Drag&Drop Files into Game possible?

Development Programming & Scripting
1

Hi,

I have to make my game’s window capable of reacting to drag&drop operations coming from the outside of the application (especially windows), like dragging a png-file from my desktop into my application (e.g. to be able to get its filepath).

I successfully tried adding an IWindowsMessageHandler to my FWindowsApplication in c++ but this does not seem to be the right way since I can’t get any useful information out of it.

DropMessageHandler = FDropMessageHandler();
FWindowsApplication* WindowsApplication = (FWindowsApplication*)GenericApplication.Get();
WindowsApplication->AddMessageHandler(DropMessageHandler);

class FDropMessageHandler
: public IWindowsMessageHandler
{

public:

virtual bool ProcessMessage(HWND hwnd, uint32 msg, WPARAM wParam, LPARAM lParam, int32& OutResult) override
{

//If right approach, what to do here?

return true;

}
};

Am I missing something with the MessageHandler or is there any other way to solve my problem?

2

I solved the problem myself. I already had the right approach and this is how I got it working:

#include "AllowWindowsPlatformTypes.h"
#include "shellapi.h"
#include "HideWindowsPlatformTypes.h"

class FDropMessageHandler : public IWindowsMessageHandler { 
public:

virtual bool ProcessMessage(HWND hwnd, uint32 msg, WPARAM wParam, LPARAM lParam, int32& OutResult) override {

int32 NumFiles;
HDROP hDrop;
TCHAR NextFile[MAX_PATH];

if (msg == WM_DROPFILES)
	{
		hDrop = (HDROP)wParam;
		// Get the # of files being dropped.
		NumFiles = DragQueryFile(hDrop, -1, NULL, 0);

		for (int32 File = 0; File < NumFiles; File++)
		{
			// Get the next filename from the HDROP info.
			if (DragQueryFile(hDrop, File, NextFile, MAX_PATH) > 0)
			{
				FString Filepath = NextFile;
               //Do whatever you want with the filepath
			}
		}
	}    
return true; 
}
 };

The DragQueryFile function that gives me the information i need is only available if the shellapi.h is included.
This is only for Windows, make shure you surround all the platform specific code with #if PLATFORM_WINDOWS … #endif

1 Like
3

I think that this is a decent solution since we do not have platform-agnostic code for drag & drop in runtime modules yet. I referenced it in a related tutorial.

4

@MBatzdorf Hi, I’m following your solution, but the event WM_DROPFILES doesn’t show up anytime (I am printing all of them, and I get, WM_WINDOWPOSCHANGED, WM_MOVING and stuff like that, but no WM_DROPFILES).

I have tried to enable the event using ChangeWindowMessageFilter, but it doesn’t work either (don’t know if I am doing it properly)

Also, when I drag something into the window, the mousse pointer changes to a circle with a bar crossing it, stating (I guess) that you can’t do that action.

How did you get it working?

Thanks in advance!!

5

Bump! I’m at the same point as havidarou. The mouse pointer changes to the crossed cricle and a WM_DROPFILES Message doesn’t show up… Any progress since the last year at this?

6

Y’all need to add:
HWND hwndd = GetActiveWindow();
DragAcceptFiles(hwndd, true);
when adding the message handler to the FWindowsApplication

Peace and love :slight_smile:

7

Here is how you get the PlatformApplication.
Don’t forget to unregister the handle!

        FSlateApplication& slateApp = FSlateApplication::Get();
        TSharedPtr<class GenericApplication> platformApp = slateApp.GetPlatformApplication();
        if (platformApp.IsValid())
        {
#if PLATFORM_WINDOWS
... do your stuff
#endif // PLATFORM_WINDOWS
        }

And you should not return true always!
Return true only when the message was handled!