win7自动壁纸切换小工具AutoDesk二：fade effect的壁纸切换

要实现壁纸切换，可以用函数WinAPI.SystemParametersInfo(20, 1, strSavePath, 1)来实现。

strSavePath为图片的位置，实际测下来该函数并不要求图片一定是bmp格式，jpg|png也都可以的。

函数的原型声明如下：

class WinAPI
    {
        
        [DllImport("user32.dll", CharSet=CharSet.Auto)]
        public static  extern int SystemParametersInfo (int uAction , int uParam , string lpvParam , int fuWinIni);
    }

该函数的问题就是没有fade效果，只直接换壁纸，非常的突兀。要实现fade效果需要活动桌面，即接口IActiveDesktop.

msdn的介绍说是：

Allows a client program to manage the desktop items and wallpaper on a local computer。

设计到COM编程。下面是IActiveDesktop的c#的实现。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;

namespace AutoDesk
{
        public struct WALLPAPEROPT
        {
            public static readonly int SizeOf = Marshal.SizeOf(typeof(WALLPAPEROPT));
        }

        public enum WallPaperStyle : int
        {
            WPSTYLE_CENTER = 0,
            WPSTYLE_TILE = 1,
            WPSTYLE_STRETCH = 2,
            WPSTYLE_MAX = 3
        }

        [Flags]
        public enum AD_Apply : int
        {
            SAVE = 0x00000001,
            HTMLGEN = 0x00000002,
            REFRESH = 0x00000004,
            ALL = SAVE | HTMLGEN | REFRESH,
            FORCE = 0x00000008,
            BUFFERED_REFRESH = 0x00000010,
            DYNAMICREFRESH = 0x00000020
        }

        [StructLayout(LayoutKind.Sequential)]
        public struct COMPONENTSOPT
        {
            public static readonly int SizeOf = Marshal.SizeOf(typeof(COMPONENTSOPT));
            public int dwSize;
            [MarshalAs(UnmanagedType.Bool)]
            public bool fEnableComponents;
            [MarshalAs(UnmanagedType.Bool)]
            public bool fActiveDesktop;
        }

        [Flags]
        public enum CompItemState : int
        {
            NORMAL = 0x00000001,
            FULLSCREEN = 00000002,
            SPLIT = 0x00000004,
            VALIDSIZESTATEBITS = NORMAL | SPLIT | FULLSCREEN,
            VALIDSTATEBITS = NORMAL | SPLIT | FULLSCREEN | unchecked((int)0x80000000) | 0x40000000
        }

        [StructLayout(LayoutKind.Sequential)]
        public struct COMPSTATEINFO
        {
            public static readonly int SizeOf = Marshal.SizeOf(typeof(COMPSTATEINFO));
            public int dwSize;
            public int iLeft;
            public int iTop;
            public int dwWidth;
            public int dwHeight;
            public CompItemState dwItemState;
        }

        [StructLayout(LayoutKind.Sequential)]
        public struct COMPPOS
        {
            public const int COMPONENT_TOP = 0x3FFFFFFF;
            public const int COMPONENT_DEFAULT_LEFT = 0xFFFF;
            public const int COMPONENT_DEFAULT_TOP = 0xFFFF;
            public static readonly int SizeOf = Marshal.SizeOf(typeof(COMPPOS));

            public int dwSize;
            public int iLeft;
            public int iTop;
            public int dwWidth;
            public int dwHeight;
            public int izIndex;
            [MarshalAs(UnmanagedType.Bool)]
            public bool fCanResize;
            [MarshalAs(UnmanagedType.Bool)]
            public bool fCanResizeX;
            [MarshalAs(UnmanagedType.Bool)]
            public bool fCanResizeY;
            public int iPreferredLeftPercent;
            public int iPreferredTopPercent;
        }

        public enum CompType : int
        {
            HTMLDOC = 0,
            PICTURE = 1,
            WEBSITE = 2,
            CONTROL = 3,
            CFHTML = 4
        }

        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode, Pack = 8)]
        public struct COMPONENT
        {
            private const int INTERNET_MAX_URL_LENGTH = 2084; // = INTERNET_MAX_SCHEME_LENGTH (32) + "://\0".Length +   INTERNET_MAX_PATH_LENGTH (2048)
            public static readonly int SizeOf = Marshal.SizeOf(typeof(COMPONENT));

            public int dwSize;
            public int dwID;
            public CompType iComponentType;
            [MarshalAs(UnmanagedType.Bool)]
            public bool fChecked;
            [MarshalAs(UnmanagedType.Bool)]
            public bool fDirty;
            [MarshalAs(UnmanagedType.Bool)]
            public bool fNoScroll;
            public COMPPOS cpPos;
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 260)]
            public string wszFriendlyName;
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = INTERNET_MAX_URL_LENGTH)]
            public string wszSource;
            [MarshalAs(UnmanagedType.ByValTStr, SizeConst = INTERNET_MAX_URL_LENGTH)]
            public string wszSubscribedURL;

            public int dwCurItemState;
            public COMPSTATEINFO csiOriginal;
            public COMPSTATEINFO csiRestored;
        }

        public enum DtiAddUI : int
        {
            DEFAULT = 0x00000000,
            DISPSUBWIZARD = 0x00000001,
            POSITIONITEM = 0x00000002,
        }

        [Flags]
        public enum ComponentModify : int
        {
            TYPE = 0x00000001,
            CHECKED = 0x00000002,
            DIRTY = 0x00000004,
            NOSCROLL = 0x00000008,
            POS_LEFT = 0x00000010,
            POS_TOP = 0x00000020,
            SIZE_WIDTH = 0x00000040,
            SIZE_HEIGHT = 0x00000080,
            POS_ZINDEX = 0x00000100,
            SOURCE = 0x00000200,
            FRIENDLYNAME = 0x00000400,
            SUBSCRIBEDURL = 0x00000800,
            ORIGINAL_CSI = 0x00001000,
            RESTORED_CSI = 0x00002000,
            CURITEMSTATE = 0x00004000,
            ALL = TYPE | CHECKED | DIRTY | NOSCROLL | POS_LEFT | SIZE_WIDTH |
                SIZE_HEIGHT | POS_ZINDEX | SOURCE |
                FRIENDLYNAME | POS_TOP | SUBSCRIBEDURL | ORIGINAL_CSI |
                RESTORED_CSI | CURITEMSTATE
        }

        [Flags]
        public enum AddURL : int
        {
            SILENT = 0x0001
        }

        [ComImport]
        [Guid("F490EB00-1240-11D1-9888-006097DEACF9")]
        [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
        public interface IActiveDesktop
        {
            [PreserveSig]
            int ApplyChanges(AD_Apply dwFlags);
            [PreserveSig]
            int GetWallpaper([MarshalAs(UnmanagedType.LPWStr)]  System.Text.StringBuilder pwszWallpaper,
                int cchWallpaper,
                int dwReserved);
            [PreserveSig]
            int SetWallpaper([MarshalAs(UnmanagedType.LPWStr)] string pwszWallpaper, int dwReserved);
            [PreserveSig]
            int GetWallpaperOptions(ref WALLPAPEROPT pwpo, int dwReserved);
            [PreserveSig]
            int SetWallpaperOptions(ref WALLPAPEROPT pwpo, int dwReserved);
            [PreserveSig]
            int GetPattern([MarshalAs(UnmanagedType.LPWStr)] System.Text.StringBuilder pwszPattern, int cchPattern, int dwReserved);
            [PreserveSig]
            int SetPattern([MarshalAs(UnmanagedType.LPWStr)] string pwszPattern, int dwReserved);
            [PreserveSig]
            int GetDesktopItemOptions(ref COMPONENTSOPT pco, int dwReserved);
            [PreserveSig]
            int SetDesktopItemOptions(ref COMPONENTSOPT pco, int dwReserved);
            [PreserveSig]
            int AddDesktopItem(ref COMPONENT pcomp, int dwReserved);
            [PreserveSig]
            int AddDesktopItemWithUI(IntPtr hwnd, ref COMPONENT pcomp, DtiAddUI dwFlags);
            [PreserveSig]
            int ModifyDesktopItem(ref COMPONENT pcomp, ComponentModify dwFlags);
            [PreserveSig]
            int RemoveDesktopItem(ref COMPONENT pcomp, int dwReserved);
            [PreserveSig]
            int GetDesktopItemCount(out int lpiCount, int dwReserved);
            [PreserveSig]
            int GetDesktopItem(int nComponent, ref COMPONENT pcomp, int dwReserved);
            [PreserveSig]
            int GetDesktopItemByID(IntPtr dwID, ref COMPONENT pcomp, int dwReserved);
            [PreserveSig]
            int GenerateDesktopItemHtml([MarshalAs(UnmanagedType.LPWStr)] string pwszFileName, ref COMPONENT pcomp, int dwReserved);
            [PreserveSig]
            int AddUrl(IntPtr hwnd, [MarshalAs(UnmanagedType.LPWStr)] string pszSource, ref COMPONENT pcomp, AddURL dwFlags);
            [PreserveSig]
            int GetDesktopItemBySource([MarshalAs(UnmanagedType.LPWStr)] string pwszSource, ref COMPONENT pcomp, int dwReserved);

        }

        /// <summary>
        /// Summary description for shlobj.
        /// Written by: Eber Irigoyen
        /// on: 11/23/2005
        /// </summary>
        public class shlobj
        {
            public static readonly Guid CLSID_ActiveDesktop =
                new Guid("{75048700-EF1F-11D0-9888-006097DEACF9}");

            public static IActiveDesktop GetActiveDesktop()
            {
                Type typeActiveDesktop = Type.GetTypeFromCLSID(shlobj.CLSID_ActiveDesktop);
                return (IActiveDesktop)Activator.CreateInstance(typeActiveDesktop);
            }

            public shlobj()
            {
                //
                // TODO: Add constructor logic here
                //
            }
        }
    
}

其使用方法如前面的函数

private void switch_to_next_waller()
        {
            string strSavePath = Path.Combine(m_deskpick_path, get_random_pick_name());
            //WinAPI.SystemParametersInfo(20, 1, strSavePath, 1);
            IActiveDesktop iad = shlobj.GetActiveDesktop();
            iad.SetWallpaper(strSavePath, 0);
            iad.ApplyChanges(AD_Apply.ALL | AD_Apply.FORCE | AD_Apply.BUFFERED_REFRESH);
            System.Runtime.InteropServices.Marshal.ReleaseComObject(iad);
        }

只需要调用SetWallpaper函数，然后释放该COMObject就可以实现fade效果的切换壁纸。

调用该函数的实际效果是，在win7的主题中有一个未保存的主题，该主题总是包含你切换的最后一张图片。

附上项目文件，供有兴趣的同学参考

https://files.cnblogs.com/linbirg/AutoDesk.rar