C# 获取windows系统的显示器个数

缘由

最近有个工装的项目，测试HDMI接口可不可用，采取了诱骗器的方式，软件需要读到当前是否有外接屏幕的插入，最简单的就是来获取屏幕的数量，从而判断是否有外接屏幕的介入。因此有了需要查询Windows系统显示器个数的需求。

尝试过的方法

方法1

Screen.AllScreens.Count();

这个方法是利用WinForm中的Screen类，从而获得当前屏幕的数量。

方法2

using System.Management;

int number = 0;
ManagementObjectSearcher searcher = new ManagementObjectSearcher("root\\CIMV2", "SELECT * FROM Win32_DesktopMonitor");
foreach (ManagementObject queryObj in searcher.Get())
{
	number++;
}

这个方法是利用WMI来查询当前系统中的显示器，得到显示信息的列表，循环得到列表的个数，从而得到显示器的个数。

方法3

[StructLayout(LayoutKind.Sequential)]
public struct Rect
{
    public int left;
    public int top;
    public int right;
    public int bottom;
}

[DllImport("user32.dll")]
static extern bool EnumDisplayMonitors(IntPtr hdc, IntPtr lprcClip,
   EnumMonitorsDelegate lpfnEnum, IntPtr dwData);

private delegate bool MonitorEnumProc(IntPtr hDesktop, IntPtr hdc, ref ScreenRect pRect, int dwData);

int monCount = 0;

MonitorEnumProc callback = (IntPtr hDesktop, IntPtr hdc, ref ScreenRect prect, int d) => ++monCount > 0;

if (!EnumDisplayMonitors(IntPtr.Zero, IntPtr.Zero, callback, 0))
	Console.WriteLine("An error occured while enumerating monitors");
return monCount;

这个方法是利用Win32中的EnumDisplayMonitors方法来枚举当前系统中存在的显示器，通过回调来进行一个显示器个数的计算。

方法4

[Flags()]
public enum DisplayDeviceStateFlags : int
{
    /// <summary>The device is part of the desktop.</summary>
    AttachedToDesktop = 0x1,
    MultiDriver = 0x2,
    /// <summary>The device is part of the desktop.</summary>
    PrimaryDevice = 0x4,
    /// <summary>Represents a pseudo device used to mirror application drawing for remoting or other purposes.</summary>
    MirroringDriver = 0x8,
    /// <summary>The device is VGA compatible.</summary>
    VGACompatible = 0x10,
    /// <summary>The device is removable; it cannot be the primary display.</summary>
    Removable = 0x20,
    /// <summary>The device has more display modes than its output devices support.</summary>
    ModesPruned = 0x8000000,
    Remote = 0x4000000,
    Disconnect = 0x2000000
}
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct DISPLAY_DEVICE
{
    [MarshalAs(UnmanagedType.U4)]
    public int cb;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 32)]
    public string DeviceName;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 128)]
    public string DeviceString;
    [MarshalAs(UnmanagedType.U4)]
    public DisplayDeviceStateFlags StateFlags;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 128)]
    public string DeviceID;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 128)]
    public string DeviceKey;
}
[DllImport("user32.dll")]
static extern bool EnumDisplayDevices(string lpDevice, uint iDevNum, ref DISPLAY_DEVICE lpDisplayDevice, uint dwFlags);

public void Display()
{
    DISPLAY_DEVICE d = new DISPLAY_DEVICE();
    d.cb = Marshal.SizeOf(d);
    int number=0;
    try
    {
        for (uint id = 0; EnumDisplayDevices(null, id, ref d, 0); id++)
        {
            if (d.StateFlags.HasFlag(DisplayDeviceStateFlags.AttachedToDesktop))
            {
                //计算个数
                number++;
                //输出相关信息
                Console.WriteLine(
                    String.Format("{0}, {1}, {2}, {3}, {4}, {5}",
                             id,
                             d.DeviceName,
                             d.DeviceString,
                             d.StateFlags,
                             d.DeviceID,
                             d.DeviceKey
                             )
                             );
                d.cb = Marshal.SizeOf(d);
                EnumDisplayDevices(d.DeviceName, 0, ref d, 0);
                Console.WriteLine(String.Format("{0}, {1}",
                             d.DeviceName,
                             d.DeviceString
                             )
                             );
            }
            d.cb = Marshal.SizeOf(d);
        }
    }
    catch (Exception ex)
    {
        Console.WriteLine(String.Format("{0}", ex.ToString()));
    }
}

这个方法是利用Win32中的EnumDisplayDevices方法来枚举当前系统中存在的显示器，通过循环来进行一个显示器个数的计算。

方法5

public enum SystemMetric
{
	//其他类型查看：https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-getsystemmetrics
	SM_CMONITORS=80,
	...
}

[DllImport("user32.dll")]
static extern int GetSystemMetrics(SystemMetric smIndex);

int screenNum=GetSystemMetrics(SystemMetric.SM_CMONITORS);

这个方法是利用Win32中的GetSystemMetrics方法来获取当前系统中存在的显示器个数，这个方法还可以查询系统的其他信息，详情参照官方文档。

重点来了:如果接两个显示器，设置系统处于复制模式（Clone/duplicate），则上述方法都失效，只能找到一个显示设备，但是项目正好是这个模式，哎

接下来咱们来一个不受模式影响的方法X

原理：每个种类的设备在系统中有一个类Guid，我们可以通过设备管理器中设备的属性中查看，如下图。然后我们用Win32的API枚举设备管理器中的设备，然后通过类Guid对设备进行筛选，从而筛选出屏幕设备，然后计算个数。

[Flags]
public enum DIGCF : uint
{
    DEFAULT = 0x00000001,
    PRESENT = 0x00000002,
    ALLCLASSES = 0x00000004,
    PROFILE = 0x00000008,
    DEVICEINTERFACE = 0x00000010
}

[StructLayout(LayoutKind.Sequential)]
public struct SP_DEVINFO_DATA
{
    public UInt32 cbSize;
    public Guid ClassGuid;
    public UInt32 DevInst;
    public IntPtr Reserved;
}

[StructLayout(LayoutKind.Sequential)]
public struct SP_DEVINFO_DATA
{
    public UInt32 cbSize;
    public Guid ClassGuid;
    public UInt32 DevInst;
    public IntPtr Reserved;
}

[DllImport("setupapi.dll", SetLastError = true)]
public static extern bool SetupDiDestroyDeviceInfoList(IntPtr handle);

[DllImport("setupapi.dll", SetLastError = true)]
public static extern IntPtr SetupDiGetClassDevsW([In] ref Guid ClassGuid, [MarshalAs(UnmanagedType.LPWStr)]string Enumerator, IntPtr parent, DIGCF flags);

[DllImport("setupapi.dll", SetLastError = true)]
public static extern bool SetupDiEnumDeviceInfo(IntPtr deviceInfoSet, UInt32 memberIndex, [Out] out SP_DEVINFO_DATA deviceInfoData);

int screenNum=0;
Guid NullGuid = Guid.Empty;
IntPtr info = SetupDiGetClassDevsW(ref NullGuid, null, IntPtr.Zero, DIGCF.ALLCLASSES|DIGCF.PROFILE);
SP_DEVINFO_DATA devdata = new SP_DEVINFO_DATA();
devdata.cbSize = (UInt32)Marshal.SizeOf(devdata);
//遍历设备
for (uint i = 0; SetupDiEnumDeviceInfo(info, i, out devdata); i++)
{
    if (devdata.ClassGuid == new Guid("{4d36e96e-e325-11ce-bfc1-08002be10318}"))
    {
        screenNum++;
    }
}
if (info != IntPtr.Zero)
SetupDiDestroyDeviceInfoList(info);

总结

最后这个方法只要是设备管理器中可以看见的设备均可以查询到，拿到更加原始的数据，不过相对的查询速度会慢一些，不过解决了问题，值得庆祝，分享给大家，希望大家少走弯路。

踩坑的道路永不停歇！