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HelpEventHandler Delegate

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

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

public delegate void HelpEventHandler(
	Object^ sender, 
	HelpEventArgs^ hlpevent
)

Parameters

sender
Type: System::Object

The source of the event.

hlpevent
Type: System.Windows.Forms::HelpEventArgs

A HelpEventArgs that contains the event data.

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 Handling and Raising Events.

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.

#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 ref 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 = gcnew System::Windows::Forms::TextBox;
      this->helpLabel = gcnew System::Windows::Forms::Label;
      this->label2 = gcnew System::Windows::Forms::Label;
      this->cityTextBox = gcnew System::Windows::Forms::TextBox;
      this->label3 = gcnew System::Windows::Forms::Label;
      this->stateTextBox = gcnew System::Windows::Forms::TextBox;
      this->zipTextBox = gcnew 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 = "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 = "Address:";

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

      // 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 = "Enter the street address in this text box.";
      this->addressTextBox->Text = "";
      this->addressTextBox->HelpRequested += gcnew 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 = "Enter the city here.";
      this->cityTextBox->Text = "";
      this->cityTextBox->HelpRequested += gcnew 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 = "Enter the state in this text box.";
      this->stateTextBox->Text = "";
      this->stateTextBox->HelpRequested += gcnew System::Windows::Forms::HelpEventHandler( this, &Form1::textBox_HelpRequested );

      // Zip TextBox 
      this->zipTextBox->Location = System::Drawing::Point( 192, 48 );
      this->zipTextBox->Name = "zipTextBox";
      this->zipTextBox->Size = System::Drawing::Size( 88, 20 );
      this->zipTextBox->TabIndex = 6;
      this->zipTextBox->Tag = "Enter the zip code here.";
      this->zipTextBox->Text = "";
      this->zipTextBox->HelpRequested += gcnew 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 );
      array<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 = "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( gcnew Form1 );
}

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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