C# Signature:

[DllImport("user32.dll")]
static extern DISP_CHANGE ChangeDisplaySettingsEx(string lpszDeviceName, ref DEVMODE lpDevMode, IntPtr hwnd, ChangeDisplaySettingsFlags dwflags, IntPtr lParam);
static extern DISP_CHANGE ChangeDisplaySettingsEx(string lpszDeviceName, ref DEVMODE lpDevMode, IntPtr hwnd, uint dwflags, IntPtr lParam);

VB.NET

<DllImport("user32.dll")> _
Private Shared Function ChangeDisplaySettingsEx(ByVal lpszDeviceName As String, ByRef lpDevMode As DEVMODE, ByVal hwnd As IntPtr, ByVal dwflags As UInteger, ByVal lParam As IntPtr) As DISP_CHANGE
End Function

User-Defined Types:

DISP_CHANGE

DEVMODE

ChangeDisplaySettingsFlags

Notes:

See also ChangeDisplaySettings

Tips & Tricks:

To change the postion of a secondary device it is very important to use dmPositionX and dmPositionY from DEVMODE (see structs).

First i tried it with a PointL struct dmPosition.x and dmPosition.y until i luckily found this page:

http://msdn2.microsoft.com/en-us/library/aa719104(vs.71).aspx

Sample Code:

You can not enable and set size in one call. If the second monitor is not enabled you must first call ChangeDisplaySettingsEx with dmFields = DM.Position, with dmPosition set something other than (0,0). Once enabled you can call ChangeDisplaySettingsEx again with dmFields = DM.PelsHeight | DM.PelsWidth | DM.Position to set position and size. To disable the monitor call ChangeDisplaySettingsEx with dmFields=DM.Position, with dmPosition set to (0,0). Disabling will not work if dmFields = DM.PelsHeight | DM.PelsWidth | DM.Position.

DISPLAY_DEVICE d = new DISPLAY_DEVICE();
DEVMODE dm = new DEVMODE();
d.cb = Marshal.SizeOf(d);
int deviceID=1; // This is only for my device setting. Go through the whole EnumDisplayDevices to find your device  
EnumDisplayDevices(null,deviceID, ref  d, 0); //
EnumDisplaySettings(d.DeviceName, 0, ref dm);
dm.dmPelsWidth = 1024;
dm.dmPelsHeight = 768;
dm.dmPositionX = Screen.PrimaryScreen.Bounds.Right;
dm.dmFields = DM.Position | DM.PelsWidth | DM.PelsHeight;
ChangeDisplaySettingsEx(d.DeviceName, ref dm, IntPtr.Zero, CDS_UPDATEREGISTRY, IntPtr.Zero);

Alternative Managed API:

Do you know one? Please contribute it!

Sample Code:

DISPLAY_DEVICE d = new DISPLAY_DEVICE();
DEVMODE dm = new DEVMODE();
d.cb = Marshal.SizeOf(d);
int deviceID=1; // This is only for my device setting. Go through the whole EnumDisplayDevices to find your device  
EnumDisplayDevices(null,deviceID, ref  d, 0); //
EnumDisplaySettings(d.DeviceName, 0, ref dm);
dm.dmPelsWidth = 1024;
dm.dmPelsHeight = 768;
dm.dmPositionX = Screen.PrimaryScreen.Bounds.Right;
dm.dmFields = DM.Position | DM.PelsWidth | DM.PelsHeight;
ChangeDisplaySettingsEx(d.DeviceName, ref dm, IntPtr.Zero, CDS_UPDATEREGISTRY, IntPtr.Zero);

Alternative Managed API:

Do you know one? Please contribute it!

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