TWebBrowser OLE Drag Drop

Posted on 2004-09-09
Last Modified: 2010-04-05
How do I override the default OLE drag drop behaviour for a TWebBrowser?

I am using the TWebrowser component as a HTML editor by putting it in edit mode.  I like the fact that I can drag HTML from IE into it. But, When I drag a link, or a html file, it opens the document, replacing the contents with the new file.  I would like to speficy my own behaviour when files are dropped, but use the existing behaviour when html is dropped.

It looks like I need to create a new Interface that inherits from the IDropTarget Interface that TWebBrowser uses, but I have no Idea how to do this.

I have figured out how to replace the IDropTarget interface, by doing the following:

CustDoc: ICustomDoc;
hr : HResult;
  hr := WebBrowser1.Document.QueryInterface(ICustomDoc, CustDoc);
  if hr = $00000000 {S_OK} then

DocHostUIHandler is an instance of this class, which allows overriding the regular UI operations:

TDocHostUIHandler = class(TComObject, IDocHostUIHandler)

One of the methods of this class is GetDropTarget, which allows you to specify an alternate IDropTarget interface.  I have been able
disable and enable drag drop by editing the contents.  So, I think that all I need to do is replace ppDropTarget with my own interface? How do I create this interface, so that I can inherit some of the existing behaviour?

function TDocHostUIHandler.IDocHostUIHandler_GetDropTarget(const pDropTarget: IDropTarget;
  out ppDropTarget: IDropTarget): HRESULT;
 //Enables Drag drop;
  Result := S_OK;
  //Disables drop
  //Result := S_FALSE;

Question by:wolsen
1 Comment
LVL 33

Accepted Solution

Slick812 earned 125 total points
Comment Utility
hello  wolsen, , I have done a little with the IDropTarget Interface, I am mostly posting here because no one else has. I can not explain the IDropTarget Interface since, there are many factors and methods, it controls the cursors shown for a drag over, and queries for drop data types that are accepted or not, I do not handle any of that in my code. . .
Here is a BASIC and about as simple as you can get IDropTarget class. . . There are MANY types of Drop Data, they are usually typed by a Clip board format, like CF_HDROP  , CF_TEXT  and  CF_IDLIST , I do not know the CF_  type for HTML or Links . . .
The following code only does the CF_HDROP  format, sorry I do not have time now to clean it up , (take out un-used code) - -


  TDropTarget = class(TInterfacedObject, IDropTarget)
   function DragEnter(const DataObj: IDataObject; grfKeyState: Integer; pt: TPoint; var dwEffect: Integer): HResult; stdcall;
   function DragOver(grfKeyState: Integer; pt: TPoint; var dwEffect: Integer): HResult; stdcall;
   function DragLeave: HResult; stdcall;
   function Drop(const DataObj: IDataObject; grfKeyState: Integer; pt: TPoint; var dwEffect: Integer): HResult; stdcall;


// TDropTarget = = = = = = = = = = = = = = = = = = = = = = = =
// the first three functions do not do anything, just return a default NOERROR and the system does the default handling

function TDropTarget.DragEnter(const DataObj: IDataObject; grfKeyState: Longint;
                               pt: TPoint; var dwEffect: Longint): HResult;
//DataObj.EnumFormatEtc(dwDuirection, IEnumFormatetc);
 Result := NOERROR;

function TDropTarget.DragOver(grfKeyState: Longint; pt: TPoint;
                              var dwEffect: Longint): HResult;
 Result := NOERROR;

function TDropTarget.DragLeave: HResult;
 Result := NOERROR;

function TDropTarget.Drop(const DataObj: IDataObject; grfKeyState: Longint;
                          pt: TPoint; var dwEffect: Longint): HResult;
 Enum : IEnumFormatEtc;
 Link : PChar;
 Dummy : Integer;
 Format : TFormatEtc;
 Medium : TStgMedium;
 {FileStr,} FileStr1: String;
 DropFiles: PDropFiles;
 //ShiftState: Byte;

  {function GetFilesFromHGlobal(const HGlob: HGlobal; Files: String): boolean;
  DropFiles: PDropFiles;
  Filename: PChar;
  DropFiles := PDropFiles(GlobalLock(HGlob));
  Files := 'Low';
  //FileStr1 := 'Low';
    Filename := PChar(DropFiles) + DropFiles^.pFiles;
    while (Filename^ <> #0) do
      if (DropFiles^.fWide) then // -> NT4 & Asian compatibility
        Files := Files+','+PWideChar(FileName);
        inc(Filename, (Length(PWideChar(FileName)) + 1) * 2);
      end else
        Files := Files+','+FileName;
        FileStr1 := FileStr1 +','+FileName;
        inc(Filename, Length(Filename) + 1);

  Result := (Length(Files) > 0);

{function KeysToShiftState(Keys: Word): Byte;
// did not need key dowm info
  Result := Zero;
  if Keys and MK_SHIFT <> Zero then Result := One;
  if Keys and MK_CONTROL <> Zero then Result := Result or 2;
  if Keys and MK_LBUTTON <> Zero then Result := Result or 4;
  if Keys and MK_RBUTTON <> Zero then Result := Result or 8;
  if Keys and MK_MBUTTON <> Zero then Result := Result or 16;
  //if GetKeyState(VK_MENU) < 0 then Result := Result or 32;

{this does very little, just gets the file name from the DropFiles, a pointer to
 the TDropFiles in ShlObj.pas  , I only needed a single file name, I only do ONE kind
 of drop data, CF_HDROP, but there are many more}

Result := S_OK;

if DataObj.EnumFormatEtc(DATADIR_GET, Enum) <> S_OK then Exit;

 while Enum.Next(One, Format, @Dummy) = S_OK do
 begin // Enum.Next
 //ComStr := ComStr+' '+ Int2Str(Format.cfFormat);
 //SetWindowText(hWordEdit, Pchar(ComStr));

 if Format.cfFormat = CF_HDROP then
   if DataObj.GetData(Format, Medium) = S_OK then
     begin  // GetData
     //ShiftState := KeysToShiftState(grfKeyState);
      if (medium.tymed = TYMED_HGLOBAL) then
        begin // TYMED_HGLOBAL
       //GetFilesFromHGlobal(medium.HGlobal, FileStr);
       DropFiles := PDropFiles(GlobalLock(medium.HGlobal));
       Link := PChar(DropFiles) + DropFiles^.pFiles;
       while (Link^ <> #0) do
         begin // Link <> 0
         if (DropFiles^.fWide) then // -> NT4 & Asian compatibility
           begin // fWide
           FileStr1 := FileStr1+PWideChar(Link);
           inc(Link, (Length(PWideChar(Link)) + One) * Two);
           end else // fWide
           FileStr1 := FileStr1 +Link;
           inc(Link, PCharLength(Link) + One);
           end; // else fWide
         end; // Link <> 0

       end; // TYMED_HGLOBAL
      //Don't forget to clean-up!
      end; // finally
     end;  // GetData
  if Length(FileStr1) > 6 then
    if FileExists(FileStr1) then
    if LoadIColFile(FileStr1) > mOne then
 end; // Enum.Next


// TDropTarget finish  = = = = = = = = = =  = =

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

I have no Idea how to incorperate this in to a web browser for editing, and know nothing about the  IDocHostUIHandler_GetDropTarge  function. . ,
I use this code to give my API custom control drop file handling -

DropTar: TDropTarget;

if OleInitialize(nil) = S_OK then
  RegisterDragDrop(hScrollGrid, DropTar);
// hScrollGrid is the control Handle

- - - - - - - - - - - - - - - - - - - -

there is also an API function  RevokeDragDrop( ) which will Turn OFF the IDropTarget Interface for a control, I do not have time to try it, but you may be able to change the IDtopTarget for your window with -

RegisterDragDrop(WebBrowser.Handle, DropTar);

but there may be complications with an application as complex as the IE browser!, , like I said I have not tried it.

also, I wonder if you know of the ActiveX control DHTMLEdit, which is a system activeX that is for HTML Editing, and is in the  DHTMLEDLib_TLB.pas and is suppose to be good for an HTML editor, if you can figure out how to use it

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