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Control.OnPaint Method

Raises the Paint event.

[Visual Basic]
Protected Overridable Sub OnPaint( _
   ByVal e As PaintEventArgs _
)
[C#]
protected virtual void OnPaint(
 PaintEventArgs e
);
[C++]
protected: virtual void OnPaint(
 PaintEventArgs* e
);
[JScript]
protected function OnPaint(
   e : PaintEventArgs
);

Parameters

e
A PaintEventArgs that contains the event data.

Remarks

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

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

Example

[Visual Basic, C#, C++] The following example enables the user to drag an image or image file onto the form, and have it be displayed at the point on it is dropped. The OnPaint method is overridden to repaint the image each time the form is painted; otherwise the image would only persist until the next repainting. The DragEnter event-handling method determines the type of data being dragged into the form and provides the appropriate feedback. The DragDrop event-handling method displays the image on the form, if an Image can be created from the data. Because the DragEventArgs.X and DragEventArgs.Y values are screen coordinates, the example uses the PointToClient method to convert them to client coordinates.

[Visual Basic] 
Private picture As Image
Private pictureLocation As Point

Public Sub New()
   ' Enable drag-and-drop operations.
   Me.AllowDrop = True
End Sub

Protected Overrides Sub OnPaint(ByVal e As PaintEventArgs)
   MyBase.OnPaint(e)

   ' If there is an image and it has a location, 
   ' paint it when the Form is repainted.
   If Not (Me.picture Is Nothing) And _
     Not (Me.pictureLocation.Equals(Point.Empty)) Then
      e.Graphics.DrawImage(Me.picture, Me.pictureLocation)
   End If
End Sub

Private Sub Form1_DragDrop(ByVal sender As Object, _
  ByVal e As DragEventArgs) Handles MyBase.DragDrop
   ' Handle FileDrop data.
   If e.Data.GetDataPresent(DataFormats.FileDrop) Then
      ' Assign the file names to a string array, in 
      ' case the user has selected multiple files.
      Dim files As String() = CType(e.Data.GetData(DataFormats.FileDrop), String())
      Try
         ' Assign the first image to the 'picture' variable.
         Me.picture = Image.FromFile(files(0))
         ' Set the picture location equal to the drop point.
         Me.pictureLocation = Me.PointToClient(New Point(e.X, e.Y))
      Catch ex As Exception
         MessageBox.Show(ex.Message)
         Return
      End Try
   End If

   ' Handle Bitmap data.
   If e.Data.GetDataPresent(DataFormats.Bitmap) Then
      Try
         ' Create an Image and assign it to the picture variable.
         Me.picture = CType(e.Data.GetData(DataFormats.Bitmap), Image)
         ' Set the picture location equal to the drop point.
         Me.pictureLocation = Me.PointToClient(New Point(e.X, e.Y))
      Catch ex As Exception
         MessageBox.Show(ex.Message)
         Return
      End Try
   End If

   ' Force the form to be redrawn with the image.
   Me.Invalidate()
End Sub

Private Sub Form1_DragEnter(ByVal sender As Object, _
  ByVal e As DragEventArgs) Handles MyBase.DragEnter
   ' If the data is a file or a bitmap, display the copy cursor.
   If e.Data.GetDataPresent(DataFormats.Bitmap) _
      Or e.Data.GetDataPresent(DataFormats.FileDrop) Then
      e.Effect = DragDropEffects.Copy
   Else
      e.Effect = DragDropEffects.None
   End If
End Sub

[C#] 
private Image picture;
private Point pictureLocation;

public Form1()
{
   // Enable drag-and-drop operations and 
   // add handlers for DragEnter and DragDrop.
   this.AllowDrop = true;
   this.DragDrop += new DragEventHandler(this.Form1_DragDrop);
   this.DragEnter += new DragEventHandler(this.Form1_DragEnter);
}

protected override void OnPaint(PaintEventArgs e)
{
   // If there is an image and it has a location, 
   // paint it when the Form is repainted.
   base.OnPaint(e);
   if(this.picture != null && this.pictureLocation != Point.Empty)
   {
      e.Graphics.DrawImage(this.picture, this.pictureLocation);
   }
}

private void Form1_DragDrop(object sender, DragEventArgs e)
{
   // Handle FileDrop data.
   if(e.Data.GetDataPresent(DataFormats.FileDrop) )
   {
      // Assign the file names to a string array, in 
      // case the user has selected multiple files.
      string[] files = (string[])e.Data.GetData(DataFormats.FileDrop);
      try
      {
         // Assign the first image to the picture variable.
         this.picture = Image.FromFile(files[0]);
         // Set the picture location equal to the drop point.
         this.pictureLocation = this.PointToClient(new Point(e.X, e.Y) );
      }
      catch(Exception ex)
      {
         MessageBox.Show(ex.Message);
         return;
      }
   }

   // Handle Bitmap data.
   if(e.Data.GetDataPresent(DataFormats.Bitmap) )
   {
      try
      {
         // Create an Image and assign it to the picture variable.
         this.picture = (Image)e.Data.GetData(DataFormats.Bitmap);
         // Set the picture location equal to the drop point.
         this.pictureLocation = this.PointToClient(new Point(e.X, e.Y) );
      }
      catch(Exception ex)
      {
         MessageBox.Show(ex.Message);
         return;
      }
   }
   // Force the form to be redrawn with the image.
   this.Invalidate();
}

private void Form1_DragEnter(object sender, DragEventArgs e)
{
   // If the data is a file or a bitmap, display the copy cursor.
   if (e.Data.GetDataPresent(DataFormats.Bitmap) || 
      e.Data.GetDataPresent(DataFormats.FileDrop) ) 
   {
      e.Effect = DragDropEffects.Copy;
   }
   else
   {
      e.Effect = DragDropEffects.None;
   }
}

[C++] 
private:
   Image*  picture;
   Point  pictureLocation;

public:
   Form1() {
      // Enable drag-and-drop operations and
      // add handlers for DragEnter and DragDrop.
      this->AllowDrop = true;
      this->DragDrop += new DragEventHandler(this, &Form1::Form1_DragDrop);
      this->DragEnter += new DragEventHandler(this, &Form1::Form1_DragEnter);
   }

protected:
   void OnPaint(PaintEventArgs* e) {
      // If there is an image and it has a location,
      // paint it when the Form is repainted.
      Form::OnPaint(e);
      if (this->picture != 0 && this->pictureLocation != Point::Empty) {
         e->Graphics->DrawImage(this->picture, this->pictureLocation);
      }
   }

private:
   void Form1_DragDrop(Object* /*sender*/, DragEventArgs* e) {
      // Handle FileDrop data.
      if (e->Data->GetDataPresent(DataFormats::FileDrop)) {
         // Assign the file names to a String* array, in
         // case the user has selected multiple files.
         String* files[] = (String*[])e->Data->GetData(DataFormats::FileDrop);
         try {
            // Assign the first image to the picture variable.
            this->picture = Image::FromFile(files[0]);
            // Set the picture location equal to the drop point.
            this->pictureLocation = this->PointToClient( Point(e->X, e->Y));
         } catch (Exception* ex) {
            MessageBox::Show(ex->Message);
            return;
         }
      }

      // Handle Bitmap data.
      if (e->Data->GetDataPresent(DataFormats::Bitmap)) {
         try {
            // Create an Image and assign it to the picture variable.
            this->picture = dynamic_cast<Image*>(e->Data->GetData(DataFormats::Bitmap));
            // Set the picture location equal to the drop point.
            this->pictureLocation = this->PointToClient( Point(e->X, e->Y));
         } catch (Exception* ex) {
            MessageBox::Show(ex->Message);
            return;
         }
      }
      // Force the form to be redrawn with the image.
      this->Invalidate();
   }

   void Form1_DragEnter(Object* /*sender*/, DragEventArgs* e) {
      // If the data is a file or a bitmap, display the copy cursor.
      if (e->Data->GetDataPresent(DataFormats::Bitmap) ||
         e->Data->GetDataPresent(DataFormats::FileDrop)) {
            e->Effect = DragDropEffects::Copy;
         } else {
            e->Effect = DragDropEffects::None;
         }
   }

[Visual Basic] 
' This example creates a PictureBox control on the form and draws to it. 
' This example assumes that the Form_Load event handling method is connected 
' to the Load event of the form.
Private pictureBox1 As New PictureBox()

Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Load
    ' Dock the PictureBox to the form and set its background to white.
    pictureBox1.Dock = DockStyle.Fill
    pictureBox1.BackColor = Color.White
    ' Connect the Paint event of the PictureBox to the event handling method.
    AddHandler pictureBox1.Paint, AddressOf Me.pictureBox1_Paint

    ' Add the PictureBox control to the Form.
    Me.Controls.Add(pictureBox1)
End Sub 'Form1_Load


Private Sub pictureBox1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs)
    ' Create a local version of the graphics object for the PictureBox.
    Dim g As Graphics = e.Graphics

    ' Draw a string on the PictureBox.
    g.DrawString("This is a diagonal line drawn on the control", _
        New Font("Arial", 10), Brushes.Red, New PointF(30.0F, 30.0F))
    ' Draw a line in the PictureBox.
    g.DrawLine(System.Drawing.Pens.Red, pictureBox1.Left, _ 
        pictureBox1.Top, pictureBox1.Right, pictureBox1.Bottom)
End Sub 'pictureBox1_Paint

[C#] 
// This example creates a PictureBox control on the form and draws to it.
// This example assumes that the Form_Load event handling method is
// connected to the Load event of the form.

private PictureBox pictureBox1 = new PictureBox();
private void Form1_Load(object sender, System.EventArgs e)
{
    // Dock the PictureBox to the form and set its background to white.
    pictureBox1.Dock = DockStyle.Fill;
    pictureBox1.BackColor = Color.White;
    // Connect the Paint event of the PictureBox to the event handling method.
    pictureBox1.Paint += new System.Windows.Forms.PaintEventHandler(this.pictureBox1_Paint);

    // Add the PictureBox control to the Form.
    this.Controls.Add(pictureBox1);
}

private void pictureBox1_Paint(object sender, System.Windows.Forms.PaintEventArgs e)
{
    // Create a local version of the graphics object for the PictureBox.
    Graphics g = e.Graphics;

    // Draw a string on the PictureBox.
    g.DrawString("This is a diagonal line drawn on the control",
        new Font("Arial",10), System.Drawing.Brushes.Blue, new Point(30,30));
    // Draw a line in the PictureBox.
    g.DrawLine(System.Drawing.Pens.Red, pictureBox1.Left, pictureBox1.Top,
        pictureBox1.Right, pictureBox1.Bottom);
}

[C++] 
// This example creates a PictureBox control on the form and draws to it.
// This example assumes that the Form_Load event handling method is
// connected to the Load event of the form.

private:
PictureBox* pictureBox1;

void Form1_Load(Object* /*sender*/, System::EventArgs* /*e*/)
{
   pictureBox1 = new PictureBox();
   // Dock the PictureBox to the form and set its background to white.
   pictureBox1->Dock = DockStyle::Fill;
   pictureBox1->BackColor = Color::White;
   // Connect the Paint event of the PictureBox to the event handling method.
   pictureBox1->Paint += new System::Windows::Forms::PaintEventHandler(this, &Form1::pictureBox1_Paint);

   // Add the PictureBox control to the Form.
   this->Controls->Add(pictureBox1);
}

void pictureBox1_Paint(Object* /*sender*/, System::Windows::Forms::PaintEventArgs* e)
{
   // Create a local version of the graphics object for the PictureBox.
   Graphics* g = e->Graphics;

   // Draw a string on the PictureBox.
   g->DrawString(S"This is a diagonal line drawn on the control",
      new System::Drawing::Font(S"Arial",10), System::Drawing::Brushes::Blue, Point(30,30));
   // Draw a line in the PictureBox.
   g->DrawLine(System::Drawing::Pens::Red, pictureBox1->Left, pictureBox1->Top,
      pictureBox1->Right, pictureBox1->Bottom);
}

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family, .NET Compact Framework

See Also

Control Class | Control Members | System.Windows.Forms Namespace | Paint

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