Unable to cast object of type 'System.String' to type 'System.Byte[]'.

Question

1.00/5 (1 vote)

See more:

when i am retriving data from database i am getting following error
"Unable to cast object of type 'System.String' to type 'System.Byte[]'."

my code is

C#

cmd.CommandText = "select_student";
cmd.Parameters.AddWithValue("@sno",textBox1.Text);
da = new SqlDataAdapter(cmd);
ds = new DataSet();
da.Fill(ds, "student");
if (ds.Tables[0].Rows.Count > 0)
{
    textBox2.Text = ds.Tables[0].Rows[0][0].ToString();
    textBox3.Text = ds.Tables[0].Rows[0][1].ToString();
    if (ds.Tables[0].Rows[0][2] != System.DBNull.Value)
    {
        byte[] data = (byte[])ds.Tables[0].Rows[0][2];
        ms = new MemoryStream(data);
        pictureBox1.Image = Image.FromStream(ms);
    }
    else
        pictureBox1.Image = null;
}
else
    MessageBox.Show("Record does not exixts");

can any body help me.

[edit]Tidy code block only - OriginalGriff[/edit]

Posted 12-Nov-10 23:46pm

vijayit4all

Updated 13-Nov-10 0:05am

OriginalGriff

v2

Add a Solution

4 solutions

Solution 3

It looks like in your database you your image column
(ds.Tables[0].Rows[0][2])
has data type varchar rather than image(or varbinary(max)).
When you try to cast the string(varchar) into array of bytes it returns you the error.
If this is so it will not work.

You have to change the data type for the image column into the proper format and try the code again.

Posted 13-Nov-10 0:19am

Ed Guzman

Solution 2

If your database is holding the field as a NVCHAR or similar, then it is indeed a string. In which case use

C#

string s = (string)ds.Tables[0].Rows[0][2];
byte[] data = System.Text.Encoding.ASCII.GetBytes(s);
ms = new MemoryStream(data);
pictureBox1.Image = Image.FromStream(ms);

BTW: try not to use "magic numbers" for your code - it makes it hard to read and understand when you come back to maintain it.

Tables[0]

and

Rows[0]

are ok - ish - but

Rows[0][2]

is not as readable as

Rows[0]["DataStream"]

Posted 13-Nov-10 0:10am

OriginalGriff

Solution 4

If my database is holding the field blob,then what should i do in that case..because I am getting the error as 'unable to cast object of type system.dbnull to system.byte'

Posted 27-Mar-14 20:54pm

Raghav Gandhi

Comments

VICK 28-Mar-14 7:35am

Do post a new question to get proper help. as Already solved questions have minor chances of focus. :)

VICK 28-Mar-14 7:35am

Ah.. New CP Modification. I can reply to My OWN comment. :D

Add a Solution

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Estys · Accepted Answer · 2010-11-13T00:07:00

Solution 1

A simple cast is not enough in this case.

Try :

byte[] data = System.Text.UTF8Encoding.GetBytes(ds.Tables[0].Rows[0][2]);

I used UTF8Encoding as an example, substitute it wirh your needed encoding.

Cheers

Posted 13-Nov-10 0:07am

Estys

Unable to cast object of type 'System.String' to type 'System.Byte[]'.

4 solutions

Solution 3

Solution 1

Solution 2

Solution 4

Add your solution here

Preview 0

Unable to cast object of type 'System.String' to type 'System.Byte[]'.

4 solutions

Solution 3

Solution 1

Solution 2

Solution 4

Add your solution here

Preview 0

Existing Members

...or Join us