XpsDocument.SignDigitally在IsSignable上抛出NullReferenceException

Question

我遇到了标题中提到的方法的问题。如果我试图签署一个XPS文档，它会运行到NullReferenceException：

at System.Windows.Xps.Packaging.XpsDocument.get_IsSignable() at System.Windows.Xps.Packaging.XpsDocument.SignDigitally(X509Certificate证书，布尔embedCertificate，XpsDigSigPartAlteringRestrictions限制，字符串signatureId，Boolean testIsSignable) at System.Windows.Xps.Packaging.XpsDocument.SignDigitally(X509Certificate证书，Boolean embedCertificate，XpsDigSigPartAlteringRestrictions限制)

任何建议都将不胜感激。

    if (sign_digitally)
    {
        UserCertificateSelector selector = new UserCertificateSelector();
        if (selector.ShowDialog() == true)
            {
                var certStore = new X509Store(StoreName.My, StoreLocation.CurrentUser);
certStore.Open(OpenFlags.ReadOnly);
#if DEBUG
                X509CertificateCollection collection = certStore.Certificates;
#else
                X509CertificateCollection collection = certStore.Certificates.Find(X509FindType.FindByThumbprint, selector.SelectedCertificate.CertificateThumbPrint,true);
#endif
                if (collection.Count > 0)
                {
                    xpsDoc.SignDigitally(collection[0], true, XpsDigSigPartAlteringRestrictions.None);
                 }
             }
         }
...

Answer 1

确保您处理的是XPS文件格式，而不是OXPS。两者都可以作为XpsDocument打开，但只有XPS可以签名。你可以检查"XpsDocument.IsSignable“标志，一旦你打开文件-对于OXPS，它将是空的。