TabIndex = 3
        Me.cityTextBox.Tag = "Enter the city here."
        Me.cityTextBox.Text = ""

        ' State TextBox
        Me.stateTextBox.Location = New System.Drawing.Point(152, 48)
        Me.stateTextBox.MaxLength = 2
        Me.stateTextBox.Size = New System.Drawing.Size(32, 20)
        Me.stateTextBox.TabIndex = 5
        Me.stateTextBox.Tag = "Enter the state in this text box."
        Me.stateTextBox.Text = ""

        ' Zip TextBox
        Me.zipTextBox.Location = New System.Drawing.Point(192, 48)
        Me.zipTextBox.Size = New System.Drawing.Size(88, 20)
        Me.zipTextBox.TabIndex = 6
        Me.zipTextBox.Tag = "Enter the zip code here."
        Me.zipTextBox.Text = ""

        ' Set up how the form should be displayed and add the controls to the form.
        Me.ClientSize = New System.Drawing.Size(292, 160)
        Me.Controls.AddRange(New System.Windows.Forms.Control() {Me.zipTextBox, _
                                Me.stateTextBox, Me.label3, Me.cityTextBox, _
                                Me.label2, Me.helpLabel, Me.addressTextBox})
        Me.FormBorderStyle = System.Windows.Forms.FormBorderStyle.FixedDialog
        Me.HelpButton = True
        Me.MaximizeBox = False
        Me.MinimizeBox = False
        Me.Text = "Help Event Demonstration"
    End Sub 'New

    Private Sub textBox_HelpRequested(ByVal sender As Object, ByVal hlpevent As System.Windows.Forms.HelpEventArgs) Handles addressTextBox.HelpRequested, cityTextBox.HelpRequested, stateTextBox.HelpRequested, zipTextBox.HelpRequested
        ' This event is raised when the F1 key is pressed or the
        ' Help cursor is clicked on any of the address fields.
        ' The Help text for the field is in the control's
        ' Tag property. It is retrieved and displayed in the label.

        Dim requestingControl As Control = CType(sender, Control)
        helpLabel.Text = CStr(requestingControl.Tag)
        hlpevent.Handled = True

    End Sub 'textBox_HelpRequested
End Class 'Form1

[C#] 
using System;
using System.Drawing;
using System.Windows.Forms;

public class Form1 : System.Windows.Forms.Form
{
    private System.Windows.Forms.TextBox addressTextBox;
    private System.Windows.Forms.Label label2;
    private System.Windows.Forms.TextBox cityTextBox;
    private System.Windows.Forms.Label label3;
    private System.Windows.Forms.TextBox stateTextBox;
    private System.Windows.Forms.TextBox zipTextBox;
    private System.Windows.Forms.Label helpLabel;

    [STAThread]
    static void Main() 
    {
        Application.Run(new Form1());
    }

    public Form1()
    {
        this.addressTextBox = new System.Windows.Forms.TextBox();
        this.helpLabel = new System.Windows.Forms.Label();
        this.label2 = new System.Windows.Forms.Label();
        this.cityTextBox = new System.Windows.Forms.TextBox();
        this.label3 = new System.Windows.Forms.Label();
        this.stateTextBox = new System.Windows.Forms.TextBox();
        this.zipTextBox = new System.Windows.Forms.TextBox();

        // Help Label
        this.helpLabel.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D;
        this.helpLabel.Location = new System.Drawing.Point(8, 80);
        this.helpLabel.Size = new System.Drawing.Size(272, 72);
        this.helpLabel.Text = "Click on any control to give it focus, and then " +
            "press F1 to display help for that control.  Alternately, you can " +
            "click the help button at the top of the dialog and then click on a control.";

        // Address Label
        this.label2.Location = new System.Drawing.Point(16, 8);
        this.label2.Size = new System.Drawing.Size(100, 16);
        this.label2.Text = "Address:";

        // Comma Label
        this.label3.Location = new System.Drawing.Point(136, 56);
        this.label3.Size = new System.Drawing.Size(16, 16);
        this.label3.Text = ",";

        // Address TextBox
        this.addressTextBox.Location = new System.Drawing.Point(16, 24);
        this.addressTextBox.Size = new System.Drawing.Size(264, 20);
        this.addressTextBox.TabIndex = 0;
        this.addressTextBox.Tag = "Enter the street address in this text box.";
        this.addressTextBox.Text = "";
        this.addressTextBox.HelpRequested += new System.Windows.Forms.HelpEventHandler(this.textBox_HelpRequested);

        // City TextBox
        this.cityTextBox.Location = new System.Drawing.Point(16, 48);
        this.cityTextBox.Size = new System.Drawing.Size(120, 20);
        this.cityTextBox.TabIndex = 3;
        this.cityTextBox.Tag = "Enter the city here.";
        this.cityTextBox.Text = "";
        this.cityTextBox.HelpRequested += new System.Windows.Forms.HelpEventHandler(this.textBox_HelpRequested);

        // State TextBox
        this.stateTextBox.Location = new System.Drawing.Point(152, 48);
        this.stateTextBox.MaxLength = 2;
        this.stateTextBox.Size = new System.Drawing.Size(32, 20);
        this.stateTextBox.TabIndex = 5;
        this.stateTextBox.Tag = "Enter the state in this text box.";
        this.stateTextBox.Text = "";
        this.stateTextBox.HelpRequested += new System.Windows.Forms.HelpEventHandler(this.textBox_HelpRequested);

        // Zip TextBox
        this.zipTextBox.Location = new System.Drawing.Point(192, 48);
        this.zipTextBox.Name = "zipTextBox";
        this.zipTextBox.Size = new System.Drawing.Size(88, 20);
        this.zipTextBox.TabIndex = 6;
        this.zipTextBox.Tag = "Enter the zip code here.";
        this.zipTextBox.Text = "";
        this.zipTextBox.HelpRequested += new System.Windows.Forms.HelpEventHandler(this.textBox_HelpRequested);

        // Set up how the form should be displayed and add the controls to the form.
        this.ClientSize = new System.Drawing.Size(292, 160);
        this.Controls.AddRange(new System.Windows.Forms.Control[] { this.zipTextBox, 
                                this.stateTextBox, this.label3, this.cityTextBox,  
                                this.label2, this.helpLabel, this.addressTextBox});

        this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.FixedDialog;
        this.HelpButton = true;
        this.MaximizeBox = false;
        this.MinimizeBox = false;
        this.Text = "Help Event Demonstration";    
    }

    private void textBox_HelpRequested(object sender, System.Windows.Forms.HelpEventArgs hlpevent)
    {
        // This event is raised when the F1 key is pressed or the
        // Help cursor is clicked on any of the address fields.
        // The Help text for the field is in the control's
        // Tag property. It is retrieved and displayed in the label.

        Control requestingControl = (Control)sender;
        helpLabel.Text = (string)requestingControl.Tag;
        hlpevent.Handled = true;
    }
}

[C++] 
#using <mscorlib.dll>
#using <System.dll>
#using <System.Windows.Forms.dll>
#using <System.Drawing.dll>

using namespace System;
using namespace System::Drawing;
using namespace System::Windows::Forms;

public __gc class Form1 : public System::Windows::Forms::Form {
private:
   System::Windows::Forms::TextBox*  addressTextBox;
   System::Windows::Forms::Label*  label2;
   System::Windows::Forms::TextBox*  cityTextBox;
   System::Windows::Forms::Label*  label3;
   System::Windows::Forms::TextBox*  stateTextBox;
   System::Windows::Forms::TextBox*  zipTextBox;
   System::Windows::Forms::Label*  helpLabel;
public:
   Form1() {
      this->addressTextBox = new System::Windows::Forms::TextBox();
      this->helpLabel = new System::Windows::Forms::Label();
      this->label2 = new System::Windows::Forms::Label();
      this->cityTextBox = new System::Windows::Forms::TextBox();
      this->label3 = new System::Windows::Forms::Label();
      this->stateTextBox = new System::Windows::Forms::TextBox();
      this->zipTextBox = new System::Windows::Forms::TextBox();

      // Help Label
      this->helpLabel->BorderStyle = System::Windows::Forms::BorderStyle::Fixed3D;
      this->helpLabel->Location =  System::Drawing::Point(8, 80);
      this->helpLabel->Size =  System::Drawing::Size(272, 72);
      this->helpLabel->Text = S"Click on any control to give it focus, and then press F1 to display help for that control.  Alternately, you can click the help button at the top of the dialog and then click on a control.";

      // Address Label
      this->label2->Location =  System::Drawing::Point(16, 8);
      this->label2->Size =  System::Drawing::Size(100, 16);
      this->label2->Text = S"Address:";

      // Comma Label
      this->label3->Location =  System::Drawing::Point(136, 56);
      this->label3->Size =  System::Drawing::Size(16, 16);
      this->label3->Text = S", ";

      // Address TextBox
      this->addressTextBox->Location =  System::Drawing::Point(16, 24);
      this->addressTextBox->Size =  System::Drawing::Size(264, 20);
      this->addressTextBox->TabIndex = 0;
      this->addressTextBox->Tag = S"Enter the street address in this text box.";
      this->addressTextBox->Text = S"";
      this->addressTextBox->HelpRequested += new System::Windows::Forms::HelpEventHandler(this, &Form1::textBox_HelpRequested);

      // City TextBox
      this->cityTextBox->Location =  System::Drawing::Point(16, 48);
      this->cityTextBox->Size =  System::Drawing::Size(120, 20);
      this->cityTextBox->TabIndex = 3;
      this->cityTextBox->Tag = S"Enter the city here.";
      this->cityTextBox->Text = S"";
      this->cityTextBox->HelpRequested += new System::Windows::Forms::HelpEventHandler(this, &Form1::textBox_HelpRequested);

      // State TextBox
      this->stateTextBox->Location =  System::Drawing::Point(152, 48);
      this->stateTextBox->MaxLength = 2;
      this->stateTextBox->Size =  System::Drawing::Size(32, 20);
      this->stateTextBox->TabIndex = 5;
      this->stateTextBox->Tag = S"Enter the state in this text box.";
      this->stateTextBox->Text = S"";
      this->stateTextBox->HelpRequested += new System::Windows::Forms::HelpEventHandler(this, &Form1::textBox_HelpRequested);

      // Zip TextBox
      this->zipTextBox->Location =  System::Drawing::Point(192, 48);
      this->zipTextBox->Name = S"zipTextBox";
      this->zipTextBox->Size =  System::Drawing::Size(88, 20);
      this->zipTextBox->TabIndex = 6;
      this->zipTextBox->Tag = S"Enter the zip code here.";
      this->zipTextBox->Text = S"";
      this->zipTextBox->HelpRequested += new System::Windows::Forms::HelpEventHandler(this, &Form1::textBox_HelpRequested);

      // Set up how the form should be displayed and add the controls to the form.
      this->ClientSize =  System::Drawing::Size(292, 160);

      System::Windows::Forms::Control* temp0 [] = {this->zipTextBox,
         this->stateTextBox, this->label3, this->cityTextBox,
         this->label2, this->helpLabel, this->addressTextBox};

      this->Controls->AddRange(temp0);

      this->FormBorderStyle = System::Windows::Forms::FormBorderStyle::FixedDialog;
      this->HelpButton = true;
      this->MaximizeBox = false;
      this->MinimizeBox = false;
      this->Text = S"Help Event Demonstration";
   }

private:
   void textBox_HelpRequested(Object* sender, System::Windows::Forms::HelpEventArgs* hlpevent) {
      // This event is raised when the F1 key is pressed or the
      // Help cursor is clicked on any of the address fields.
      // The Help text for the field is in the control's
      // Tag property. It is retrieved and displayed in the label.

      Control* requestingControl = dynamic_cast<Control*>(sender);
      helpLabel->Text = dynamic_cast<String*>(requestingControl->Tag);
      hlpevent->Handled = true;
   }
};

[STAThread]
int main() {
   Application::Run(new Form1());
}

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Namespace: System.Windows.Forms

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family

Assembly: System.Windows.Forms (in System.Windows.Forms.dll)

See Also

System.Windows.Forms Namespace | HelpRequested | HelpEventArgs

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