Bummer. Well, I was hoping.
We can't help you unless you post your code.
Ok. Bear in mind, the interesting parts of this (the dll import line, the
SystemParametersInfo() call, the registry key business) are what I got
from that sample on CodeProject. I altered that code to take an ordinary
filesystem path as input (rather than a URI), and to add a "Zoomed"
display mode which scales an image file up/down to fit the desktop while
maintaining the original aspect ratio (that is, what you always wanted the
"stretched" mode to do, but doesn't).
The rest of my application calls Wallpaper.Set() at various times to
attempt to change the wallpaper. When I step through the code, everything
happens exactly like I expect it to (i.e. temp file gets created if
necessary, correct path gets passed to SystemParametersInfo, etc.), but
after the call to SystemParametersInfo(), the desktop image has not been
changed. It has, however, been un-set from its previous value in such a
way that when windows needs to re-paint portions of the desktop, it
repaints them with the solid desktop color rather than with image data.
=============
using System;
using System.Drawing;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using System.IO;
using System.Data;
using Microsoft.Win32;
namespace DesktopSlideshow
{
/// <summary>
/// Class that encapsulates the functionality of putting an image file
onto the desktop.
/// </summary>
public sealed class Wallpaper
{
Wallpaper( ) { }
const int SPI_SETDESKWALLPAPER = 20;
const int SPIF_UPDATEINIFILE = 0x01;
const int SPIF_SENDWININICHANGE = 0x02;
[DllImport("user32.dll", CharSet=CharSet.Auto)]
static extern int SystemParametersInfo (int uAction, int uParam, string
lpvParam, int fuWinIni);
public enum Style : int
{
Tiled,
Centered,
Stretched,
Zoomed
}
public static void Set ( string path, Style style )
{
// get registry key for the desktop image settings
RegistryKey key = Registry.CurrentUser.OpenSubKey( @"Control
Panel\Desktop", true ) ;
// Zoomed is not supported natively, so we create a new image file
that is sized to work
// with Centered instead:
if(style == Style.Zoomed)
{
Size DS = SystemInformation.PrimaryMonitorSize;
Point DestPoint;
Size DestSize;
using(Bitmap B = new Bitmap(path)) // temporarily load the
image
using(Bitmap tmp = new Bitmap(DS.Width, DS.Height)) // new
bitmap as big as the desktop
{
double ratio = Math.Min((double)DS.Width /
(double)B.Width,
(double)DS.Height / (double)B.Height);
// Only do the resizing if the image would need to
scale more than 1%. Otherwise,
// just use the file as is.
if(Math.Abs(ratio - 1.0) > 0.01)
{
DestSize = new Size((int)(ratio * (double)B.Width),
(int)(ratio * (double)B.Height));
DestPoint = new Point(Math.Max(0, (DS.Width -
DestSize.Width)/2),
Math.Max(0, (DS.Height - DestSize.Height)/2));
// create the bitmap:
using (Graphics G = Graphics.FromImage(tmp))
{
G.DrawImage(B, new Rectangle(DestPoint.X,
DestPoint.Y, // resize the input image into tmp.
DestSize.Width, DestSize.Height));
}
// save it:
string tempPath = Path.Combine(Path.GetTempPath(),
"wallpaper.png");
tmp.Save(tempPath,
System.Drawing.Imaging.ImageFormat.Png);
// remember where we put it:
path = tempPath;
}
}
// default back to the Centered style.
style = Style.Centered;
}
if ( style == Style.Stretched )
{
key.SetValue(@"WallpaperStyle", 2.ToString( ) ) ;
key.SetValue(@"TileWallpaper", 0.ToString( ) ) ;
}
if ( style == Style.Centered )
{
key.SetValue(@"WallpaperStyle", 1.ToString( ) ) ;
key.SetValue(@"TileWallpaper", 0.ToString( ) ) ;
}
if ( style == Style.Tiled )
{
key.SetValue(@"WallpaperStyle", 1.ToString( ) ) ;
key.SetValue(@"TileWallpaper", 1.ToString( ) ) ;
}
SystemParametersInfo( SPI_SETDESKWALLPAPER,
0,
path,
SPIF_UPDATEINIFILE | SPIF_SENDWININICHANGE );
}
}
}
=============
