Namespace:
System.Windows.Forms
Assembly:
System.Windows.Forms (in System.Windows.Forms.dll)
'Usage
Dim e As PaintEventArgs
Me.OnPaint(e)
'Declaration
Protected Overridable Sub OnPaint ( _
e As PaintEventArgs _
)
Raising an event invokes the event handler through a delegate. For more information, see Raising an Event.
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 in a derived class, be sure to call the base class's OnPaint method so that registered delegates receive the event.
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 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 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 handler 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
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