3. Conversion of manual OLE Drag and Drop

VB6 OLE Drag and Drop is very different to VB6 Standard Drag and Drop. OLE Drag and Drop has more events and handlers to enhance the functionality, so its conversion to .NET will be very different as well.

3.1. OLEDrag method

VB6 manual OLE Drag and Drop starts with the object.OLEDrag method. However, this Drag and Drop variant requires to set the Drag data and the allowed drag methods inside the OLEStartDrag event handler. To convert the original OLE Drag and Drop behavior to .NET, the OLEDrag and OLEStartDrag members will be converted together.

3.1.1. Source code

theControl.OLEDrag

3.1.2. Expected code

The call to OLEDrag method will be replaced to the converted OLEStartDrag member. The settings for the drag and drop action will be defined inside that method.

Visual Basic .NET

'UPGRADE_WARNING: The following statement was inserted to allow conversion of drag start event
theControl_OLEStartDrag()

C#

//UPGRADE_WARNING: The following statement was inserted to allow conversion of drag start event
theControl_OLEStartDrag();

3.2. OLEStartDrag

This event was raised in the source control at the start of the drag and drop operation caused by a call to the OLEDrag method of the control. (See 3.1.)

3.2.1. Source code

Private Sub theControl_OLEStartDrag(Data As DataObject, AllowedEffects As Long)
     Data.SetData theControl.SelText, vbCFText
     AllowedEffects = vbDropEffectCopy 
End Sub

3.2.2. Expected code

Data and AllowedEffects parameters are no longer necessary in the converted method header, since the data and the allowed modes are passed in the call to the control’s DoDragDrop method.

Convert the Data.SetData and AllowedEffects assignations into one call to DoDragDrop method.

The call to DoDragDrop method returns the drag and drop effect accepted when the operation ends. It will be stored to support the conversion of other VB6 OLE drag and drop events.

Visual Basic .NET

Private Sub theControl_OLEStartDrag()
   Dim Effect As DragDropEffects
   Effect = theControl.DoDragDrop(theControl.SelectedText, DragDropEffects.Copy)
End Sub

C#

private void theControl_OLEStartDrag( )
{ 
   DragDropEffects effect;
   effect = theControl.DoDragDrop(theControl.SelectedText, DragDropEffects.Copy);
}

3.3. OLEDragOver event

The DragOver event is received by a target control when the mouse pointer passes over the control during a drag and drop operation.

.NET controls require to have the AllowDrop property set to True in the designer code section to be capable of handling of DragDrop and DragOver events.

It’s also very important to note that every control which receives DragDrop actions has to allow the drag and drop operation first. The types of allowed drag and drop operations are set with a DragDropEffect value in the drag over or drag enter event handlers. As a default for this spec, the DragDropEffect value will be set in the DragEnter event handler.

If the original code didn’t had code to handle the drag over events, the conversion process has to insert a DragEnter event handler to allow the drag and drop.

3.3.1. Source code

Private Sub theControl_OLEDragOver(Data As DataObject, Effect As Long, Button As Integer, Shift As Integer, X As Single, Y As Single, State As Integer)
    'User's code
    If Data.GetFormat(vbCFText) Then
        Effect = vbDropEffectCopy 
    Else
        Effect = vbDropEffectNone
End If
'End of user's code
End Sub

3.3.2. Expected code

First of all, add the following line of code to the designer code for the control. This allows the control to receive drag and drop events.

Visual Basic .NET

theControl.AllowDrop = True

C#

theControl.AllowDrop = true;

Remove all the original parameters but State. Insert a new DragEventArgs parameter as first parameter. Rename the event handler to control_DragOverEvent to avoid name conflicts with control’s .NET event handlers.

Note the required conversion of .NET event’s screen coordinates to client control coordinates, using the ConvertCoordinatesToClient support method.

Visual Basic .NET

Private Sub theControl_OLEDragOverEvent(ByRef e As DragEventArgs, ByRef State As Short)
   Dim x As Integer = e.X
   Dim y As Integer = e.Y
   Dim Button As Integer = e.KeyState \ &H100000
   Dim Shift As Integer = Control.ModifierKeys \ &H10000
   Support.ConvertCoordinatesToClient(theControl, x, y)
   'User's code
   If e.Data.GetDataPresent(DataFormats.Text) Then
      e.Effect = DragDropEffects.Copy
   Else
      e.Effect = DragDropEffects.None
   End If
   'End of user's code
End Sub

C#

private void  theControl_OLEDragOverEvent( DragEventArgs e,  short State)
{
   int X = e.X;
   int Y = e.Y;
   int Button = e.KeyState | 0x100000;
   int Shift = (int)Control.ModifierKeys | 0x10000;
   Support.ConvertCoordinatesToClient(Text1, ref X, ref Y);

  //User's code
   if (e.Data.GetDataPresent(DataFormats.Text))
   {
      e.Effect = DragDropEffects.Copy;
   }
  else
   {
      e.Effect = DragDropEffects.None;
   }
   //End of user's code
}

Generate the drag enter, over and leave event handlers for the Control which is receiving the drag and drop event. Insert calls to the above method in the generated event handlers, adding the expected parameters.

Also, add the line required to allow the Drag and Drop operations in the DragEnter event handler.

Visual Basic .NET

Private Sub theControl_DragEnter(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs) Handles theControl.DragEnter
   e.Effect = DragDropEffects.All
   theControl_OLEDragOverEvent(e, 0)
End Sub

Private Sub theControl_DragLeave(ByVal sender As Object, ByVal e As System.EventArgs) Handles theControl.DragLeave
   theControl_OLEDragOverEvent(New DragEventArgs(Nothing, 0, 0, 0, DragDropEffects.All, DragDropEffects.All), 1)
End Sub

Private Sub theControl_DragOver(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs) Handles theControl.DragOver
   theControl_OLEDragOverEvent(e, 2)
End Sub

C#

private void theControl_DragEnter(object sender, DragEventArgs e)
{
   e.Effect = DragDropEffects.All;
   theControl_OLEDragOverEvent(e, 0);
}

private void theControl_DragLeave(object sender, EventArgs e)
{
   theControl_OLEDragOverEvent(new DragEventArgs(null,0,0,0,DragDropEffects.All,DragDropEffects.All), 1);
}

private void theControl_DragOver(object sender, DragEventArgs e)
{
   theControl_OLEDragOverEvent(e, 2);
}

3.3.4. Required support methods

Add the following support methods to the project’s Support class. GetSourceObject method is used to extract the instance of the source control of the drag and drop process. ConvertCoordinatesToClient method is used to convert the screen coordinates produced by .NET events to coordinates inside the control which is receiving the event

Visual Basic .NET

'Convert .NET event's screen coordinates to client control coordinates to be used by converted drag and drop members
Public Sub ConvertCoordinatesToClient(ByVal clientControl As Control, ByRef x As Integer, ByRef y As Integer)
   Dim convertedCoordinates As Point = clientControl.PointToClient(New Point(x, y))
   x = convertedCoordinates.X
   y = convertedCoordinates.Y
End Sub

C#

class Support
{

   /// <summary>
   /// Convert .NET event's screen coordinates to client control 
   /// coordinates to be used by converted drag and drop members
   /// </summary>
   /// <param name="clientControl">Control to where the coordinates will be traslated</param>
   /// <param name="x">X Coordinate</param>
   /// <param name="y">Y Coordinate</param>
   public void ConvertCoordinatesToClient(Control clientControl, 
ref int x, ref int y)
   { 
      Point  convertedCoordinates = clientControl.PointToClient
(new Point(x,y));
      x = convertedCoordinates.X;
      y = convertedCoordinates.Y;
   }
}

3.3.5. Additional code for controls with no DragOver handlers in source

Add a .NET DragEnter event handler and add the following line of code

Visual Basic .NET

Private Sub theControl_DragEnter(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs) Handles theControl.DragEnter

   'UPGRADE_WARNING: The following statemente was inserted to allow this control to receive drag and drop actions 
   e.Effect = DragDropEffects.All

End Sub

C#

private void theControl_DragEnter(object sender, DragEventArgs e)
{
   //UPGRADE_WARNING: The following statement was inserted to allow this control to receive drag and drop actions
   e.Effect = DragDropEffects.All;
}

C# requires to register the event in the designer code

C#

this.theControl.DragEnter += new DragEventHandler(this.theControl_DragEnter);

3.4. OLEDragDrop event

This event is raised at the time the user releases the mouse button over a target, after a drag and drop operation.

3.4.1. Source code

Private Sub theControl_OLEDragDrop(Data As DataObject, Effect As Long, Button As Integer, Shift As Integer, X As Single, Y As Single)
   'User's code
   If Data.GetFormat(vbCFText) Then
      theControl.Text = Data.GetData(vbCFText)
   End If
   'End of user's code
End Sub

3.4.2. Expected code

The DataObject, Effect, Button, X and Y coordinates parameters are now contained by the DragEventArgs parameter. The conversion process should insert additional code inside the event handler to extract the required values being used by the user’s code. Conversion code for parameters not used in user’s code can be omitted.

Visual Basic .NET

Private Sub theControl _DragDrop(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs) Handles theControl.DragDrop
   Dim X As Single = e.X
   Dim Y As Single = e.Y
   Dim Button As Integer = e.KeyState \ &H100000
   Dim Shift As Integer = Control.ModifierKeys \ &H10000
   ConvertCoordinatesToClient(theControl, X, Y)
   'User's code
   If e.Data.GetDataPresent(DataFormats.Text) Then
      theControl.Text = CStr(e.Data.GetData(DataFormats.Text))
   End If
   'End of user's code

End Sub

C#

private void Text1_DragDrop(object sender, DragEventArgs e)
{   
   int X = e.X;
   int Y = e.Y;
   int Button = e.KeyState | 0x100000;
   int Shift = (int)Control.ModifierKeys | 0x10000;
   Support.ConvertCoordinatesToClient(Text1, ref X, ref Y);
   //User's code                    
   if (e.Data.GetDataPresent(DataFormats.Text))
   {
      Text1.Text = Convert.ToString(e.Data.GetData(DataFormats.Text));
   } 
   //End of user's code
}

Parameters mappings:

3.5. OLECompleteDrag

This event was raised to notify the source control when the drag-and-drop operation was complete. This was typically used to remove the data from the source for a cut and paste operation.

3.5.1 Source code

Private Sub theControl_OLECompleteDrag(Effect As Long)
  'Code to process the event
End Sub

3.5.2. Expected code

Visual Basic .NET

Private Sub theControl_OLECompleteDrag(ByVal Effect As Long)
  'Code to process the event
End Sub

C#

private void theControl_OLECompleteDrag(int Effect)
{
  //Code to process the event
}

Insert a call to the OLECompleteDrag method inside the OLEStartDrag method, just after the call to DoDragDrop method. Pass the Drag and Drop effect value returned by the DoDragDrop call.

Visual Basic .NET

Private Sub theControl_OLEStartDrag()
   Dim Effect As DragDropEffects
   Effect = theControl.DoDragDrop(theControl.SelectedText, DragDropEffects.Copy)
   
   'UPGRADE_WARNING: The following statement was inserted to support conversion of Drag and Drop
   theControl_OLECompleteDrag(Effect)

End Sub

C#

private void  theControl_OLEStartDrag( )
{
   DragDropEffects effect;
   effect = theControl.DoDragDrop(theControl.SelectedText, DragDropEffects.Copy);

   //UPGRADE_WARNING: The following statement was inserted to support conversion of Drag and Drop
   theControl_OLECompleteDrag((int)effect);
}

3.6. OLEGiveFeedback

This event is raised whenever the mouse passes over a possible target, during a drag and drop operation.

3.6.1. Source code

Private Sub theControl_OLEGiveFeedback(Effect As Long, DefaultCursors As Boolean)
    
   'User's code
    If Effect = vbDropEffectNone Then
        theControl.ForeColor = RGB(255, 0, 0)
    Else
        theControl.ForeColor = RGB(0, 0, 0)
    End If
    
    Dim defCursors As Boolean
    defCursors = DefaultCursors
   'End of user's code

End Sub

3.6.2. Expected code

To convert the GiveFeedback event handler, generate a .NET GiveFeedback event handler. References to Effect parameter must be changed to e.Effect and references to DefaultCursors parameter to e.UseDefaultCursors, with ‘e’ being the GiveFeedbackEventArgs parameter.

Visual Basic .NET

Private Sub theControl_GiveFeedback(ByVal sender As Object, ByVal e As GiveFeedbackEventArgs) Handles Text1.GiveFeedback

   'User's code 
   If e.Effect = DragDropEffects.None Then
      theControl.ForeColor = Color.FromArgb(255, 0, 0)
   Else
      theControl.ForeColor = Color.FromArgb(0, 0, 0)
   End If

   Dim defCursors As Boolean
   defCursors = e.UseDefaultCursors
   'End of user's code

End Sub

C#

private void theControl_GiveFeedback(object sender, GiveFeedbackEventArgs e)
{
   //User's code
   if (e.Effect == ((int)DragDropEffects.None))
   {
      theControl.ForeColor = Color.FromArgb(255, 0, 0);
   }
   else
   {
      theControl.ForeColor = Color.FromArgb(0, 0, 0);
   }

   bool defCursors;
   defCursors = e.UseDefaultCursors;
   //End of user's code
}

3.7. OLESetData

OLESetData event is fired when the drag and drop operation ends and the Data was not set in the OLEStartDrag event at the start of the drag and drop operation. This helps to delay the setting of the Data to whenever the programmer considers more appropiate.

Conversion and support for this event requires modifing the code inside the OLEStartDrag converted event, in order to pass some indicator of data not set yet to the target control’s DragDrop event handler.

3.7.1. Source code

Note the empty parameter in the SetData method inside OLEStartDrag event handler. It indicates that the Data will be set inside OLESetData event handler when another control asks for it calling the DataObject GetData method.

Private Sub theControl_OLESetData(Data As DataObject, DataFormat As Integer)
   If DataFormat = vbCFText Then
      Data.SetData "Text", vbCFText
   Else
      Data.SetData "RTF", vbCFRTF
   End If 
End Sub

Note the empty value parameter in the Data.SetData method call.

Private Sub theControl_OLEStartDrag(Data As DataObject, AllowedEffects As Long)
        Data.SetData , vbCFText
        AllowedEffects = vbDropEffectCopy
End Sub

3.7.2. Expected code

Asumming that the delayed data setting is not widely used, conversion process can use a simpler method to recover the functionality. Basically, the delayed setting feature will be removed and the data will be set since the start of the Drag and Drop operation.

It’s possible that in the OLESetData event handler, the Data to be set can change depending on the DataFormat value. This DataFormat is set in the GetData method at the end of the drag and drop operation, by the target control.

The best compromise is to assign the value corresponding to the same format set to the data object inside the OLEStartDrag event handler.

I.e., in the source code the data format set at the beginning (OLEStartDrag) is vbCFText, and the data parameter is empty. Later (in OLESetData), the data assignation will depend in the DataFormat parameter that could be vbCFText or vbCFRTF. Conversion process will choose the assignation corresponding to vbCFText (from OLEStartDrag) which is “SetData Text, vbCFText”, so the value to be set to the data object will be “Text”

The OLESetData method should be commented out, in case that the programmer needs to check anything of the original behavior of the code.

Visual Basic .NET

Private Sub Text1_OLEStartDrag()
   Dim Effect As DragDropEffects
   'Data.SetData(, vbCFText)
   'UPGRADE_WARNING: Drag and Drop delayed data setting behavior was removed.
   Effect = Text1.DoDragDrop("Text", DragDropEffects.Copy)
End Sub


'UPGRADE_WARNING: Drag and Drop delayed data setting behavior was removed.
'Private Sub Text1_OLESetData(ByRef Data As DataObject, ByRef DataFormat As Short)
'    If DataFormat = vbCFText Then
'           Data.SetData("Text", vbCFText)
'       Else
'           Data.SetData("RTF", vbCFRTF)
'       End If
'End Sub

C#

private void Text2_OLEStartDrag()
{
   DragDropEffects effect;
   //Data.SetData( , vbCFText);
   //AllowedEffects = (int) DragDropEffects.Copy;
                
   //UPGRADE_WARNING: Drag and Drop delayed data setting behavior was removed.    
   effect = Text2.DoDragDrop("Text", DragDropEffects.Copy);
   Text2_OLECompleteDrag((int)effect);
}

//UPGRADE_WARNING: Drag and Drop delayed data setting behavior was removed.            
//private void  Text2_OLESetData( DataObject Data,  short DataFormat)
//{
//    if ( DataFormat = vbCFText ) 
//    {
//        Data.SetData("Text", vbCFText);
//    }
//    else
//    {
//        Data.SetData("RTF", vbCFRTF);
//    }
//}

3.8. Conversion of constants for OLE drag and drop

VB6 format constants can be converted to System.Windows.Forms.DataFormats constants.

Table 1. Equivalences of format constants.

VB6 drag and drop constants can be converted to System.Windows.Forms.DragDropEffects constants.

Table2. Equivalences for allowed drag and drop effects constants

3.9. Additional mappings to support conversion

VB6 drag and drop uses a DataObject object to pass all the data and information used by the drag and drop operation as a parameter to all events. .NET uses a similar approach but the DataObject object is encapsulated inside the DragEventArgs parameter of the events.

* Conversion of DataObject.SetData needs a special conversion when starting a drag and drop action as described in sections 3.2.1.

3.10. DragMode property

3.10.1. Source code

Automatic drag mode allows the whole control or its contents to be dragged. This feature is not supported in .NET.

theControl.OLEDragMode = vbAutomatic

VB6 Manual drag mode requires to code all the drag and drop handling. This is the same as .NET drag and drop.

theControl.OLEDragMode = vbManual

3.10.2. Expected code

Automatic drag and drop is not supported in .NET

Visual Basic .NET

'UPGRADE_WARNING: Control.DragMode was not upgraded.
'theControl.OLEDragMode = vbAutomatic

C#

//UPGRADE_WARNING: Control.DragMode was not upgraded.
//theControl.OLEDragMode = vbAutomatic

Manual drag and mode is the default behavior of .NET drag and drop. All drag and drop handling must be coded.

Visual Basic .NET

'UPGRADE_WARNING: Control.DragMode was not upgraded.
'theControl.OLEDragMode = vbManual

C#

//UPGRADE_WARNING: Control.DragMode was not upgraded.
//theControl.OLEDragMode = vbManual

See also:

• 1. VB6 Drag and Drop Overview
• 2. Conversion of Standard Drag and Drop
• 3. Conversion of manual OLE Drag and Drop
• Return Drag and Drop Conversion Steps Contents