KeyEventArgs Class
Definition
Important
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public ref class KeyEventArgs : EventArgs[System.Runtime.InteropServices.ComVisible(true)]
public class KeyEventArgs : EventArgspublic class KeyEventArgs : EventArgs[<System.Runtime.InteropServices.ComVisible(true)>]
type KeyEventArgs = class
inherit EventArgstype KeyEventArgs = class
inherit EventArgsPublic Class KeyEventArgs
Inherits EventArgs- Inheritance
- Attributes
Examples
The following code examples demonstrate how to detect the state of a key press.
Example 1
The following code example demonstrates how to use the KeyDown event with the Help class to display pop-up style Help to the user of the application. The example uses the KeyEventArgs properties passed to the event handler method to filter for all variations of pressing the F1 key with a modifier key. When the user presses any variation of F1 that includes any keyboard modifier, the Help class displays a pop-up window, similar to a ToolTip, near the control. If the user presses ALT+F2, a different Help pop-up is displayed with additional information.
// This example demonstrates how to use the KeyDown event with the Help class to display
// pop-up style help to the user of the application. The example filters for all variations
// of pressing the F1 key with a modifier key by using the KeyEventArgs properties passed
// to the event handling method.
// When the user presses any variation of F1 that includes any keyboard modifier, the Help
// class displays a pop-up window, similar to a ToolTip, near the control. If the user presses
// ALT + F2, a different Help pop-up is displayed with additional information. This example assumes
// that a tTextBox control, named textBox1, has been added to the form and its KeyDown
// event has been contected to this event handling method.
private:
void textBox1_KeyDown( Object^ /*sender*/, System::Windows::Forms::KeyEventArgs^ e )
{
// Determine whether the key entered is the F1 key. If it is, display Help.
if ( e->KeyCode == Keys::F1 && (e->Alt || e->Control || e->Shift) )
{
// Display a pop-up Help topic to assist the user.
Help::ShowPopup( textBox1, "Enter your name.", Point(textBox1->Bottom,textBox1->Right) );
}
else
if ( e->KeyCode == Keys::F2 && e->Modifiers == Keys::Alt )
{
// Display a pop-up Help topic to provide additional assistance to the user.
Help::ShowPopup( textBox1, "Enter your first name followed by your last name. Middle name is optional.",
Point(textBox1->Top,this->textBox1->Left) );
}
}
private void textBox1_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
{
// Determine whether the key entered is the F1 key. If it is, display Help.
if(e.KeyCode == Keys.F1 && (e.Alt || e.Control || e.Shift))
{
// Display a pop-up Help topic to assist the user.
Help.ShowPopup(textBox1, "Enter your name.", new Point(textBox1.Bottom, textBox1.Right));
}
else if(e.KeyCode == Keys.F2 && e.Modifiers == Keys.Alt)
{
// Display a pop-up Help topic to provide additional assistance to the user.
Help.ShowPopup(textBox1, "Enter your first name followed by your last name. Middle name is optional.",
new Point(textBox1.Top, this.textBox1.Left));
}
}
Private Sub textBox1_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles textBox1.KeyDown
' Determine whether the key entered is the F1 key. If it is, display Help.
If e.KeyCode = Keys.F1 AndAlso (e.Alt OrElse e.Control OrElse e.Shift) Then
' Display a pop-up Help topic to assist the user.
Help.ShowPopup(textBox1, "Enter your name.", New Point(textBox1.Bottom, textBox1.Right))
ElseIf e.KeyCode = Keys.F2 AndAlso e.Modifiers = Keys.Alt Then
' Display a pop-up Help topic to provide additional assistance to the user.
Help.ShowPopup(textBox1, "Enter your first name followed by your last name. Middle name is optional.", _
New Point(textBox1.Top, Me.textBox1.Left))
End If
End Sub
Example 2
The following example determines whether the user pressed ALT+E, and if the mouse pointer is over a TreeNode, allows the user to edit that TreeNode.
private:
void treeView1_KeyDown( Object^ /*sender*/, KeyEventArgs^ e )
{
/* If the 'Alt' and 'E' keys are pressed,
* allow the user to edit the TreeNode label. */
if ( e->Alt && e->KeyCode == Keys::E )
{
treeView1->LabelEdit = true;
// If there is a TreeNode under the mouse cursor, begin editing.
TreeNode^ editNode = treeView1->GetNodeAt( treeView1->PointToClient( Control::MousePosition ) );
if ( editNode != nullptr )
{
editNode->BeginEdit();
}
}
}
void treeView1_AfterLabelEdit( Object^ /*sender*/, NodeLabelEditEventArgs^ /*e*/ )
{
// Disable the ability to edit the TreeNode labels.
treeView1->LabelEdit = false;
}
private void treeView1_KeyDown(object sender, KeyEventArgs e)
{
/* If the 'Alt' and 'E' keys are pressed,
* allow the user to edit the TreeNode label. */
if(e.Alt && e.KeyCode == Keys.E)
{
treeView1.LabelEdit = true;
// If there is a TreeNode under the mouse cursor, begin editing.
TreeNode editNode = treeView1.GetNodeAt(
treeView1.PointToClient(System.Windows.Forms.Control.MousePosition));
if(editNode != null)
{
editNode.BeginEdit();
}
}
}
private void treeView1_AfterLabelEdit(object sender, NodeLabelEditEventArgs e)
{
// Disable the ability to edit the TreeNode labels.
treeView1.LabelEdit = false;
}
Private Sub treeView1_KeyDown(sender As Object, _
e As KeyEventArgs) Handles treeView1.KeyDown
' If the 'Alt' and 'E' keys are pressed,
' allow the user to edit the TreeNode label.
If e.Alt And e.KeyCode = Keys.E Then
treeView1.LabelEdit = True
' If there is a TreeNode under the mouse cursor, begin editing.
Dim editNode As TreeNode = treeView1.GetNodeAt( _
treeView1.PointToClient(System.Windows.Forms.Control.MousePosition))
If (editNode IsNot Nothing) Then
editNode.BeginEdit()
End If
End If
End Sub
Private Sub treeView1_AfterLabelEdit(sender As Object, _
e As NodeLabelEditEventArgs) Handles treeView1.AfterLabelEdit
' Disable the ability to edit the TreeNode labels.
treeView1.LabelEdit = False
End Sub
Example 3
The following example determines whether the user pressed a non-numeric key, and if so, cancels the KeyPress event by using the Handled property.
// Boolean flag used to determine when a character other than a number is entered.
private:
bool nonNumberEntered;
// Handle the KeyDown event to determine the type of character entered into the control.
void textBox1_KeyDown( Object^ /*sender*/, System::Windows::Forms::KeyEventArgs^ e )
{
// Initialize the flag to false.
nonNumberEntered = false;
// Determine whether the keystroke is a number from the top of the keyboard.
if ( e->KeyCode < Keys::D0 || e->KeyCode > Keys::D9 )
{
// Determine whether the keystroke is a number from the keypad.
if ( e->KeyCode < Keys::NumPad0 || e->KeyCode > Keys::NumPad9 )
{
// Determine whether the keystroke is a backspace.
if ( e->KeyCode != Keys::Back )
{
// A non-numerical keystroke was pressed.
// Set the flag to true and evaluate in KeyPress event.
nonNumberEntered = true;
}
}
}
//If shift key was pressed, it's not a number.
if (Control::ModifierKeys == Keys::Shift) {
nonNumberEntered = true;
}
}
// This event occurs after the KeyDown event and can be used to prevent
// characters from entering the control.
void textBox1_KeyPress( Object^ /*sender*/, System::Windows::Forms::KeyPressEventArgs^ e )
{
// Check for the flag being set in the KeyDown event.
if ( nonNumberEntered == true )
{ // Stop the character from being entered into the control since it is non-numerical.
e->Handled = true;
}
}
// Boolean flag used to determine when a character other than a number is entered.
private bool nonNumberEntered = false;
// Handle the KeyDown event to determine the type of character entered into the control.
private void textBox1_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
{
// Initialize the flag to false.
nonNumberEntered = false;
// Determine whether the keystroke is a number from the top of the keyboard.
if (e.KeyCode < Keys.D0 || e.KeyCode > Keys.D9)
{
// Determine whether the keystroke is a number from the keypad.
if (e.KeyCode < Keys.NumPad0 || e.KeyCode > Keys.NumPad9)
{
// Determine whether the keystroke is a backspace.
if(e.KeyCode != Keys.Back)
{
// A non-numerical keystroke was pressed.
// Set the flag to true and evaluate in KeyPress event.
nonNumberEntered = true;
}
}
}
//If shift key was pressed, it's not a number.
if (Control.ModifierKeys == Keys.Shift) {
nonNumberEntered = true;
}
}
// This event occurs after the KeyDown event and can be used to prevent
// characters from entering the control.
private void textBox1_KeyPress(object sender, System.Windows.Forms.KeyPressEventArgs e)
{
// Check for the flag being set in the KeyDown event.
if (nonNumberEntered == true)
{
// Stop the character from being entered into the control since it is non-numerical.
e.Handled = true;
}
}
' Boolean flag used to determine when a character other than a number is entered.
Private nonNumberEntered As Boolean = False
' Handle the KeyDown event to determine the type of character entered into the control.
Private Sub textBox1_KeyDown(sender As Object, e As System.Windows.Forms.KeyEventArgs) _
Handles textBox1.KeyDown
' Initialize the flag to false.
nonNumberEntered = False
' Determine whether the keystroke is a number from the top of the keyboard.
If e.KeyCode < Keys.D0 OrElse e.KeyCode > Keys.D9 Then
' Determine whether the keystroke is a number from the keypad.
If e.KeyCode < Keys.NumPad0 OrElse e.KeyCode > Keys.NumPad9 Then
' Determine whether the keystroke is a backspace.
If e.KeyCode <> Keys.Back Then
' A non-numerical keystroke was pressed.
' Set the flag to true and evaluate in KeyPress event.
nonNumberEntered = True
End If
End If
End If
'If shift key was pressed, it's not a number.
If Control.ModifierKeys = Keys.Shift Then
nonNumberEntered = true
End If
End Sub
' This event occurs after the KeyDown event and can be used
' to prevent characters from entering the control.
Private Sub textBox1_KeyPress(sender As Object, e As System.Windows.Forms.KeyPressEventArgs) _
Handles textBox1.KeyPress
' Check for the flag being set in the KeyDown event.
If nonNumberEntered = True Then
' Stop the character from being entered into the control since it is non-numerical.
e.Handled = True
End If
End Sub
Remarks
A KeyEventArgs, which specifies the key the user pressed and whether any modifier keys (CTRL, ALT, and SHIFT) were pressed at the same time, is passed with each KeyDown or KeyUp event.
The KeyDown event occurs when the user presses any key. The KeyUp event occurs when the user releases the key. Duplicate KeyDown events occur each time the key repeats, if the key is held down, but only one KeyUp event is generated when the user releases the key.
The KeyPress event also occurs when a key is pressed. A KeyPressEventArgs is passed with each KeyPress event, and specifies the character that was composed as a result of each key press.
For information about the event model, see Handling and Raising Events.
Constructors
| KeyEventArgs(Keys) |
Initializes a new instance of the KeyEventArgs class. |
Properties
| Alt |
Gets a value indicating whether the ALT key was pressed. |
| Control |
Gets a value indicating whether the CTRL key was pressed. |
| Handled |
Gets or sets a value indicating whether the event was handled. |
| KeyCode | |
| KeyData | |
| KeyValue | |
| Modifiers |
Gets the modifier flags for a KeyDown or KeyUp event. The flags indicate which combination of CTRL, SHIFT, and ALT keys was pressed. |
| Shift |
Gets a value indicating whether the SHIFT key was pressed. |
| SuppressKeyPress |
Gets or sets a value indicating whether the key event should be passed on to the underlying control. |
Methods
| Equals(Object) |
Determines whether the specified object is equal to the current object. (Inherited from Object) |
| GetHashCode() |
Serves as the default hash function. (Inherited from Object) |
| GetType() |
Gets the Type of the current instance. (Inherited from Object) |
| MemberwiseClone() |
Creates a shallow copy of the current Object. (Inherited from Object) |
| ToString() |
Returns a string that represents the current object. (Inherited from Object) |
