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()); }
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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