将二进制图像从数据库显示到gridview中。

Question

I'm trying to retrieve binary image from database and display it in GridView control. A table called [student] in my SQL Server can be displayed inside GridView except for [Image] column. Here is my c# code trying to retrieve binary image from database:

protected void Page_Load(object sender, EventArgs e)
    {
        string constr = ConfigurationManager.ConnectionStrings["SAOSConnectionString"].ConnectionString;
        using (SqlConnection conn = new SqlConnection(constr))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter("SELECT * FROM student", conn))
            {
                DataTable dt = new DataTable();
                sda.Fill(dt);
                GridView1.DataSource = dt;
                GridView1.DataBind();
            }
        }
    }

    protected void OnRowDataBound(object sender, GridViewRowEventArgs e)
    {
        if (e.Row.RowType == DataControlRowType.DataRow)
        {
            DataRowView dr = (DataRowView)e.Row.DataItem;
            string imageUrl = "data:image/jpg;base64," + Convert.ToBase64String((byte[])dr["Image"]);
            (e.Row.FindControl("Image1") as Image).ImageUrl = imageUrl;
        }
    }

From the code above, I got an error from this line below: It said Unable to cast object of type 'System.DBNull' to type 'System.Byte[]'.

string imageUrl = "data:image/jpg;base64," + Convert.ToBase64String((byte[])dr["Image"]);

Answer 1

As the InvalidCastException message said, it is necessary to put if condition check against DBNull.Value before converting to byte array:

protected void OnRowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
        DataRowView dr = (DataRowView)e.Row.DataItem;

        if (dr["Image"] != DBNull.Value)
        {
            var imageControl = e.Row.FindControl("Image1") as Image;

            var encodedImage = Convert.ToBase64String((byte[])dr["Image"]);
            string imageUrl = "data:image/jpg;base64," + encodedImage;
            imageControl.ImageUrl = imageUrl;
        }
    }
}

Alternatively you can use Convert.IsDBNull(dr["Image"]) check which returns true if dr["Image"] contains DBNull.Value .

Answer 2

i used telerik radGrid. Please have a look. Hopefully you may find a solution

Grid Column

<telerik:GridBinaryImageColumn DataField="ImageData" ResizeMode="Fit" 
   ImageHeight="100px"
   HeaderText="Image" AlternateText="No Image" ImageWidth="100px" 
   UniqueName="ImageData">
  <HeaderStyle HorizontalAlign="Left" Width="10%" />
  <ItemStyle HorizontalAlign="Left" Font-Size="15px" />
</telerik:GridBinaryImageColumn>

C# Code

if (req["ImageData"] != DBNull.Value)
{
   byte[] imageData = (byte[])req["ImageData"];
   string base64String = Convert.ToBase64String(imageData, 0, imageData.Length);
   dtRow["ImageData"] = base64String;
   _item.ImageData = imageData;
   _items.Add(_item);
}