Implementing the Drag-Drop Protocol

• Microsoft Windows Software Development Kit (SDK) for Windows version 3.1

SUMMARY

Windows 3.1 supports four new functions and one new message that enable an application to implement the drag-drop protocol. DRAGDROP is a file in the Software/Data Library that demonstrates using all four functions and the message. When the user drags and drops a file onto DRAGDROP, the name of the file is added to a list box in DRAGDROP.

Download DRAGDROP.EXE from the Microsoft Software Library (MSL) on the following services:

• Microsoft Download Service (MSDL)

        Dial (206) 936-6735 to connect to MSDL
        Download DRAGDROP.EXE (size: 20399 bytes) 
  

• Internet (anonymous FTP)

        ftp ftp.microsoft.com
        Change to the \SOFTLIB\MSLFILES directory
        Get DRAGDROP.EXE (size: 20399 bytes) 
  

MORE INFORMATION

An application that can accept files dragged from the File Manager calls the DragAcceptFiles function specifying one or more of its windows. When the user drags a file from the File Manager into the window specified in the DragAcceptFiles call, and releases the left mouse button, File Manager sends the application a WM_DROPFILES message. (File Manager sends a WM_DROPFILES message only to applications that have registered a window with DragAcceptFiles.)

One of the parameters to WM_DROPFILES contains a handle to an internal data structure. The DragQueryFile function retrieves a number of dropped files and their names from the data structure and returns this information to the application. Likewise, DragQueryPoint retrieves the position of the mouse cursor when the file(s) was dropped.

To release the memory allocated by Windows for the WM_DROPFILES data structure, the application must call the DragFinish function after it retrieves the applicable data.