main.cpp

//
//	MAIN.CPP
//
//	DragSource 
//
//	Freeware written by J Brown 2004
//
//	www.catch22.net
//

#define STRICT

#include <windows.h>
#include "resource.h"

#define APPNAME "IDropSource"

#pragma comment(linker, "/OPT:NOWIN98")

HWND hwndMain;
HWND hwndEdit;
HINSTANCE hInstance;

WNDPROC OldEditWndProc;

HRESULT CreateDropSource(IDropSource **ppDropSource);

HRESULT CreateDataObject(FORMATETC *fmtetc, STGMEDIUM *stgmeds, UINT count, IDataObject **ppDataObject);

//
//	Is the mouse cursor within the edit control's selected text?
//
//	Return TRUE/FALSE 
//
BOOL MouseInSelection(HWND hwndEdit, LPARAM MouseMsgParam) {
    DWORD nSelStart;
    DWORD nSelEnd;

    // get the selection inside the edit control
    SendMessage(hwndEdit, EM_GETSEL, (WPARAM) &nSelStart, (LPARAM) &nSelEnd);

    if (nSelStart != nSelEnd) {
        DWORD nCurPos;

        // Get the cursor position the mouse has clicked on
        nCurPos = SendMessage(hwndEdit, EM_CHARFROMPOS, 0, MouseMsgParam);
        nCurPos = LOWORD(nCurPos);

        // Did the mouse click inside the active selection?
        return (nCurPos >= nSelStart && nCurPos < nSelEnd) ? TRUE : FALSE;
    }

    return FALSE;
}

//
//	Remove any selection from the edit control
//
void ClearSelection(HWND hwndEdit) {
    SendMessage(hwndEdit, EM_SETSEL, -1, -1);
}

//
//	Copy selected text to a HGLOBAL and return it
//
HGLOBAL CopySelection(HWND hwndEdit) {
    DWORD nSelStart, nSelEnd;
    DWORD nSelLength, nEditLength;
    HGLOBAL hMem;
    char *ptr;
    char *tmp;

    SendMessage(hwndEdit, EM_GETSEL, (WPARAM) &nSelStart, (LPARAM) &nSelEnd);

    nSelLength = nSelEnd - nSelStart;

    // get the entire contents of the control
    nEditLength = SendMessage(hwndEdit, EM_GETLIMITTEXT, 0, 0);
    tmp = (char *) malloc(nEditLength);

    SendMessage(hwndEdit, WM_GETTEXT, nEditLength, (LPARAM) tmp);

    hMem = GlobalAlloc(GHND, nSelLength + 1);
    ptr = (char *) GlobalLock(hMem);

    // copy the selected text and nul-terminate
    memcpy(ptr, tmp + nSelStart, nSelLength);
    ptr[nSelLength] = '\0';

    GlobalUnlock(hMem);

    free(tmp);

    return hMem;
}

//
//	Subclass window-procedure for EDIT control
//
LRESULT CALLBACK EditWndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) {
    static BOOL fMouseDown = FALSE;
    static BOOL fDidDragDrop = FALSE;

    switch (msg) {
        case WM_KEYDOWN:

            // when ESCAPE is pressed clear the current selection
            if (wParam == VK_ESCAPE)
                ClearSelection(hwnd);

            break;

        case WM_LBUTTONDOWN:
        case WM_LBUTTONDBLCLK:

            // if the mouse is pressed when it is over a selection,
            // then start a drag-drop as soon as the mouse moves next
            if (MouseInSelection(hwndEdit, lParam)) {
                fMouseDown = TRUE;
                fDidDragDrop = FALSE;
                SetCapture(hwnd);
                return 0;
            }

            break;

        case WM_SETCURSOR:

            // set the mouse cursor to an ARROW when it intersects the
            // current selection, or the default IBEAM otherwise
            if ((HWND) wParam == hwnd) {
                POINT pt;
                GetCursorPos(&pt);
                ScreenToClient(hwndEdit, &pt);

                if (MouseInSelection(hwndEdit, MAKELPARAM(pt.x, pt.y))) {
                    SetCursor(LoadCursor(0, (IDC_ARROW)));
                } else {
                    SetCursor(LoadCursor(0, (IDC_IBEAM)));
                }
            }

            return TRUE;

        case WM_MOUSEMOVE:

            // if the mouse is held down then start a drag-drop
            if (fMouseDown) {
                IDataObject *pDataObject;
                IDropSource *pDropSource;
                DWORD dwEffect;
                DWORD dwResult;

                FORMATETC fmtetc = {CF_TEXT, 0, DVASPECT_CONTENT, -1, TYMED_HGLOBAL};
                STGMEDIUM stgmed = {TYMED_HGLOBAL, {0}, 0};

                // transfer the current selection into the IDataObject
                stgmed.hGlobal = CopySelection(hwndEdit);

                // Create IDataObject and IDropSource COM objects
                CreateDropSource(&pDropSource);
                CreateDataObject(&fmtetc, &stgmed, 1, &pDataObject);

                //
                //	** ** ** The drag-drop operation starts here! ** ** **
                //
                dwResult = DoDragDrop(pDataObject, pDropSource, DROPEFFECT_COPY | DROPEFFECT_MOVE, &dwEffect);

                // success!
                if (dwResult == DRAGDROP_S_DROP) {
                    if (dwEffect & DROPEFFECT_MOVE) {
                        // remove selection from edit control
                    }
                }
                    // cancelled
                else if (dwResult == DRAGDROP_S_CANCEL) {
                }

                pDataObject->Release();
                pDropSource->Release();

                ReleaseCapture();
                fMouseDown = FALSE;
                fDidDragDrop = TRUE;
            }

            break;

        case WM_LBUTTONUP:

            // stop drag-drop from happening when the mouse is released.
            if (fMouseDown) {
                ReleaseCapture();
                fMouseDown = FALSE;

                if (fDidDragDrop == FALSE)
                    ClearSelection(hwnd);
            }

            break;
    }

    return CallWindowProc(OldEditWndProc, hwnd, msg, wParam, lParam);
}

//
//	Main Window message handler
//
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) {
    switch (msg) {
        case WM_CREATE:

            // create a child-window EDIT control
            hwndEdit = CreateWindowEx(WS_EX_CLIENTEDGE, "EDIT", "",
                                      WS_CHILD | WS_VISIBLE | ES_MULTILINE | ES_WANTRETURN | WS_VSCROLL,
                                      0, 0, 0, 0, hwnd, 0, hInstance, 0);

            // fixed-width font
            SendMessage(hwndEdit, WM_SETFONT, (WPARAM) GetStockObject(ANSI_FIXED_FONT), 0);

            // subclass the edit control so we can add drag+drop support to it
            OldEditWndProc = (WNDPROC) SetWindowLongPtr(hwndEdit, GWLP_WNDPROC,
                                                        reinterpret_cast<LONG_PTR>(EditWndProc));

            SetFocus(hwndEdit);

            return TRUE;

        case WM_COMMAND:

            // react to menu messages
            switch (LOWORD(wParam)) {
                case IDM_FILE_EXIT:
                    CloseWindow(hwnd);
                    return 0;

                case IDM_FILE_ABOUT:
                    MessageBox(hwnd, "IDropSource Test Application\r\n\r\n"
                                     "Copyright(c) 2004 by Catch22 Productions\t\r\n"
                                     "Written by J Brown.\r\n\r\n"
                                     "Homepage at www.catch22.net", APPNAME, MB_ICONINFORMATION);
                    return 0;
            }

            break;

        case WM_CLOSE:

            // shut program down
            DestroyWindow(hwnd);
            PostQuitMessage(0);
            return 0;

        case WM_SIZE:

            // resize editbox to fit in main window
            MoveWindow(hwndEdit, 0, 0, LOWORD(lParam), HIWORD(lParam), TRUE);
            return 0;
    }

    return DefWindowProc(hwnd, msg, wParam, lParam);
}

void InitMainWnd() {
    WNDCLASSEX wc = {sizeof(wc)};

    wc.lpfnWndProc = WndProc;
    wc.lpszClassName = APPNAME;
    wc.lpszMenuName = MAKEINTRESOURCE(IDR_MENU1);
    wc.hInstance = hInstance;

    RegisterClassEx(&wc);
}

void CreateMainWnd() {
    hwndMain = CreateWindowEx(0, APPNAME, APPNAME,
                              WS_VISIBLE | WS_OVERLAPPEDWINDOW,
                              CW_USEDEFAULT, CW_USEDEFAULT, 512, 200, 0, 0,
                              hInstance, 0);
}

int WINAPI WinMain(HINSTANCE hInst, HINSTANCE hPrev, LPSTR lpCmdLine, int nShowCmd) {
    MSG msg;

    hInstance = hInst;

    // This program requires COM
    OleInitialize(0);

    InitMainWnd();
    CreateMainWnd();

    // message-pump
    while (GetMessage(&msg, 0, 0, 0)) {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    // Shutdown COM
    OleUninitialize();

    return 0;
}