Namespace:
System.Windows.Forms
Assembly:
System.Windows.Forms (in System.Windows.Forms.dll)
Visual Basic (Declaration)
Protected Overridable Sub OnTextChanged ( _
e As EventArgs _
)
Dim e As EventArgs
Me.OnTextChanged(e)
protected virtual void OnTextChanged(
EventArgs e
)
protected:
virtual void OnTextChanged(
EventArgs^ e
)
protected function OnTextChanged(
e : EventArgs
)
Raising an event invokes the event handler through a delegate. For more information, see Raising an Event.
The OnTextChanged method also enables derived classes to handle the event without attaching a delegate. This is the preferred technique for handling the event in a derived class.
Notes to Inheritors: When overriding OnTextChanged in a derived class, be sure to call the base class's OnTextChanged method so that registered delegates receive the event.
The following code example changes the ForeColor of a TextBox derived class displaying currency data. The example converts the text to a decimal number and changes the ForeColor to Color..::.Red if the number is negative and to Color..::.Black if the number is positive. This example requires that you have a class that derives from the TextBox class.
Protected Overrides Sub OnTextChanged(e As System.EventArgs)
Try
' Convert the text to a Double and determine
' if it is a negative number.
If Double.Parse(Me.Text) < 0 Then
' If the number is negative, display it in Red.
Me.ForeColor = Color.Red
Else
' If the number is not negative, display it in Black.
Me.ForeColor = Color.Black
End If
Catch
' If there is an error, display the
' text using the system colors.
Me.ForeColor = SystemColors.ControlText
End Try
MyBase.OnTextChanged(e)
End Sub
protected override void OnTextChanged(System.EventArgs e)
{
try
{
// Convert the text to a Double and determine
// if it is a negative number.
if(double.Parse(this.Text) < 0)
{
// If the number is negative, display it in Red.
this.ForeColor = Color.Red;
}
else
{
// If the number is not negative, display it in Black.
this.ForeColor = Color.Black;
}
}
catch
{
// If there is an error, display the
// text using the system colors.
this.ForeColor = SystemColors.ControlText;
}
base.OnTextChanged(e);
}
protected:
virtual void OnTextChanged( System::EventArgs^ e ) override
{
try
{
// Convert the text to a Double and determine
// if it is a negative number.
if ( Double::Parse( this->Text ) < 0 )
{
// If the number is negative, display it in Red.
this->ForeColor = Color::Red;
}
else
{
// If the number is not negative, display it in Black.
this->ForeColor = Color::Black;
}
}
catch ( Exception^ )
{
// If there is an error, display the
// text using the system colors.
this->ForeColor = SystemColors::ControlText;
}
TextBox::OnTextChanged( e );
}
Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC
The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
.NET Framework
Supported in: 3.5, 3.0, 2.0, 1.1, 1.0
.NET Compact Framework
Supported in: 3.5, 2.0, 1.0
Reference