Control.OnTextChanged(EventArgs) Method

Reference

Definition

Namespace:: System.Windows.Forms

Assembly:: System.Windows.Forms.dll

Important

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Raises the TextChanged event.

protected:
 virtual void OnTextChanged(EventArgs ^ e);

protected virtual void OnTextChanged (EventArgs e);

abstract member OnTextChanged : EventArgs -> unit
override this.OnTextChanged : EventArgs -> unit

Protected Overridable Sub OnTextChanged (e As EventArgs)

Parameters

e: EventArgs

An EventArgs that contains the event data.

Examples

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:
   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 );
   }

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 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

Remarks

Raising an event invokes the event handler through a delegate. For more information, see Handling and Raising Events.

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(EventArgs) in a derived class, be sure to call the base class's OnTextChanged(EventArgs) method so that registered delegates receive the event.

Applies to

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