Unable to add attributes to media metadata

Question

Hi I am trying to add attributes to media metadata. I am using iwmheaderinfo3.AddAttribute for adding the attribute. The code gives no error. But the attributes are not adding. Any help would be well appreciated. Thanks In advance. nnair.

neethi nair · Answer

Hi Sorry for the late reply sir. The error was because I made an instance of metadataeditor twice which set a null valu for it second time. I had met with some other exception after that saying Value is out of expected range. While debugging the values passed in all were correct. The windows media COM is imported in the ComWrapper class which I created instead of just referencing the wrapper class. I had declared just the functions which I needed in the wrapper class. But when we use an interface importing a COM we need to declare all the functions in it in the wrapper class and use the functions which we need. Also the functions should be in order which its declared in the original wrapper class. Otherwise it will take the wrong function. This happened in my case. The details of this is specified in my previous post. Hope this would help you. Thanks a lot. nnair

Bechir Bejaoui · Answer

Could you more explain the issue with more details?

neethi nair · Answer

Well solved it. I was using my own ComWrapper not the one provided by SDK. When declaring COM interfaces in .NET you cannot simply pick and choose what methods you want. All the methods needed to be declared and it needs to be in order. COM Interfaces cannot include any interfaces in their base interface list and they must declare the interface member functions in the order tht the methods appear in the COM Interface. COM interfaces declared in c# must include declarations of all the members of their base interfaces with the exception of members of IUnknown and IDispatch..dotnet framework automatically adds these! Hope this will help anyone who have the problem. Thanks for your help sir.

neethi nair · Answer

I tried with StringBuider as you suggested still the same exception... Object reference not set to instance of an object. In the stack trace it says its caused at the AddAttribute call.

Bechir Bejaoui · Answer

Try to use string builder instead of string within your code I have a doubt about the string

neethi nair · Answer

Hi Bechir Thanks for the link. I used this msdn site to find out how to add media attributes. I checked with so many blogs too. The message in the catch section I got is Object is not set to instance of an object. But I am not passing any null values to the interface function. In the ComWrapper I have declared it in the way below: void AddAttribute( [ In ] ushort wStreamNum [ In  MarshalAs ( UnmanagedType .LPWStr)] string pszName [ Out ] out ushort pwIndex [ In ] WMT_ATTR_DATATYPE Type [ In ] ushort wLangIndex [ In  MarshalAs ( UnmanagedType .LPArray)] byte [] pValue [ In ] uint dwlength); All the values are being passed correctly. I am now trying to find whether somewhere its setting some null values. Reg Nnair

Bechir Bejaoui · Answer

http://msdn.microsoft.com/en-us/library/aa388373(VS.85).aspx please read the remarque section may you have a such case