'Invalid attempt to read when no data is present.'

问题

I am working on WinForms using C#. I made a class video that has method yourvideos(). This method reads data from SQL database and add it in imagelist and listview.

First I have uploaded the image and then take the location of image using:

var=open.FileName.ToString();

Then in a function uploadvideo(), I converted image to bytearray and inserted it to database:

public void uploadvideo(string url, string path, string name,string title, DateTime date, string imgloc, string user)
        {
            con.Open();
            FileStream file = new FileStream(imgloc,FileMode.Open,FileAccess.Read);
                BinaryReader br = new BinaryReader(file);
                byte[] img = br.ReadBytes((int)file.Length);
           cmd = new SqlCommand($"insert into RecipeInfo (RecipeName, [Recipe Link],Thumbnail,Username, Date, Title) values ('{name}','{path}','@img','{user}','{date}','{title}')", con);
                        cmd.ExecuteNonQuery();
        }

and then the function yourvideos() where I am retrieving data comes.

public void yourvideos(string user, ImageList imglist, ListView list, Label l)
{
    cmd = new SqlCommand($"select Title, Thumbnail from RecipeInfo where username='{user}'", con);
    con.Open();
    SqlDataReader reader = cmd.ExecuteReader();
    if (reader.HasRows)
    {
        while (reader.HasRows)
        {
            byte[] img = (byte[])(reader[2]);
            MemoryStream ms = new MemoryStream(img);
            imglist.Images.Add(Image.FromStream(ms));
            list.Items.Add(reader[5].ToString());
            //MessageBox.Show("Data presesnt");
        }
    }
    else
    {

        l.Visible = true;
        l.Text = "Upload videos and share your recipes with others";
    }
    reader.Close();
    con.Close();
}

This function is called in the Form under the button click event

v1.yourvideos(Form2.setname, imageList1, yourvideoslistview, messagelabel);

Now, the issue is that the control enter in if statement means data is present but then it does not read data and display error:

Invalid attempt to read when no data is present.

How can I solve this issue? I showed a messagebox in order to confirm that the if statement is working and it worked, but data is not being retrieved.

回答1:

Firstly, not looking to fix your method in obtaining your data, as there are a number of issues here but you can get help on these in other SO Q's.

You can't return an index in position 5 when you are only selecting 2 columns of data.

list.Items.Add(reader[5].ToString());

Change this to something like:

list.Items.Add(reader["Title"].ToString());

Substitute 'Title' for anything else in your SELECT statement.

I would also change:

while (reader.HasRows)

while(reader.Read())

EDIT In order to fix up part of your SQL statement which will not work, I would suggest using a SQL Command Parameter. First, update this part of your Query.

username='{user}'

to this

username = @username

Next, you will need to set this as a command parameter by adding the following on the line before con.Open().

cmd.Parameters.AddWithValue("@username", user);

来源：https://stackoverflow.com/questions/63695972/invalid-attempt-to-read-when-no-data-is-present

标签

sql-server

winforms

class