Drag and Drop in a Dialog

• Download demo project - 4.66 KB
• Download source - 15.6 KB

Introduction

Here is a simple method to have a Drag and Drop feature in your dialog based applications. To provide Drag and Drop we have a Windows Message Handler called WM_DROPFILES. Handle this message through the ON_MESSAGE message map to capture the dropped files.

Message Handler

//
 BEGIN_MESSAGE_MAP(CComGuidFinderDlg, CDialog)
  //{{AFX_MSG_MAP(CComGuidFinderDlg)
  ON_WM_PAINT()
  ON_WM_LBUTTONDOWN()
  ON_MESSAGE(WM_DROPFILES,OnDropFiles)// Message Handler for Drang and Drop
  //}}AFX_MSG_MAP
END_MESSAGE_MAP()
//

Now it is time to handle the WM_DROPFILES messages through a user defined method. The function prototype should be like this:

LRESULT  OnDropFiles(WPARAM wParam,LPARAM lParam);

Finally we have a function to capture the drop events. wParam is a handle to the HDROP structure describing the dropped files. To get info about the dropped file, i.e., the file name used:

DragQueryFile(hDrop,    // Struture Identifier
        -1,        // -1 to Drop more than one file or ( integer 0 to max )
                   // to drop selected No of files
        szDroppedFile,// Droped File Name
        MAX_PATH);   // Max char

So now we have done all possible coding in our dialog based application to handle the Drag & Drop feature. But still it is handicapped. Handling the Drop event is not enough to ensure the Drag & Drop feature. We need to register our window to accept the dropped file using:

BOOL CComGuidFinderDlg::OnInitDialog()
{
  ......
  .....
  DragAcceptFiles(TRUE) // To Accept Dropped file Set this TRUE
}

Good... That's all, and we have done well!

I added one more feature in this sample, i.e., moving our dialog by clicking on anywhere on the window. This can be done by posting the WM_NCLBUTTONDOWN message to HTCAPTION handle this statement in OnLButtonDownMessage(...) .

PostMessage(WM_NCLBUTTONDOWN,HTCAPTION,MAKELPARAM(point.x,point.y))