A Generic IDropTarget COM Class for Dropped Text

This article is part of the drag and drop interface samples.

1. Serializing ASCII Data
2. Modeless child dialog
3. Modeless sibling dialog
4. The drag source
5. The MFC drop target
6. The TBTextTarget class

• Download source files - 23.9 KB

Doing It the OLE Way... An Interface Class to Derive From

If you are a MFC purist and only want to have CObject derived classes in your project, then consider the pure MFC drop target.

You will find the sample project in step3generic or you may download only the TBTextTarget class.

A Generic IDropTarget COM Class for Dropped Text

I promised you "a better way" and I fulfill this promise now - at least half of it because it's for the drop target, the IDropSource and IDataObject parts are missing, but the MFC support for the begin of dragging out of CListCtrl is quite good (perhaps someone else can take this as an exercise and place these wrappers in the comments for this article. :)

The OLE docs say: "If you want your (window) class to be drop-enabled, implement a IDropTarget interface." Nice - what's that? In plain English, I'd say: your drop-enabled class needs a couple of functions which do the right things. The bundle of these functions make out "the interface" and because some interfaces are "at the top" of others, you have - a kind of class hierarchy!

Due to the fact that we are talking about text dragging the private data format described in the other articles of this series. Implement the drag sources as common interface (CF_TEXT, see "Data is going abroad...") for the drop part and do the following (and compare with the pure MFC stuff!)

1. Create your CWnd-based class (CYourClass, e.g. your dialog) as usual.
2. Include the files TBTextTarget.h and TBTextTarget.cpp in your project.
3. Go to the class definition of CYourClass and derive it from TBTextTarget too: e.g., the line...
   C++

   class CDropDialog : public CDialog 

   ...will become:
   C++

   class CDropDialog : public CDialog, TBTextTarget 

4. Don't forget to #include "TBTextTarget.h"
5. At a point where this window is created (for example: OnInitDialog is great), tell Windows that you are drag&drop-enabled:
   C++

   BOOL CDropDialog::OnInitDialog()
       {
           CDialog::OnInitDialog();
           ::RegisterDragDrop(GetSafeHwnd(), this);
           // the other stuff follows ....
       }

6. Add this function to CYourClass (it's pure virtual in TBTextTarget because it depends on YOU what you do with YOUR data):
   C++

   void ProcessData(CString Data)

   This function will be called when a text was dragged into your window. Do with it whatever you like (or need). For example:

   C++

   CDropDialog::ProcessData(CString Data)
   {
      CString t1(Data), t2;
      int idx = t1.Find('\n');
   
      while (idx !=-1)
      {
         t2 = t1.Left(idx);
         t1 = t1.Mid(idx+1);
         InsertRow(t2);
         idx = t1.Find('\n');
      }
   }   

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