C# Definition:

    [Guid("148BD52B-A2AB-11CE-B11F-00AA00530503"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    public interface ITaskTrigger
    {
    int SetTrigger( ref TASK_TRIGGER pTrigger);
    int GetTrigger( ref TASK_TRIGGER pTrigger);
    int GetTriggerString([MarshalAs(UnmanagedType.LPWStr)] out string wszTrigger);
    };
    static public Guid CLSID_ITask      = new Guid("148BD520-A2AB-11CE-B11F-00AA00530503");
    static public Guid IID_ITask        = new Guid("148BD524-A2AB-11CE-B11F-00AA00530503");
    static public Guid IID_IPersistFile     = new Guid("0000010b-0000-0000-C000-000000000046");

    public enum TASK_TRIGGER_TYPE
    {
    TASK_TIME_TRIGGER_ONCE        = 0, // Ignore the Type field.
    TASK_TIME_TRIGGER_DAILY       = 1, // Use DAILY
    TASK_TIME_TRIGGER_WEEKLY      = 2, // Use WEEKLY
    TASK_TIME_TRIGGER_MONTHLYDATE     = 3, // Use MONTHLYDATE
    TASK_TIME_TRIGGER_MONTHLYDOW      = 4, // Use MONTHLYDOW
    TASK_EVENT_TRIGGER_ON_IDLE    = 5, // Ignore the Type field.
    TASK_EVENT_TRIGGER_AT_SYSTEMSTART = 6, // Ignore the Type field.
    TASK_EVENT_TRIGGER_AT_LOGON       = 7, // Ignore the Type field.
    }

    [Flags]
    public enum TASK_TRIGGER_FLAG
    [Guid("148BD524-A2AB-11CE-B11F-00AA00530503"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    interface ITask : IScheduledWorkItem
    {
    TASK_TRIGGER_FLAG_HAS_END_DATE     = 0x1,
    TASK_TRIGGER_FLAG_KILL_AT_DURATION_END = 0x2,
    TASK_TRIGGER_FLAG_DISABLED         = 0x4,
    }
    // Inherited from IScheduledWorkItem
    new int CreateTrigger(                      out ushort  iTrigger,
                [MarshalAs(UnmanagedType.IUnknown)] out object  trigger);
    new int DeleteTrigger(                      ushort      iTrigger);
    new int GetTriggerCount(                    out ushort  iTriggerCount);
    new int GetTrigger(                     ushort      iTrigger,
                [MarshalAs(UnmanagedType.IUnknown)] out object  trigger);

    [StructLayout(LayoutKind.Sequential)]
    public struct DAILY
    {
    public ushort DaysInterval;
    }
    new int GetTriggerString(                   ushort      iTrigger,
                [MarshalAs(UnmanagedType.LPWStr)]   out string  trigger);

    new int GetRunTimes(                    ref SYSTEMTIME pstBegin,
                                    ref SYSTEMTIME pstEnd,
                                    out ushort     count,
                                    out SYSTEMTIME rgstTaskTimes);

    new int GetNextRunTime(                     ref SYSTEMTIME pstNextRun);
    new int SetIdleWait(                    ushort     wIdleMinutes,
                                    ushort     wDeadlineMinutes);
    new int GetIdleWait(                    out ushort     wIdleMinutes,
                                    out ushort     wDeadlineMinutes);
    new int Run();
    new int Terminate( );
    new int EditWorkItem(                       IntPtr     hParent,
                                    uint       dwReserved);
    new int GetMostRecentRunTime(                   out SYSTEMTIME pstLastRun);
    new int GetStatus(                      out uint       hrStatus);
    new int GetExitCode(                    out uint       dwExitCode);
    new int SetComment(       [MarshalAs(UnmanagedType.LPWStr)] string     Comment);
    new int GetComment(       [MarshalAs(UnmanagedType.LPWStr)] out string     Comment);
    new int SetCreator(       [MarshalAs(UnmanagedType.LPWStr)] string     Creator);
    new int GetCreator(       [MarshalAs(UnmanagedType.LPWStr)] out string     Creator);
    new int SetWorkItemData( ushort cbData,Byte[] rgbData);
    new int GetWorkItemData(  out ushort cbData,
                  out Byte[] rgbData);
    new int SetErrorRetryCount( ushort wRetryCount);
    new int GetErrorRetryCount( out ushort wRetryCount);
    new int SetErrorRetryInterval( ushort wRetryInterval);
    new int GetErrorRetryInterval( out ushort wRetryInterval);
    new int SetFlags( uint dwFlags);
    new int GetFlags( out uint dwFlags);
    new int SetAccountInformation(  [MarshalAs(UnmanagedType.LPWStr)] string AccountName,
                    [MarshalAs(UnmanagedType.LPWStr)] string PassUInt16);
    new int GetAccountInformation(  [MarshalAs(UnmanagedType.LPWStr)] out string AccountName);

    [StructLayout(LayoutKind.Sequential)]
    public struct WEEKLY
    {
    public ushort WeeksInterval;
    public ushort rgfDaysOfTheWeek;
    // Methods specific to ITask
    int SetApplicationName([MarshalAs(UnmanagedType.LPWStr)]   string ApplicationName);
    int GetApplicationName([MarshalAs(UnmanagedType.LPWStr)] out string ApplicationName);
    int SetParameters([MarshalAs(UnmanagedType.LPWStr)]   string Parameters);
    int GetParameters([MarshalAs(UnmanagedType.LPWStr)] out string Parameters);
    int SetWorkingDirectory([MarshalAs(UnmanagedType.LPWStr)]   string WorkingDirectory);
    int GetWorkingDirectory([MarshalAs(UnmanagedType.LPWStr)] out string WorkingDirectory);
    int SetPriority(uint Priority);
    int GetPriority(out uint Priority);
    int SetTaskFlags(uint Flags);
    int GetTaskFlags(out uint Flags);
    int SetMaxRunTime(uint MaxRunTimeMS);
    int GetMaxRunTime(out uint MaxRunTimeMS);
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct MONTHLYDATE
    public struct SYSTEMTIME
    {
    public uint rgfDays;
    public ushort rgfMonths;
    [MarshalAs(UnmanagedType.U2)] short Year;
    [MarshalAs(UnmanagedType.U2)] short Month;
    [MarshalAs(UnmanagedType.U2)] short DayOfWeek;
    [MarshalAs(UnmanagedType.U2)] short Day;
    [MarshalAs(UnmanagedType.U2)] short Hour;
    [MarshalAs(UnmanagedType.U2)] short Minute;
    [MarshalAs(UnmanagedType.U2)] short Second;
    [MarshalAs(UnmanagedType.U2)] short Milliseconds;
    }

    [StructLayout(LayoutKind.Sequential)]
    public struct MONTHLYDOW
    {
    public ushort wWhichWeek;
    public ushort rgfDaysOfTheWeek;
    public ushort rgfMonths;
    }

C# Helper Code

    using System;
    using System.Runtime.InteropServices;

    [StructLayout(LayoutKind.Explicit)]
    public struct TRIGGER_TYPE_UNION
    static public int SaveTask(object task)
    {
    [FieldOffset(0)] public DAILY       Daily;
    [FieldOffset(0)] public WEEKLY      Weekly;
    [FieldOffset(0)] public MONTHLYDATE MonthlyDate;
    [FieldOffset(0)] public MONTHLYDOW  MonthlyDOW;
    }
    IntPtr  fileObj;
    int     hr = 0;

    [StructLayout(LayoutKind.Sequential)]
    public struct TASK_TRIGGER
    {
    public ushort          cbTriggerSize;
    public ushort          Reserved1;
    public ushort          wBeginYear;
    public ushort          wBeginMonth;
    public ushort          wBeginDay;
    public ushort          wEndYear;
    public ushort          wEndMonth;
    public ushort          wEndDay;
    public ushort          wStartHour;
    public ushort          wStartMinute;
    public uint        MinutesDuration;
    public uint        MinutesInterval;
    public TASK_TRIGGER_FLAG   rgFlags;
    public TASK_TRIGGER_TYPE   TriggerType;
    public TRIGGER_TYPE_UNION  Type;
    public ushort          Reserved2;
    public ushort          wRandomMinutesInterval;
    hr = Marshal.QueryInterface(Marshal.GetIUnknownForObject(task), ref IID_IPersistFile, out fileObj);
    if (hr != 0)
        return hr;

    static public TASK_TRIGGER CreateInstance()
    {
        TASK_TRIGGER obj = new TASK_TRIGGER();
        obj.cbTriggerSize = (ushort)Marshal.SizeOf(obj);
        return obj;
    }
    }
    IPersistFile file = Marshal.GetObjectForIUnknown(fileObj) as IPersistFile;

VB Definition:

<ComImport> _
<Guid("TODO")> _
'TODO: Insert <InterfaceType(ComInterfaceType.InterfaceIsIUnknown)> _ if this doesn't derive from IDispatch
Interface ITaskTrigger
TODO
End Interface

User-Defined Types:

None.

    file.Save(null, true);
    return hr;
    }

Notes:

VB Definition:

<ComImport> _
<Guid("TODO")> _
'TODO: Insert <InterfaceType(ComInterfaceType.InterfaceIsIUnknown)> _ if this doesn't derive from IDispatch
Interface ITask
TODO
End Interface