Control::AllowDrop Property
Gets or sets a value indicating whether the control can accept data that the user drags onto it.
Assembly: System.Windows.Forms (in System.Windows.Forms.dll)
Property Value
Type: System::Booleantrue if drag-and-drop operations are allowed in the control; otherwise, false. The default is false.
When overriding the AllowDrop property in a derived class, use the base class's AllowDrop property to extend the base implementation. Otherwise, you must provide all the implementation. You are not required to override both the get and set accessors of the AllowDrop property; you can override only one if needed.
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: 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; } }
- UIPermission
for unrestricted Clipboard access to set this property to true. Associated enumeration: the AllClipboard value of System.Security.Permissions::UIPermissionClipboard
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.