Using the Drag-Drop Feature

When an application implements the drag-drop feature, a user can select one or more files in File Manager, drag them to an open application, and drop them there. The application in which the files were dropped receives a message it can use to retrieve the filenames and the coordinates of the point at which the files were dropped.

An application that can accept dropped files from File Manager calls the DragAcceptFiles function for one or more of its windows. When the user releases the mouse button to drop a file or files in the window specified in the call to DragAcceptFiles, File Manager sends the application a WM_DROPFILES message. (File Manager does not send the WM_DROPFILES message to an application unless the application calls DragAcceptFiles.) WM_DROPFILES contains a handle of a structure the application can query to retrieve the name of the dropped file and the coordinates of the cursor when the file was dropped. The application can use the DragQueryFile function to retrieve a count of the files that were dropped and their names. The DragQueryPoint function returns the window coordinates of the cursor when the user released the mouse button.

To free the memory allocated by the system for the WM_DROPFILES message, an application calls the DragFinish function when it is finished.

For example, an application can call the DragAcceptFiles function when it starts and call a drag-drop function when it receives a WM_DROPFILES message, as shown in the following example.

case WM_CREATE:

DragAcceptFiles(hwnd, TRUE);

break;

case WM_DROPFILES:

DragFunc(hwnd, wParam); /* application-defined function */

break;

case WM_DESTROY:

DragAcceptFiles(hwnd, FALSE);

break;

The following example uses the DragQueryPoint function to determine where to begin to write text. The first call to the DragQueryFile function determines the number of dropped files. The loop writes the name of each file, beginning at the point returned by DragQueryPoint.

POINT pt;

WORD cFiles, a;

char lpszFile[80];

DragQueryPoint((HANDLE) wParam, &pt);

cFiles = DragQueryFile((HANDLE) wParam, 0xFFFF, (LPSTR) NULL, 0);

for(a = 0; a < cFiles; pt.y += 20, a++) {

DragQueryFile((HANDLE) wParam, a, lpszFile, sizeof(lpszFile));

TextOut(hdc, pt.x, pt.y, lpszFile, lstrlen(lpszFile));

}

DragFinish((HANDLE) wParam);

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