Pass user data at window creation

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  • Pass user data at window creation

    Hello,

    I would like to encapsulate a view that contains a window and some widget in a class. So I started with something like below :

    C Source Code

    1. /// --- view.hpp
    3. class View
    4. {
    5. public:
    6. void create();
    8. private:
    10. static void internal_callback(WM_MESSAGE* pMsg);
    11. void callback(WM_MESSAGE * pMsg);
    13. WM_HWIN win_;
    14. };
    16. /// --- view.cpp
    18. void View::create()
    19. {
    20. win_ = WM_CreateWindowAsChild(0, 0, 240, 160, WM_HBKWIN, WM_CF_SHOW, View::internal_callback,
    21. sizeof(this));
    23. WM_SetUserData(win_, this, sizeof(this));
    24. }
    26. void View::internal_callback(WM_MESSAGE* pMsg)
    27. {
    28. /// I need to test this because SetUserData is call after creation
    29. /// So it avoids NULL pointer
    30. if (pMsg->MsgId == WM_CREATE)
    31. {
    32. /// Use static members...
    33. }
    34. else
    35. {
    36. void* view = NULL;
    37. WM_GetUserData(pMsg->hWin, view, 4); /// I can't call sizeof(this) but I know it is 4
    39. if (view != NULL) /// !!! view is always NULL
    40. {
    41. static_cast<View*>(view)->callback(pMsg);
    42. }
    43. }
    44. }
    46. void View::callback(WM_MESSAGE * pMsg)
    47. {
    48. switch (pMsg->MsgId)
    49. {
    50. case WM_PAINT:
    51. {
    52. GUI_SetBkColor(GUI_WHITE);
    53. GUI_Clear();
    55. GUI_SetColor(GUI_BLACK);
    56. GUI_DispString("Hello World");
    57. break;
    58. }
    59. default:
    60. WM_DefaultProc(pMsg);
    61. break;
    62. }
    63. }
    Display All


    So I have two questions:

    - Does anyone knows why view is always equal to NULL after a call to WM_GetUserData() to retrieve a pointer to "this" ?

    - Is there a way to pass a user_data at construction and not after with a setter to avoid to check for WM_CREATE in internal_callback() ?

    Thanks a lot,
    Regards,

    Nicolas