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I need to figure out whether a document is modified in a document library (and not its properties). is it possible to use an event receiver to compute the hash of the document before it is updated and after its updated ? Please share the code along with the references if any.....

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You can compare the BeforeProperties and AfterProperties of an event receiver to check for any changes in the properties.

Related question here

Code would be something like this:

    // ItemUpdated
    public override void ItemUpdated(SPItemEventProperties properties)
    {
        base.ItemUpdated(properties);
        if (!EqualProperties(properties.AfterProperties,properties.BeforeProperties))
        { 

        }
    }

Where EqualProperties is a method which compares the collections.

If you want to compare hashvalues you can create a text column to store the hash.

    public override void ItemAdded(SPItemEventProperties properties)
    {
        base.ItemAdded(properties);
        this.DisableEventFiring();
        properties.ListItem["myCustomField"] = this.CalculateHash(properties.ListItem.File);
        properties.ListItem.SystemUpdate();
        this.EnableEventFiring();
    }

    public override void ItemUpdated(SPItemEventProperties properties)
    {
        this.DisableEventFiring();
        properties.ListItem["myCustomField"] = this.CalculateHash(properties.ListItem.File);
        properties.ListItem.SystemUpdate();
        this.EnableEventFiring();
        base.ItemUpdated(properties);
        if (properties.ListItem["myCustomField"] != properties.BeforeProperties["myCustomField"])
        { 

        }
    }
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  • Thanks Anima, but my major concern is to determine whether the document content is modified or not. – Vish Dec 4 '13 at 9:50
  • Updated the code. You can use the OpenBinaryStream method on the SPFile object and use the stream to create a hash value with the type System.Security.Cryptography.MD5 which exposes a ComputeHash() method. – Gert Braspenning Dec 4 '13 at 10:17
  • Which reference/namespace is needed to use the CalculateHash() method ? or is it a user-defined method ? – Vish Dec 4 '13 at 10:34
  • More information. The namespace is System.Security.Cryptography. – Gert Braspenning Dec 4 '13 at 10:39
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    try
               {
                   this.EventFiringEnabled = false;
                   SPListItem CurrentItem = properties.ListItem;
                   SPFile doc = CurrentItem.File;
                   //Stream stream = doc.OpenBinaryStream(

                   MD5 md5 = new MD5CryptoServiceProvider();

                    /* Calculate Hash */
                   byte[] hash1 = md5.ComputeHash(doc.OpenBinary()); //doc.OpenBinary() returns byte[]




                   /* Show Hash in TextBoxes */
                   CurrentItem["CustomFieldName"] = BitConverter.ToString(hash1); 

                   CurrentItem.Update();
               }
               finally
               {
                   this.EventFiringEnabled = true;
               }

Need to include the System.Security.Cryptography namespace. Also include the following tag in the elements.xml file before end of Receiver tag :

    <Synchronization>Synchronous</Synchronization>

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