Good day!

Im developing a client server application that send dataset from the server going to client. I have successfully send my dataset from the server after converting it to xml string. My client had also successfully recieve my xml data from the server. I had also successfully load my xml data to the client dataset. Now the problem is when i try to use the column whith BLOB datatype(originaly from the server) i stuck on with this error. Unable to cast object of type 'System.String' to type 'System.Byte[]'. the line that producess this error is as follows:

        byte[] tempByte;

        for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
            tempByte = (byte[])ds.Tables[0].Rows[i]["BLOBCol"]; //erro is in this line

            //some code here

this Code is perfecly running on the server. This problem is on the client side. I do not know if the structure of my dataset had been affected when i converted it to xml and back to dataset.

Please help me.....
Thanks in advance.

The issue is that you are trying to set a byte[] to the value of the cell which is a string, this does not have a direct convert thus your cast does not work.

You will need to do a conversion first.

static byte[] GetBytes(string str)
    byte[] bytes = new byte[str.Length * sizeof(char)];
    System.Buffer.BlockCopy(str.ToCharArray(), 0, bytes, 0, bytes.Length);
    return bytes;

The above will do this for you, I have obtained it from a simple google. Here is the source post on SO, credit goes to them for it.

Edited 3 Years Ago by Mike Askew

Thanks MikeyIsMe your suggestion works but unfurtunately it cause another error. Here is my comple code for the loop. im comparing a template store on a database on a capture feature set using digital persona reader. Here it is:

DPFP.Verification.Verification ver = new DPFP.Verification.Verification();

 DPFP.Verification.Verification.Result res = new DPFP.Verification.Verification.Result();
for (int i = 0; i < ds.Tables[0].Rows.Count; i++)
    //I add here a toString Method because your parameter is in a form of a string
    tempBytes = GetBytes(ds.Tables[0].Rows[i}["BlogCol"].ToString());

    DPFP.Template template = new DPFP.Template();


    ver.Verify(FeatureSet, template, ref res); //here is the error Occurs

    if (res.Verified)

  if (!res.Verified)

      lblWarning.Text = "Failed";

        lblWarning.Text = "success";

the error says:Exception from HRESULT: 0xFFFFFFF8

silly me the solution of my problem is so simple. Here is the solution i found.

tempBytes = Convert.FromBase64String(ds.Tables[0].Rows[i]["BlogCol"].ToString());

hope this help to someone.

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