Detect Dragging File event before Dropped on Form

Question

I'm trying to create an application for Windows. In my application, when dragging items File from Windows Explorer to FormOne and then FormOne will call FormSecond show and Drop Items on FormSecond. My proplem is: I wrote code for FormSecond to handle received Files is Fine. But on FormOne I don't know how to catch dragging event mouse on FormOne to show FormSecond.

Everybody can help me, please!!! Sorry, my English is not good!

Answer 1

When the user drags files from Windows Explorer onto a TForm, there are two different ways to handle the drop:

1. Have the Form either:

   • override the virtual CreateWnd() method to call DragAcceptFiles(), or:

   • override the virtual CreateParams() method to enable the WS_EX_ACCEPTFILES window style.

   And then have the Form catch the WM_DROPFILES window message. The message's wParam value is an HDROP handle that you can pass to the DragQueryFile(), DragQueryPoint(), and DragFinish() APIs.

2. Write a class that implements the IDropTarget interface, implementing the various Drag(Enter|Over|Leave)() and Drop() methods to query the file information from the provided IDataObject. Then have the Form pass an instance of that class to RegisterDragDrop(). See Transferring Shell Objects with Drag-and-Drop and the Clipboard for more details.