C# desktop app that failed to occupy or retrieve memory as image as output from database?

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For everyone, solve this problem, i am new in c#,
I made one desktop app, my problem is i failed to retrieve image value from database of OLEDB like MS Access.

In code i tried the textbox_keydown event that with database;

there are 5 textbox and one picturebox for image.

In textbox of barcode, i scan or enter barcode number and then fetch result from database of MS Access when i keydown that textbox.

What is my mistake?,and what to do resolve it?

The error is generated at img = (byte[])dr[5]; . the code as follow for that event.

C#

private void txtbarcode_KeyDown(object sender, KeyEventArgs e)
       {
           if (e.KeyCode == Keys.Enter)
           {
               OleDbCommand cm = new OleDbCommand("select * from stock_tab where Barcode = @Barcode",cn);
               cm.Parameters.Add(new OleDbParameter("@Barcode", txtbarcode.Text));
               cn.Open();
               OleDbDataReader dr = cm.ExecuteReader();
               while(dr.Read()){
                   txtpnm.Text = dr.GetString(1);
                   txtdesc.Text = dr.GetString(2);
                   txtqty.Text = Convert.ToString(dr.GetInt32(3));
                   txtprc.Text = Convert.ToString(dr.GetInt32(4));
                   MemoryStream m = new MemoryStream();
                   //pbproduct.Image.Save(m, pbproduct.Image.RawFormat);
                   byte[] img = (byte[])dr[5];
                   MemoryStream ms1 = new MemoryStream(img);
                   pbproduct.Image = Image.FromStream(ms1);
               }
               dr.Close();
               cn.Close();
           }
       }

What I have tried:

I tried for memory allocation of image for retrieve values from db, but error: can't cast system.DBNull type to System.Byte[]; this is error generated at: img = (byte[])dr[5];

Posted 17-Jun-16 1:15am

Member 11572517

Updated 17-Jun-16 1:38am

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OriginalGriff · Answer 1 · 2016-06-17T01:38:00

Solution 1

The error is pretty clear:

can't cast system.DBNull type to System.Byte[];

The value returned from your database isn't data - it's a null. That means that either you didn;t insert an image in that column when you saved the row, or it's the wrong column.
Given that you are using SELECT * FROM and then accessing your columns numerically starting from 1, that's the most likely.
Never use SELECT * - always list the columns you want. That way, changes in the DB column order don't make your app crash, and you don;t fecth information you don;t need.
So try:

SQL

SELECT PNM, Desc, Qty, PRC, Picture FROM Stock_tab ...

And use the name of the column to access the DataReader:

C#

if (dr.Read())
    {
    txtpnm.Text = (string) dr["PNM"];
    txtdesc.Text = (string) dr["Desc"];
    txtqty.Text = dr["Qty"].ToString();
    txtprc.Text = dr.["PRC"].ToString();
    byte[] img = (byte[])dr["Picture"];
    MemoryStream ms1 = new MemoryStream(img);
    pbproduct.Image = Image.FromStream(ms1);
    }

Posted 17-Jun-16 1:38am

OriginalGriff

Comments

Member 11572517 17-Jun-16 7:48am

thank u sir, i'll try to change according you.

Member 11572517 17-Jun-16 8:02am

Sir, according u i changed it, but the same error is generated at Memorystream ms1 = new memorystream(img);, Will error is regard of image to store in db and retrieve from it?

OriginalGriff 17-Jun-16 8:22am

What is the exact error message?

Member 11572517 17-Jun-16 10:49am

extremely sorry sir, here is holy ramazan month so, that i couldn't answered it; The error: InvalidCastException was unhandeled:
Unable to cast object of type "System.DBNull" to type "Syste.byte[]".
once again extremely sorry sir..

OriginalGriff 17-Jun-16 11:09am

That's ok - no problem.
The error message means that the value coming back from your DB is NULL - there is no image information in that field of that row.
So start there: check your DB and your insert code to find out why your DB contains nothing when you expect it to have data.
If it doesn't matter that there is no image, then compare the DB value to DBNull.Value before you try to cast it, and set a default image instead.

Member 11572517 17-Jun-16 22:17pm

Sir, in DB i used the OLE Object data type for an image field,according research on different websites, is it proper or not? may be that reason the image can't be store in db.

Member 11572517 17-Jun-16 22:17pm

Sir, in DB i used the OLE Object data type for an image field,according research on different websites, is it proper or not? may be that reason the image can't be store in db.

OriginalGriff 18-Jun-16 3:25am

Images can be stored in DB's, that's not a problem (though actually doign it can be a problem for some people):

http://www.codeproject.com/Tips/465950/Why-do-I-get-a-Parameter-is-not-valid-exception-wh

Shows how to do it for SQL Server, but the OleDb version is the same.
It's not that an image *can't* be stored in a DB - they can, and sometimes you need to - but that in at least one row you *haven't* stored an image, or anything else. That may be allowable in your system, I don't know. But if it is, then you need to code for when it happens using DBNull.Value
If it isn't, then you need to look at how the row got created without one, and then fix your DB before moving on (and remove the NULL permission from the DB Column to prevent it happening again).

Member 11572517 18-Jun-16 5:00am

I think sir, it's tough to understand, but, i'll try to understand, learn new lesson.

OriginalGriff 18-Jun-16 5:15am

That's all we can ask! :)