fTWUCallback

The fTWUCallback typedef defines the callback function prototype used as a general event/progress callback. The actual callback function may have any valid C/C++ name, but it must follow the prototype defined by the fTWUCallback typedef.

typedef URESULT (*fTWUCallback)(
    TWUHANDLE hSession,
    int nEventCode,
    const TCHAR *pszEventMsg,
    UINT64 ulProgress,
    UINT64 ulTotal,
    LPARAM lCookie
);

Delphi version:

type fTWUCallback = function(
    hSession: TWUHANDLE;
    nEventCode: Integer;
    pszEventMessage: PTCHAR;
    ulProgress: UINT64;
    ulTotal: UINT64;
    lCookie: LPARAM
): URESULT;

Parameters

hSession

[Input] Handle to an open TWU session.

nEventCode

[Input] One of the event codes as defined in Callback events below.

pszEventMsg

[Input] Pointer to a 0-terminated string that describes the event in a user-friendly way. Your callback function may use this string for display in its user interface.

From release 3.3.2435 onwards, this parameter may contain additional strings that provide raw information about the event, for example a URL or file path. Use the TWUGetEventArg function to access the additional information, as in TWUGetEventArg(pszEventMsg, 0). See Callback events below for a per-event list of additional information.

ulProgress

[Input] Amount of progress made towards the total size given by ulTotal, or 0 if no progress amount is available or applicable. Your callback function may use this value to update a progress bar or something similar.

ulTotal

[Input] Total size or amount of work to do in the current operation, or 0 if the total is not available. During download progress events (TWU_CBEVENT_DOWNLOAD_PROGRESS, see below), both ulProgress and ulTotal are expressed in bytes, if the sizes are available.

lCookie

[Input] User-defined value that was passed in to TWUOpenSession, TWUOpenUpdateURL, or TWURegisterCallback. You can use this cookie to pass additional information to the callback function.

Return value

If the function succeeds, it must return ERROR_SUCCESS (0) to continue the operation. If it fails or if you want to terminate the operation for some reason, the function must return a nonzero Win32 error code. In that case, the operation will be terminated as soon as possible.

Note: Some events ignore the return code; see the table below.

Callback events

The following table defines the callback events passed to the callback function. Events marked * ignore the callback's return code. Unless otherwise noted, the event has no additional arguments.