Invalidates the entire surface of the control and causes the control to be redrawn.
Namespace:
System.Windows.Forms
Assembly:
System.Windows.Forms (in System.Windows.Forms.dll)
Visual Basic (Declaration)
Dim instance As Control
instance.Invalidate()
public:
void Invalidate()
public function Invalidate()
Calling the Invalidate method does not force a synchronous paint; to force a synchronous paint, call the Update method after calling the Invalidate method. When this method is called with no parameters, the entire client area is added to the update region.
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 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
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:
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;
}
}
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