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Eu tentei alterar o fuso horário do meu sistema com código c # por alguns dias e nada do que estou tentando faz muito sentido ou funciona. Comecei tentando usar a sintaxe PInvoke para SetTimeZoneInformation que já vi em outras perguntas aqui.

[DllImport("kernel32.dll", CharSet = CharSet.Auto)] private static extern bool
SetTimeZoneInformation([In] ref TimeZoneInformation lpTimeZoneInformation);

Eu estava pensando em como eu deveria criar a estrutura TimeZoneInformation e fiquei confuso, pois meu sistema obviamente possui um sistema DST dinâmico. Acontece que, desde o Vista, a Microsoft adicionou uma nova maneira de lidar com os fusos horários. Agora você precisa usar SetDynamicTimeZoneInformation

[DllImport("kernel32.dll", CharSet = CharSet.Auto)]
private static extern bool SetDynamicTimeZoneInformation([In] ref DynamicTimeZoneInformation lpTimeZoneInformation);

Procurei ajuda com esta API no msdn e encontrei algo dizendo: "Um aplicativo deve ter o privilégio SE_TIME_ZONE_NAME para que essa função seja bem-sucedida". Eventualmente eu encontreiesta página com o que parece ser um bom código para fazer isso. O problema é que simplesmente não está funcionando.

Aqui está o meu código não útil:

[StructLayout(LayoutKind.Sequential)]
public struct LUID
{
    public int LowPart;
    public int HighPart;
}

[StructLayout(LayoutKind.Sequential)]
public struct TOKEN_PRIVILEGES
{
    public LUID Luid;
    public UInt32 Attributes;
    public UInt32 PrivilegeCount;
}

[StructLayoutAttribute(LayoutKind.Sequential)]
public struct SystemTime
{
    public ushort Year;
    public ushort Month;
    public ushort DayOfWeek;
    public ushort Day;
    public ushort Hour;
    public ushort Minute;
    public ushort Second;
    public ushort Millisecond;
}

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
public struct DynamicTimeZoneInformation
{
    public int bias;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)]
    public string standardName;
    public SystemTime standardDate;
    public int standardBias;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)]
    public string daylightName;
    public SystemTime daylightDate;
    public int daylightBias;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 128)]
    public string timeZoneKeyName;
    public bool dynamicDaylightTimeDisabled;
}

[DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
private static extern int GetDynamicTimeZoneInformation(out DynamicTimeZoneInformation lpTimeZoneInformation);

[DllImport("kernel32.dll", CharSet = CharSet.Auto)]
private static extern bool SetDynamicTimeZoneInformation([In] ref DynamicTimeZoneInformation lpTimeZoneInformation);

[DllImport("advapi32.dll", CharSet = CharSet.Auto, SetLastError = true)]
public static extern int OpenProcessToken(int ProcessHandle, int DesiredAccess, ref int tokenhandle);

[DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
public static extern int GetCurrentProcess();

[DllImport("advapi32.dll", CharSet = CharSet.Auto, SetLastError = true)]
public static extern int LookupPrivilegeValue(string lpsystemname, string lpname, [MarshalAs(UnmanagedType.Struct)] ref LUID lpLuid);

[DllImport("advapi32.dll", CharSet = CharSet.Auto, SetLastError = true)]
public static extern int AdjustTokenPrivileges(int tokenhandle, int disableprivs, [MarshalAs(UnmanagedType.Struct)]ref TOKEN_PRIVILEGES Newstate, int bufferlength, int PreivousState, int Returnlength);

public const int TOKEN_ASSIGN_PRIMARY = 0x00000001;
public const int TOKEN_DUPLICATE = 0x00000002;
public const int TOKEN_IMPERSONATE = 0x00000004;
public const int TOKEN_QUERY = 0x00000008;
public const int TOKEN_QUERY_SOURCE = 0x00000010;
public const int TOKEN_ADJUST_PRIVILEGES = 0x00000020;
public const int TOKEN_ADJUST_GROUPS = 0x00000040;
public const int TOKEN_ADJUST_DEFAULT = 0x00000080;

public const UInt32 SE_PRIVILEGE_ENABLED_BY_DEFAULT = 0x00000001;
public const UInt32 SE_PRIVILEGE_ENABLED = 0x00000002;
public const UInt32 SE_PRIVILEGE_REMOVED = 0x00000004;
public const UInt32 SE_PRIVILEGE_USED_FOR_ACCESS = 0x80000000;

public static bool EnablePrivilege(string privilege)
{
    try
    {
        int token = 0;
        int retVal = 0;

        TOKEN_PRIVILEGES TP = new TOKEN_PRIVILEGES();
        LUID LD = new LUID();

        retVal = OpenProcessToken(GetCurrentProcess(),
        TOKEN_ADJUST_PRIVILEGES | TOKEN_QUERY, ref token);
        retVal = LookupPrivilegeValue(null, privilege, ref LD);


        TP.PrivilegeCount = 1;
        TP.Attributes = SE_PRIVILEGE_ENABLED;
        TP.Luid = LD;

        retVal = AdjustTokenPrivileges(token, 0, ref TP, 1024, 0, 0);

        return true;
    }
    catch
    {
        return false;
    }
}

public static bool DisablePrivilege(string privilege)
{
    try
    {
        int token = 0;
        int retVal = 0;

        TOKEN_PRIVILEGES TP = new TOKEN_PRIVILEGES();
        LUID LD = new LUID();

        retVal = OpenProcessToken(GetCurrentProcess(), TOKEN_ADJUST_PRIVILEGES | TOKEN_QUERY, ref token);
        retVal = LookupPrivilegeValue(null, privilege, ref LD);
        TP.PrivilegeCount = 1;
        // TP.Attributes should be none (not set) to disable privilege
        TP.Luid = LD;

        retVal = AdjustTokenPrivileges(token, 0, ref TP, 1024, 0, 0);
        return true;
    }
    catch
    {
        return false;
    }
}

public bool SetSystemTimeZone(string timeZoneId)
{
    //I'm using the TimeZoneInfo class to populate a list in the UI.  This code to retrieve the correct timezone is working
    TimeZoneInfo newTimeZone = TimeZoneInfo.FindSystemTimeZoneById(timeZoneId);
    DynamicTimeZoneInformation dtzi = new DynamicTimeZoneInformation();
    dtzi.bias = -(Convert.ToInt32(newTimeZone.BaseUtcOffset.TotalMinutes));
    dtzi.standardBias = 0;
    //Here's where I start to lose it.  I don't know which adjustment rule to use from the GetAdjustmentRules call.  I'm just using the last one as that seems to usually be the most recent, but it doesn't always have to be.
    dtzi.daylightBias = Convert.ToInt32(newTimeZone.GetAdjustmentRules().Last().DaylightDelta.TotalMinutes);
    dtzi.standardName = newTimeZone.StandardName;
    dtzi.daylightName = newTimeZone.DaylightName;
    //It would be nice if this key name would just look up the timezone from the registry and use its settings
    dtzi.timeZoneKeyName = newTimeZone.Id;

    //No idea if this is the right way to create the SystemTime object I need here.
    SystemTime standardDate = new SystemTime();
    standardDate.Year = 0;
    standardDate.Hour = (ushort)newTimeZone.GetAdjustmentRules().Last().DaylightTransitionEnd.TimeOfDay.Hour;
    standardDate.Minute = (ushort)newTimeZone.GetAdjustmentRules().Last().DaylightTransitionEnd.TimeOfDay.Minute;
    standardDate.DayOfWeek = (ushort)newTimeZone.GetAdjustmentRules().Last().DaylightTransitionEnd.DayOfWeek;
    standardDate.Month = (ushort)newTimeZone.GetAdjustmentRules().Last().DaylightTransitionEnd.Month;
    standardDate.Day = (ushort)newTimeZone.GetAdjustmentRules().Last().DaylightTransitionEnd.Week;
    dtzi.standardDate = standardDate;

    SystemTime daylightDate = new SystemTime();
    standardDate.Year = 0;
    standardDate.Hour = (ushort)newTimeZone.GetAdjustmentRules().Last().DaylightTransitionStart.TimeOfDay.Hour;
    standardDate.Minute = (ushort)newTimeZone.GetAdjustmentRules().Last().DaylightTransitionStart.TimeOfDay.Minute;
    standardDate.DayOfWeek = (ushort)newTimeZone.GetAdjustmentRules().Last().DaylightTransitionStart.DayOfWeek;
    standardDate.Month = (ushort)newTimeZone.GetAdjustmentRules().Last().DaylightTransitionStart.Month;
    standardDate.Day = (ushort)newTimeZone.GetAdjustmentRules().Last().DaylightTransitionStart.Week;
    dtzi.daylightDate = daylightDate;

    dtzi.dynamicDaylightTimeDisabled = false;


    EnablePrivilege("SeTimeZonePrivilege");
    if (!SetDynamicTimeZoneInformation(ref dtzi))
        returnVal = false;
    DisablePrivilege("SeTimeZonePrivilege");

    return returnVal;
}

Alguém teve alguma sorte com isso ... definindo o fuso horário em um sistema pós-Vista? Talvez exista uma maneira melhor.

obrigado