Description

Here's a little sample that provides you with a means to enumerate all the available monitors on a system. Do you, perhaps, need to cover the entire screen with a single form? No problem! Drop the two provided modules, MMonitors.bas and CMonitor.cls, into your project and then add code something like this:

Private Sub cmdCoverScreen_Click()
   ' Need to refresh collection at least once.
   Call MonitorsRefresh
   With Monitors("0")
      .PixelsToTwips = True
      Me.Move .Left, .Top, .Width, .Height
   End With
End Sub

The Monitors collection is keyed using the same values Windows uses to describe each monitor in the Display Properties dialog Settings tab. The astute among you will now be asking about Monitor Zero? That's a special one I added to the collection that represents the entire virtual desktop, so it therefore enables the call above to cover the entire screen.

Windows will also provide information about pseudo display devices, which are generally invisible and are often not part of the desktop. These critters are used by applications like Net Meeting to provide a display-like surface, and can generally be ignored for most application purposes. Nonetheless, you will find those at Key values higher than the number of actual physical monitors present on the system, and identifiable through the Visible and/or AttachedToDesktop properties of the CMonitor class.

I recently added some new functions that will facilitate repositioning a window where it was when the application was last shutdown. They go the extra mile of validating the coordinates, to be sure the user hasn't resized the display or changed the number of active monitors, and sliding an offscreen window back into visible space if desired. Also provided a very simple means of moving a window to the monitor where the mouse is, which may be a nice touch at application startup time?

   ' Make sure form first appears on the monitor that
   ' the mouse is over.
   Call WindowSwitchMonitor(Me.hWnd, MonitorFromMouse())

CMonitor Properties

Handle	The hMonitor value returned by EnumDisplayMonitors, MonitorFromPoint, MonitorFromRect, or MonitorFromWindow.
Index	Long value that matches the Key used when building collection as well as how Windows identifies this monitor.
PixelsToTwips	Boolean value that sets whether or not Pixel values are returned as Twips instead.
AttachedToDesktop	Read only: Boolean value that indicates whether this display is part of the desktop.
Device	Read only: String that represents the device name.
DeviceKey	Read only: String that represents the device key.
DeviceString	Read only: String that represents the device string.
DiminishedWorkspace	Read only: Workspace is reduced by taskbar(s) to size smaller than monitor.
MultiMonitorSupport	Read only: Boolean that indicates operating system support for multiple monitors.
Primary	Read only: Boolean that indicates whether or not this is the primary monitor.
Removable	Read only: Indicates whether the device is removeable.
VgaCompatible	Read only: Indicates whether the device is VBA compatible.
Visible	Read only: Interprets whether the device is visible based on the inverse of the DISPLAY_DEVICE_MIRRORING_DRIVER flag.
Bottom, WorkBottom	Read only: Bottom coordinate for the display or work area.
Height, WorkHeight	Read only: Height of the display or work area.
Left, WorkLeft	Read only: Left coordinate for the display or work area.
Right, WorkRight	Read only: Right coordinate for the display or work area.
Top, WorkTop	Read only: Top coordinate for the display or work area.
Width, WorkWidth	Read only: Width of the display or work area.

CMonitor Methods

Refresh

Refreshes all cached information about this particular display device.

MMonitor Methods

MonitorCount	Returns the number of physical monitors on the system.
MonitorSupport	Indicates operating system support for multiple monitors. Effectively whether this system is Windows 98/2000 or better.
MonitorFromMouse	Returns the number of the monitor that's under the mouse cursor.
MonitorFromPoint	Returns the number of the monitor that's under the point (logical pixels) specified.
MonitorFromRect	Returns the number of the monitor that the majority of the passed rectangle falls upon.
MonitorFromWindow	Returns the number of the monitor that the majority of the passed window falls upon.
MonitorRect	Returns a RECT structure that represents the display coordinates of the specified monitor number.
MonitorWorkRect	Returns a RECT structure that represents the work area coordinates of the specified monitor number.
MonitorsRefresh	Refreshes the global Monitors collection. Must be called at least once per application before accessing the collection directly.
FormatRect	Returns cartesian coordinate display of rectangle coordinates. eg, "(0,0)-(1024,768)"
WindowMove	Simple wrapper that accepts a RECT rather than individual coordinates around MoveWindow API.
WindowOffscreen	Tests whether a window is wholly or partially offscreen, and optionally slides it back to nearest onscreen position if so.
WindowSwitchMonitor	Moves a window from one monitor to the exact same coordinates on another monitor.
WindowRectAbsolute	Simple wrapper around GetWindowRect API, which returns absolute window coordinates.
WindowRectRelative	Returns coordinates of window relative to the monitor it principally occupies.

Published

This sample, or the one from which it originally derived, was published (or at least peripherally mentioned) in the following article(s):

• Working with Multiple Monitors, Classic VB Corner, VSM Online, March 2009
• Thoughtful UI Tweaks Can Make All the Difference, Classic VB Corner, VSM Online, August 2009

APIs Usage

This sample uses the following API calls:

Module	Library	Function
CMonitor.cls	kernel32 user32	GetVersionEx RtlZeroMemory EnumDisplayDevices EqualRect GetMonitorInfo GetSystemMetrics SystemParametersInfo
CStringBuilder.cls	kernel32 msvbvm60	RtlMoveMemory VarPtr
MMonitors.bas	user32	EnumDisplayMonitors EqualRect GetCursorPos GetSystemMetrics GetWindowRect IntersectRect MonitorFromPoint MonitorFromRect MonitorFromWindow MoveWindow OffsetRect UnionRect

Don't see what you're looking for? Here's a complete API cross-reference.

Download

Please, enjoy and learn from this sample. Include its code within your own projects, if you wish. But, in order to insure only the most recent code is available to all, I ask that you don't share the sample by any form of mass distribution. Download Monitors.zip, 27Kb, Last Updated: Friday, 7 August 2009

See Also

The following resources may also be of interest:

• SnapDialog - Snap dialogs to the edges of screen. Supports multiple monitors and taskbar avoidance. Uses native subclassing.