Reading Attribute Values from a CD or DVD

Question

Hi,

I got the code below from http://msdn.microsoft.com/en-us/library/dd564233(VS.85).aspx when I run it in Visual Studio 2005 or 2008 I get this exception: System.Windows.Forms.AxHost.InvalidActiveXStateException was unhandled. Does anyone know how I can fix this error?
                 
                using WMPLib;

        AxWMPLib.AxWindowsMediaPlayer Player;

 

        private void logDiscAttributes()

          {

           

            int iCDCount = 0; // Count of CD and DVD drives

            int iAttrCount = 0; // Attribute count.

            int iPLCount = 0; // Playlist item count. 

            IWMPCdromCollection cdCollection;

            IWMPPlaylist playlist;

            IWMPMedia media;

            string strAttribName = "";

            string strAttribValue = "";

            string strText = "";

 

            // Create a StreamWriter object to write

            // the output to a file.

            StreamWriter sw = new StreamWriter(@"c:\strOutFile.txt", true);          

            cdCollection = Player.cdromCollection;

            iCDCount = cdCollection.count; 

            // Loop through the CD and DVD drives.

            for (int i = 0; i < iCDCount; i++)

            {

                playlist = cdCollection.Item(i).Playlist;

 

                // Loop through the playlist attributes.

                iAttrCount = playlist.attributeCount;

                for (int j = 0; j < iAttrCount; j++)

                {

                    strText += "Playlist Attribute: \t";

                    strAttribName = playlist.get_attributeName(j);

                    strText += "\t" + strAttribName + "\t";

                    strAttribValue = playlist.getItemInfo(strAttribName);

                    strText += strAttribValue + "\n";

                }

 

                // Loop through the playlist.

                iPLCount = playlist.count;

                for (int k = 0; k < iPLCount; k++)

                {

                    media = playlist.get_Item(k);

 

                    // Loop through the media attributes.

                    iAttrCount = media.attributeCount;

                    for (int m = 0; m < iAttrCount; m++)

                    {

                        strText += "Track or Chapter [" + m.ToString() + "]";

                        strAttribName = media.getAttributeName(m);

                        strText += "\t" + strAttribName + "\t";

                        strText += "Read Only: " + media.isReadOnlyItem(strAttribName) + "\t";

                        strAttribValue = media.getItemInfo(strAttribName);

                        strText += strAttribValue + "\n";

                    }

                }

 

            }

             sw.Write(strText);

            sw.Close(); 

            MessageBox.Show(@"c:\strOutFile.txt" + " created");

                }

 

 

 

 

 

Answer 1

Hi,
The method logDiscAttributes()is incomplete, do you mind posting a full version of that method?
What does the exception detail say? it will be appreciated if you can provide the call stack.

Thanks,
Eric

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Answer 2

Thanks Eric,

Full version of the method below. If I run it just as it is on  http://msdn.microsoft.com/en-us/library/dd564233(VS.85).aspx I get this Error: Use of unassigned local variable 'Player'
When I change player to this: AxWMPLib.AxWindowsMediaPlayer Player = new AxWMPLib.AxWindowsMediaPlayer(); I get the call stack at the buttom of this page.

-------------------------------------------------------------------------------------------------------------------------------
using WMPLib;

AxWMPLib.AxWindowsMediaPlayer Player;


private void logDiscAttributes()

AxWMPLib.AxWindowsMediaPlayer Player;

int iCDCount = 0; // Count of CD and DVD drives

int iAttrCount = 0; // Attribute count.

int iPLCount = 0; // Playlist item count.

IWMPCdromCollection cdCollection = null;

IWMPPlaylist playlist;

IWMPMedia media;

string strAttribName = "";

string strAttribValue = "";

string strText = "";

// Create a StreamWriter object to write

// the output to a file.

StreamWriter sw = new StreamWriter(@"c:\strOutFile.txt", true);

cdCollection = Player.cdromCollection;

iCDCount = cdCollection.count;

 

 

// Loop through the CD and DVD drives.

for (int i = 0; i < iCDCount; i++)

{

playlist = cdCollection.Item(i).Playlist;

// Loop through the playlist attributes.

iAttrCount = playlist.attributeCount;

for (int j = 0; j < iAttrCount; j++)

{

strText += "Playlist Attribute: \t";

strAttribName = playlist.get_attributeName(j);

strText += "\t" + strAttribName + "\t";

strAttribValue = playlist.getItemInfo(strAttribName);

strText += strAttribValue + "\n";

}

// Loop through the playlist.

iPLCount = playlist.count;

for (int k = 0; k < iPLCount; k++)

{

media = playlist.get_Item(k);

// Loop through the media attributes.

iAttrCount = media.attributeCount;

for (int m = 0; m < iAttrCount; m++)

{

strText += "Track or Chapter [" + m.ToString() + "]";

strAttribName = media.getAttributeName(m);

strText += "\t" + strAttribName + "\t";

strText += "Read Only: " + media.isReadOnlyItem(strAttribName) + "\t";

strAttribValue = media.getItemInfo(strAttribName);

strText += strAttribValue + "\n";

}

}

}

sw.Write(strText);

sw.Close();

MessageBox.Show(@"c:\strOutFile.txt" + " created");

}

----------------------------------------------------------------------------------------

call stack:

System.Windows.Forms.AxHost.InvalidActiveXStateException was unhandled
  Message="Exception of type 'System.Windows.Forms.AxHost+InvalidActiveXStateException' was thrown."
  Source="AxInterop.WMPLib"
  StackTrace:
       at AxWMPLib.AxWindowsMediaPlayer.get_cdromCollection()
       at AttributeValuesfromaCDorDVD.Form1.logDiscAttributes() in C:\Documents and Settings\ASP\My Documents\Visual Studio 2005\Projects\AttributeValuesfromaCDorDVD\AttributeValuesfromaCDorDVD\Form1.cs:line 35
       at AttributeValuesfromaCDorDVD.Form1.button1_Click(Object sender, EventArgs e) in C:\Documents and Settings\ASP\My Documents\Visual Studio 2005\Projects\AttributeValuesfromaCDorDVD\AttributeValuesfromaCDorDVD\Form1.cs:line 90
       at System.Windows.Forms.Control.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
       at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
       at System.Windows.Forms.Control.WndProc(Message& m)
       at System.Windows.Forms.ButtonBase.WndProc(Message& m)
       at System.Windows.Forms.Button.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
       at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
       at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(Int32 dwComponentID, Int32 reason, Int32 pvLoopData)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.Run(Form mainForm)
       at AttributeValuesfromaCDorDVD.Program.Main() in C:\Documents and Settings\ASP\My Documents\Visual Studio 2005\Projects\AttributeValuesfromaCDorDVD\AttributeValuesfromaCDorDVD\Program.cs:line 17
       at System.AppDomain._nExecuteAssembly(Assembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()

Answer 3

Hi,
The exception occurred in line:
            cdCollection = Player.cdromCollection;
and the exception says the Player object has invalid state, so, beside allocate memory for Player object:
            AxWMPLib.AxWindowsMediaPlayer Player = new AxWMPLib.AxWindowsMediaPlayer();
we also need to initialize its status, something like this:
            Player.Enabled = true;
            Player.Location = new System.Drawing.Point(100, 100);
            Player.Name = "Player";
            Player.Size = new System.Drawing.Size(400, 300);
            Player.TabIndex = 0;
            Player.URL =@"E:\test.wmv";
            Player.settings.volume = 10;
            // You have to create a method mediaPlayer_PlayStateChange() to handle this event.
            Player.PlayStateChange += new AxWMPLib._WMPOCXEvents_PlayStateChangeEventHandler(mediaPlayer_PlayStateChange);
            // You have to create a method mediaPlayer_ErrorEvent() to handle this event.
            Player.ErrorEvent += new EventHandler(mediaPlayer_ErrorEvent);
Anyway, why don't use Windows Media Player Control? you can add WMP ActiveX control to a .NET application through the toolbox in VS environment, you can start from here :)

Thanks,
Eric

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Answer 4

Thanks Eric,

I will follow you suggestion.