how to change desktop wallpaper?

How do I change desktop wallpaper?

I tried this

procedure TForm1.Button1Click(Sender: TObject); 
var   
  PicPath: String; 
begin 
  PicPath := 'C:\test.bmp';   
  SystemParametersInfo(SPI_SETDESKWALLPAPER, 0, pChar(PicPath), SPIF_SENDCHANGE) 
end;开发者_如何学C

But it didn't work.

I just tried it with D2007 on XP (and also D2009 on Vista), and this code works.
But to catch If and why it is not working, you should test the result code and get the error from Windows:

  if not SystemParametersInfo(SPI_SETDESKWALLPAPER, 0, pChar(PicPath), SPIF_SENDCHANGE)then
    RaiseLastOSError;

In most cases, it will be because the bmp file is not found:

System Error.  Code: 2.
The system cannot find the file specified.

You can check out this python script: http://gaze.svn.sourceforge.net/viewvc/gaze/trunk/implementation/src/gazelib/os_interface.py?view=markup

This is the python method that does all the magic. It changes a few registry keys and then calls a system method to update the wallpaper.

  103   def set_wallpaper(self, file_path) :
  104       self.__lock.acquire()
  105       # this module is part of python 2.5 by default
  106       import ctypes
  107       import _winreg
  108       reg = _winreg.OpenKey(_winreg.HKEY_CURRENT_USER, self.__REGISTRY_PATH, 0, _winreg.KEY_SET_VALUE)
  109       # First center the image and turn off tiling
  110       _winreg.SetValueEx(reg, "TileWallpaper", 0, _winreg.REG_SZ, "0")
  111       _winreg.SetValueEx(reg, "WallpaperStyle", 0, _winreg.REG_SZ, "0")
  112       # Set the image
  113       _winreg.SetValueEx(reg, "ConvertedWallpaper", 0, _winreg.REG_SZ, os.path.realpath(file_path))
  114       _winreg.SetValueEx(reg, "Wallpaper", 0, _winreg.REG_SZ, self.convert_to_bmp(file_path))
  115       _winreg.CloseKey(reg)
  116       # Notify the changes to the system
  117       func_ret_val = ctypes.windll.user32.SystemParametersInfoA(\
  118           self.__SPI_SETDESKWALLPAPER,\
  119           0,\
  120           None,\
  121           self.__SPIF_UPDATEINIFILE | self.__SPIF_SENDWININICHANGE)
  122       assert func_ret_val == 1
  123       self.__lock.release()

Check a VB code here, it can give you a clue.

SystemParametersInfo(SPI_SETDESKWALLPAPER, 0, imageLocation, SPIF_UPDATEINIFILE Or SPIF_SENDWININICHANGE)

This should work

Procedure TForm1.Button1Click(Sender: TObject);
var
  PicPath : string;
begin
  PicPath := 'C:\test.bmp';
  SystemParametersInfo(SPI_SETDESKWALLPAPER, 0, Pointer(PicPath), SPIF_SENDWININICHANGE);
end;