如何在C＃中使用扩展方法？

Question

I am writing a silverlight framework plugin and I want to find my metadata in global config metadata based on the metadata key. I'm using the following statement.

var metadata = smfPlayer.GlobalConfigMetadata.FirstOrDefault(item => item.Key == METADATA_ID);

I'm getting a compilation error saying:

Error 1 'Microsoft.SilverlightMediaFramework.Utilities.Metadata.MetadataCollection' does not contain a definition for 'FirstOrDefault' and no extension method 'FirstOrDefault' accepting a first argument of type 'Microsoft.SilverlightMediaFramework.Utilities.Metadata.MetadataCollection' could be found (are you missing a using directive or an assembly reference?) C:\\cygwin\\home\\Weijia Li\\test\\testplayer\\ConvivaMMPPFPlugin\\ConvivaMMPPFPlugin.cs 45 63 ConvivaMMPPFPlugin

Can anyone tell me what's wrong with my code?

Answer 1

您是否导入了System.Linq命名空间？