Control.OnPaint(PaintEventArgs) Method

Reference

Definition

Namespace:: System.Windows.Forms

Assembly:: System.Windows.Forms.dll

Source:: Control.cs

Source:: Control.cs

Source:: Control.cs

Important

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Raises the Paint event.

protected:
 virtual void OnPaint(System::Windows::Forms::PaintEventArgs ^ e);

protected virtual void OnPaint (System.Windows.Forms.PaintEventArgs e);

abstract member OnPaint : System.Windows.Forms.PaintEventArgs -> unit
override this.OnPaint : System.Windows.Forms.PaintEventArgs -> unit

Protected Overridable Sub OnPaint (e As PaintEventArgs)

Parameters

e: PaintEventArgs

A PaintEventArgs that contains the event data.

Examples

The following code example enables the user to drag an image or image file onto the form, and have it be displayed at the point on which 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.

private:
   Image^ picture;
   Point pictureLocation;

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

protected:
   virtual void OnPaint( PaintEventArgs^ e ) override
   {
      
      // If there is an image and it has a location,
      // paint it when the Form is repainted.
      Form::OnPaint( e );
      if ( this->picture != nullptr && 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.
         array<String^>^files = (array<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;
      }
   }

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;
   }
}

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 (Me.picture IsNot 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

   // This example creates a PictureBox control on the form and draws to it.
   // This example assumes that the Form_Load event handler method is
   // connected to the Load event of the form.
private:
   PictureBox^ pictureBox1;
   void Form1_Load( Object^ /*sender*/, System::EventArgs^ /*e*/ )
   {
      pictureBox1 = gcnew 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 handler method.
      pictureBox1->Paint += gcnew 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( "This is a diagonal line drawn on the control",
         gcnew System::Drawing::Font( "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 );
   }

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

private PictureBox pictureBox1 = new PictureBox();
// Cache font instead of recreating font objects each time we paint.
private Font fnt = new Font("Arial",10);
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 handler 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",
        fnt, 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);
}

' This example creates a PictureBox control on the form and draws to it. 
' This example assumes that the Form_Load event handler method is connected 
' to the Load event of the form.
Private pictureBox1 As New PictureBox()
Private fnt as New Font("Arial", 10)

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 handler method.
    AddHandler pictureBox1.Paint, AddressOf Me.pictureBox1_Paint

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


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", _
        fnt, 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

Remarks

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

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

Applies to

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