Control.OnLocationChanged Method (System.Windows.Forms)

OnLocationChanged Method

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This page is specific to

Microsoft Visual Studio 2010/.NET Framework 4

Other versions are also available for the following:

.NET Framework Class Library

Control..::.OnLocationChanged Method

Raises the LocationChanged event.

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

Syntax

Visual Basic

Protected Overridable Sub OnLocationChanged ( _
    e As EventArgs _
)

protected virtual void OnLocationChanged(
    EventArgs e
)

Visual C++

protected:
virtual void OnLocationChanged(
    EventArgs^ e
)

abstract OnLocationChanged : 
        e:EventArgs -> unit 
override OnLocationChanged : 
        e:EventArgs -> unit

Parameters

e: Type: System..::.EventArgs
An EventArgs that contains the event data.

Remarks

Raising an event invokes the event handler through a delegate. For more information, see Raising an Event.

The OnLocationChanged method also allows 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 OnLocationChanged in a derived class, be sure to call the base class's OnLocationChanged method so that registered delegates receive the event.

Examples

The following code example is an event-raising method that is executed when the Text property value changes. The Control class has several methods with the name pattern On PropertyName Changed that raise the corresponding PropertyName Changed event when the PropertyName value changes (PropertyName represents the name of the corresponding property).

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.

Visual Basic

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);
}

Visual C++

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 );
   }

Version Information

.NET Framework

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

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Platforms

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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

Reference

Control Class

System.Windows.Forms Namespace

LocationChanged

Location