问题
Using C# i'm trying to retrieve the name of the song that is currently playing and display it on a listBox, so every song that plays, it's shown in the listbox.
Using System;
Using WMPLib;
public IWMPMedia currentMedia { get; set; }
private void button1_Click(object sender, EventArgs e)
{
Player = new WMPLib.WindowsMediaPlayer();
string song = Player.currentMedia.name.ToString();
listBox1.Items.Add(song);
}
But it throws me the exception. "Object reference not set to an instance of an object" here:
string song = Player.currentMedia.name.ToString();
Does anyone knows how to solve this?
回答1:
You will have to use COM/OLE to do this. I did a program that did exactly that a little while ago, unfortunately tho I cannot find my client code, but I still have the code that implements IOleClientSite/IOleServiceProvider for WMPLib.
I found that code at the following URL: http://sirayuki.sakura.ne.jp/WmpSample/WmpRemote.zip
Its some code that was writen by Jonathan Dibble, a Microsoft employee if I remember correctly. There is a CHM in the Zip with some explanation on each of the classes.
Heres the code that I still have, in case the link goes down, but like I said I cannot find my code that uses it. It worked almost correctly but I remember that one of the bug left was that it would leave behind wmplayer.exe processes after the media player and my application were closed.
UPDATE!
found some client code and a slighlty modified version of RemotedWindowsMediaPlayer.cs
I just found some coded that I tested this with, and it works. Its from a Winform project, and you need to reference WMPLib for this to work.
In my form I added a button and this code:
/// <summary>
/// Default Constructor
/// </summary>
RemotedWindowsMediaPlayer rm;
public FrmMain()
{
//
// Required for Windows Form Designer support
//
InitializeComponent();
//Call me old fashioned - I like to do this stuff manually. You can do a drag
//drop if you like, it won't change the results.
rm = new RemotedWindowsMediaPlayer();
rm.Dock = System.Windows.Forms.DockStyle.Top;
panel1.Controls.Add(rm);
return;
}
private void button1_Click(object sender, EventArgs e)
{
MessageBox.Show(((WMPLib.IWMPPlayer4)rm.GetOcx()).currentMedia.sourceURL);
}
RemotedWindowsMediaPLayer.cs:
namespace RemoteWMP
{
using System;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using WMPLib;
/// <summary>
/// This is the actual Windows Media Control.
/// </summary>
[System.Windows.Forms.AxHost.ClsidAttribute("{6bf52a52-394a-11d3-b153-00c04f79faa6}")]
[ComVisible(true)]
[ClassInterface(ClassInterfaceType.AutoDispatch)]
public class RemotedWindowsMediaPlayer : System.Windows.Forms.AxHost,
IOleServiceProvider,
IOleClientSite
{
/// <summary>
/// Used to attach the appropriate interface to Windows Media Player.
/// In here, we call SetClientSite on the WMP Control, passing it
/// the dotNet container (this instance.)
/// </summary>
protected override void AttachInterfaces()
{
try
{
//Get the IOleObject for Windows Media Player.
IOleObject oleObject = this.GetOcx() as IOleObject;
if (oleObject != null)
{
//Set the Client Site for the WMP control.
oleObject.SetClientSite(this as IOleClientSite);
// Try and get the OCX as a WMP player
if (this.GetOcx() as IWMPPlayer4 == null)
{
throw new Exception(string.Format("OCX is not an IWMPPlayer4! GetType returns '{0}'",
this.GetOcx().GetType()));
}
}
else
{
throw new Exception("Failed to get WMP OCX as an IOleObject?!");
}
return;
}
catch (System.Exception ex)
{
System.Diagnostics.Debug.WriteLine(ex.ToString());
}
}
#region IOleServiceProvider Memebers - Working
/// <summary>
/// During SetClientSite, WMP calls this function to get the pointer to <see cref="RemoteHostInfo"/>.
/// </summary>
/// <param name="guidService">See MSDN for more information - we do not use this parameter.</param>
/// <param name="riid">The Guid of the desired service to be returned. For this application it will always match
/// the Guid of <see cref="IWMPRemoteMediaServices"/>.</param>
/// <returns></returns>
IntPtr IOleServiceProvider.QueryService(ref Guid guidService, ref Guid riid)
{
//If we get to here, it means Media Player is requesting our IWMPRemoteMediaServices interface
if (riid == new Guid("cbb92747-741f-44fe-ab5b-f1a48f3b2a59"))
{
IWMPRemoteMediaServices iwmp = new RemoteHostInfo();
return Marshal.GetComInterfaceForObject(iwmp, typeof(IWMPRemoteMediaServices));
}
throw new System.Runtime.InteropServices.COMException("No Interface", (int) HResults.E_NOINTERFACE);
}
#endregion
#region IOleClientSite Members
/// <summary>
/// Not in use. See MSDN for details.
/// </summary>
/// <exception cref="System.Runtime.InteropServices.COMException">E_NOTIMPL</exception>
void IOleClientSite.SaveObject()
{
throw new System.Runtime.InteropServices.COMException("Not Implemented", (int) HResults.E_NOTIMPL);
}
/// <summary>
/// Not in use. See MSDN for details.
/// </summary>
/// <exception cref="System.Runtime.InteropServices.COMException"></exception>
object IOleClientSite.GetMoniker(uint dwAssign, uint dwWhichMoniker)
{
throw new System.Runtime.InteropServices.COMException("Not Implemented", (int) HResults.E_NOTIMPL);
}
/// <summary>
/// Not in use. See MSDN for details.
/// </summary>
/// <exception cref="System.Runtime.InteropServices.COMException"></exception>
object IOleClientSite.GetContainer()
{
return (int)HResults.E_NOINTERFACE;
}
/// <summary>
/// Not in use. See MSDN for details.
/// </summary>
/// <exception cref="System.Runtime.InteropServices.COMException"></exception>
void IOleClientSite.ShowObject()
{
throw new System.Runtime.InteropServices.COMException("Not Implemented", (int) HResults.E_NOTIMPL);
}
/// <summary>
/// Not in use. See MSDN for details.
/// </summary>
/// <exception cref="System.Runtime.InteropServices.COMException"></exception>
void IOleClientSite.OnShowWindow(bool fShow)
{
throw new System.Runtime.InteropServices.COMException("Not Implemented", (int) HResults.E_NOTIMPL);
}
/// <summary>
/// Not in use. See MSDN for details.
/// </summary>
/// <exception cref="System.Runtime.InteropServices.COMException"></exception>
void IOleClientSite.RequestNewObjectLayout()
{
throw new System.Runtime.InteropServices.COMException("Not Implemented", (int) HResults.E_NOTIMPL);
}
#endregion
/// <summary>
/// Default Constructor.
/// </summary>
public RemotedWindowsMediaPlayer() :
base("6bf52a52-394a-11d3-b153-00c04f79faa6")
{
}
}
}
RemoteHostInfo.cs
using System;
namespace RemoteWMP
{
using System.Runtime.InteropServices;
/// <summary>
/// This class contains the information to return to Media Player about our remote service.
/// </summary>
[ComVisible(true)]
[ClassInterface(ClassInterfaceType.None)]
public class RemoteHostInfo :
IWMPRemoteMediaServices
{
#region IWMPRemoteMediaServices Members
/// <summary>
/// Returns "Remote" to tell media player that we want to remote the WMP application.
/// </summary>
/// <returns></returns>
public string GetServiceType()
{
return "Remote";
}
/// <summary>
/// The Application Name to show in Windows Media Player switch to menu
/// </summary>
/// <returns></returns>
public string GetApplicationName()
{
return System.Diagnostics.Process.GetCurrentProcess().ProcessName;
}
/// <summary>
/// Not in use, see MSDN for more info.
/// </summary>
/// <param name="name"></param>
/// <param name="dispatch"></param>
/// <returns></returns>
public HResults GetScriptableObject(out string name, out object dispatch)
{
name = null;
dispatch = null;
//return (int) HResults.S_OK;//NotImplemented
return HResults.E_NOTIMPL;
}
/// <summary>
/// For skins, not in use, see MSDN for more info.
/// </summary>
/// <param name="file"></param>
/// <returns></returns>
public HResults GetCustomUIMode(out string file)
{
file = null;
return HResults.E_NOTIMPL;//NotImplemented
}
#endregion
}
}
COM Interfaces.cs
using System;
namespace RemoteWMP
{
using System.Runtime.InteropServices;
#region Useful COM Enums
/// <summary>
/// Represents a collection of frequently used HRESULT values.
/// You may add more HRESULT VALUES, I've only included the ones used
/// in this project.
/// </summary>
public enum HResults
{
/// <summary>
/// HRESULT S_OK
/// </summary>
S_OK = unchecked((int)0x00000000),
/// <summary>
/// HRESULT S_FALSE
/// </summary>
S_FALSE = unchecked((int)0x00000001),
/// <summary>
/// HRESULT E_NOINTERFACE
/// </summary>
E_NOINTERFACE = unchecked((int)0x80004002),
/// <summary>
/// HRESULT E_NOTIMPL
/// </summary>
E_NOTIMPL = unchecked((int)0x80004001),
/// <summary>
/// USED CLICKED CANCEL AT SAVE PROMPT
/// </summary>
OLE_E_PROMPTSAVECANCELLED = unchecked((int)0x8004000C),
}
/// <summary>
/// Enumeration for <see cref="IOleObject.GetMiscStatus"/>
/// </summary>
public enum DVASPECT
{
/// <summary>
/// See MSDN for more information.
/// </summary>
Content = 1,
/// <summary>
/// See MSDN for more information.
/// </summary>
Thumbnail = 2,
/// <summary>
/// See MSDN for more information.
/// </summary>
Icon = 3,
/// <summary>
/// See MSDN for more information.
/// </summary>
DocPrint = 4
}
/// <summary>
/// Emumeration for <see cref="IOleObject.Close"/>
/// </summary>
public enum TAGOLECLOSE :uint{
OLECLOSE_SAVEIFDIRTY = unchecked((int)0),
OLECLOSE_NOSAVE = unchecked((int)1),
OLECLOSE_PROMPTSAVE = unchecked((int)2)
}
#endregion
#region IWMPRemoteMediaServices
/// <summary>
/// Interface used by Media Player to determine WMP Remoting status.
/// </summary>
[ComImport,
ComVisible(true),
InterfaceType(ComInterfaceType.InterfaceIsIUnknown),
Guid("CBB92747-741F-44fe-AB5B-F1A48F3B2A59")]
public interface IWMPRemoteMediaServices
{
/// <summary>
/// Service type.
/// </summary>
/// <returns><code>Remote</code> if the control is to be remoted (attached to WMP.)
/// <code>Local</code>if this is an independent WMP instance not connected to WMP application. If you want local, you shouldn't bother
/// using this control!
/// </returns>
[return: MarshalAs(UnmanagedType.BStr)]
string GetServiceType();
/// <summary>
/// Value to display in Windows Media Player Switch To Application menu option (under View.)
/// </summary>
/// <returns></returns>
[return: MarshalAs(UnmanagedType.BStr)]
string GetApplicationName();
/// <summary>
/// Not in use, see MSDN for details.
/// </summary>
/// <param name="name"></param>
/// <param name="dispatch"></param>
/// <returns></returns>
[PreserveSig]
[return: MarshalAs(UnmanagedType.U4)]
HResults GetScriptableObject([MarshalAs(UnmanagedType.BStr)] out string name,
[MarshalAs(UnmanagedType.IDispatch)] out object dispatch);
/// <summary>
/// Not in use, see MSDN for details.
/// </summary>
/// <param name="file"></param>
/// <returns></returns>
[PreserveSig]
[return: MarshalAs(UnmanagedType.U4)]
HResults GetCustomUIMode([MarshalAs(UnmanagedType.BStr)] out string file);
}
#endregion
#region IOleServiceProvider
/// <summary>
/// Interface used by Windows Media Player to return an instance of IWMPRemoteMediaServices.
/// </summary>
[ComImport,
GuidAttribute("6d5140c1-7436-11ce-8034-00aa006009fa"),
InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIUnknown),
ComVisible(true)]
public interface IOleServiceProvider
{
/// <summary>
/// Similar to QueryInterface, riid will contain the Guid of an object to return.
/// In our project we will look for <see cref="IWMPRemoteMediaServices"/> Guid and return the object
/// that implements that interface.
/// </summary>
/// <param name="guidService"></param>
/// <param name="riid">The Guid of the desired Service to provide.</param>
/// <returns>A pointer to the interface requested by the Guid.</returns>
IntPtr QueryService(ref Guid guidService, ref Guid riid);
}
/// <summary>
/// This is an example of an INCORRECT entry - do not use, unless you want your app to break.
/// </summary>
[ComImport,
GuidAttribute("6d5140c1-7436-11ce-8034-00aa006009fa"),
InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIUnknown),
ComVisible(true)]
public interface BadIOleServiceProvider
{
/// <summary>
/// This is incorrect because it causes our return interface to be boxed
/// as an object and a COM callee may not get the correct pointer.
/// </summary>
/// <param name="guidService"></param>
/// <param name="riid"></param>
/// <returns></returns>
/// <example>
/// For an example of a correct definition, look at <see cref="IOleServiceProvider"/>.
/// </example>
[return: MarshalAs(UnmanagedType.Interface)]
object QueryService(ref Guid guidService, ref Guid riid);
}
#endregion
#region IOleClientSite
/// <summary>
/// Need to implement this interface so we can pass it to <see cref="IOleObject.SetClientSite"/>.
/// All functions return E_NOTIMPL. We don't need to actually implement anything to get
/// the remoting to work.
/// </summary>
[ComImport,
ComVisible(true),
Guid("00000118-0000-0000-C000-000000000046"),
InterfaceType(ComInterfaceType.InterfaceIsIUnknown) ]
public interface IOleClientSite
{
/// <summary>
/// See MSDN for more information. Throws <see cref="COMException"/> with id of E_NOTIMPL.
/// </summary>
/// <exception cref="COMException">E_NOTIMPL</exception>
void SaveObject();
/// <summary>
/// See MSDN for more information. Throws <see cref="COMException"/> with id of E_NOTIMPL.
/// </summary>
/// <exception cref="COMException">E_NOTIMPL</exception>
[return: MarshalAs(UnmanagedType.Interface)]
object GetMoniker(uint dwAssign, uint dwWhichMoniker);
/// <summary>
/// See MSDN for more information. Throws <see cref="COMException"/> with id of E_NOTIMPL.
/// </summary>
/// <exception cref="COMException">E_NOTIMPL</exception>
[return: MarshalAs(UnmanagedType.Interface)]
object GetContainer();
/// <summary>
/// See MSDN for more information. Throws <see cref="COMException"/> with id of E_NOTIMPL.
/// </summary>
/// <exception cref="COMException">E_NOTIMPL</exception>
void ShowObject();
/// <summary>
/// See MSDN for more information. Throws <see cref="COMException"/> with id of E_NOTIMPL.
/// </summary>
/// <exception cref="COMException">E_NOTIMPL</exception>
void OnShowWindow(bool fShow);
/// <summary>
/// See MSDN for more information. Throws <see cref="COMException"/> with id of E_NOTIMPL.
/// </summary>
/// <exception cref="COMException">E_NOTIMPL</exception>
void RequestNewObjectLayout();
}
#endregion
#region IOleObject
/// <summary>
/// This interface is implemented by WMP ActiveX/COM control.
/// The only function we need is <see cref="SetClientSite"/>.
/// </summary>
[ComImport, ComVisible(true),
Guid("00000112-0000-0000-C000-000000000046"),
InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
public interface IOleObject
{
/// <summary>
/// Used to pass our custom <see cref="IOleClientSite"/> object to WMP. The object we pass must also
/// implement <see cref="IOleServiceProvider"/> to work right.
/// </summary>
/// <param name="pClientSite">The <see cref="IOleClientSite"/> to pass.</param>
void SetClientSite(IOleClientSite pClientSite);
/// <summary>
/// Implemented by Windows Media Player ActiveX control.
/// See MSDN for more information.
/// </summary>
[return: MarshalAs(UnmanagedType.Interface)]
IOleClientSite GetClientSite();
/// <summary>
/// Implemented by Windows Media Player ActiveX control.
/// See MSDN for more information.
/// </summary>
void SetHostNames(
[MarshalAs(UnmanagedType.LPWStr)]string szContainerApp,
[MarshalAs(UnmanagedType.LPWStr)]string szContainerObj);
/// <summary>
/// Implemented by Windows Media Player ActiveX control.
/// See MSDN for more information.
/// </summary>
void Close(uint dwSaveOption);
/// <summary>
/// Implemented by Windows Media Player ActiveX control.
/// See MSDN for more information.
/// </summary>
void SetMoniker(uint dwWhichMoniker, object pmk);
/// <summary>
/// Implemented by Windows Media Player ActiveX control.
/// See MSDN for more information.
/// </summary>
[return: MarshalAs(UnmanagedType.Interface)]
object GetMoniker(uint dwAssign, uint dwWhichMoniker);
/// <summary>
/// Implemented by Windows Media Player ActiveX control.
/// See MSDN for more information.
/// </summary>
void InitFromData(object pDataObject, bool fCreation, uint dwReserved);
/// <summary>
/// Implemented by Windows Media Player ActiveX control.
/// See MSDN for more information.
/// </summary>
object GetClipboardData(uint dwReserved);
/// <summary>
/// Implemented by Windows Media Player ActiveX control.
/// See MSDN for more information.
/// </summary>
void DoVerb(uint iVerb, uint lpmsg, [MarshalAs(UnmanagedType.Interface)]object pActiveSite,
uint lindex, uint hwndParent, uint lprcPosRect);
/// <summary>
/// Implemented by Windows Media Player ActiveX control.
/// See MSDN for more information.
/// </summary>
[return: MarshalAs(UnmanagedType.Interface)]
object EnumVerbs();
/// <summary>
/// Implemented by Windows Media Player ActiveX control.
/// See MSDN for more information.
/// </summary>
void Update();
/// <summary>
/// Implemented by Windows Media Player ActiveX control.
/// See MSDN for more information.
/// </summary>
[PreserveSig]
[return: MarshalAs(UnmanagedType.U4)]
HResults IsUpToDate();
/// <summary>
/// Implemented by Windows Media Player ActiveX control.
/// See MSDN for more information.
/// </summary>
Guid GetUserClassID();
/// <summary>
/// Implemented by Windows Media Player ActiveX control.
/// See MSDN for more information.
/// </summary>
[return: MarshalAs(UnmanagedType.LPWStr)]
string GetUserType(uint dwFormOfType);
/// <summary>
/// Implemented by Windows Media Player ActiveX control.
/// See MSDN for more information.
/// </summary>
void SetExtent(uint dwDrawAspect, [MarshalAs(UnmanagedType.Interface)] object psizel);
/// <summary>
/// Implemented by Windows Media Player ActiveX control.
/// See MSDN for more information.
/// </summary>
[return: MarshalAs(UnmanagedType.Interface)]
object GetExtent(uint dwDrawAspect);
/// <summary>
/// Implemented by Windows Media Player ActiveX control.
/// See MSDN for more information.
/// </summary>
uint Advise([MarshalAs(UnmanagedType.Interface)]object pAdvSink);
/// <summary>
/// Implemented by Windows Media Player ActiveX control.
/// See MSDN for more information.
/// </summary>
void Unadvise(uint dwConnection);
/// <summary>
/// Implemented by Windows Media Player ActiveX control.
/// See MSDN for more information.
/// </summary>
[return: MarshalAs(UnmanagedType.Interface)]
object EnumAdvise();
/// <summary>
/// Implemented by Windows Media Player ActiveX control.
/// See MSDN for more information.
/// </summary>
uint GetMiscStatus([MarshalAs(UnmanagedType.U4)] DVASPECT dwAspect);
/// <summary>
/// Implemented by Windows Media Player ActiveX control.
/// See MSDN for more information.
/// </summary>
void SetColorScheme([MarshalAs(UnmanagedType.Interface)] object pLogpal);
}
#endregion
}
来源：https://stackoverflow.com/questions/10957181/retrieve-song-name-from-wmp-using-c-sharp