在填充数组时未处理nullreferenceexception-C＃

Question

I am trying to retrieve all names that was saved at the sql database
then suddenly I got the

nullreferenceexception was unhandled on filling up array - Object reference not set to an instance of an object.

this was my code:

I got the error at the

  imgName[i] = Convert.ToString(dt.Rows[i]["FinalImageName"]);  

in that part, I'd like to fill imgName array all the name

how could i fix it?, help please

string c_string = "server=.\\sqlexpress;database=Blue;trusted_connection=true";

public static string ImageToShow;
private int NumOfFiles;
private string[] imgName;

SqlConnection c = new SqlConnection(c_string);
//SqlCommand cm = new SqlCommand(cmd,c);

private void frmMain_Load(object sender, EventArgs e) {
    SqlConnection c = new SqlConnection(c_string);

    try {
        c.Open();
    }
    catch (SqlException ee) {
        MessageBox.Show(ee.Message);
    }
    finally {
        c.Close();
    }
    updateData();
}

private void updateData() {

    SqlConnection c = new SqlConnection(c_string);

    SqlDataAdapter da = new SqlDataAdapter("SELECT * FROM FinalImages", c);

    DataTable dt = new DataTable();
    da.Fill(dt);

    NumOfFiles = dt.Rows.Count;
    for (int i = 0; i < dt.Rows.Count; i++) {
        imgName[i] = Convert.ToString(dt.Rows[i]["FinalImageName"]);

    }
}​

Answer 1

You need to instantiate the imgName array .

private void updateData()
{
    {

        SqlConnection c = new SqlConnection(c_string);

        SqlDataAdapter da = new SqlDataAdapter("SELECT * FROM FinalImages", c);

        DataTable dt = new DataTable();
        da.Fill(dt);

        NumOfFiles = dt.Rows.Count;
        imgName = new string[NumOfFiles];
        for (int i = 0; i < NumOfFiles; i++)
        {
            imgName[i] = Convert.ToString(dt.Rows[i]["FinalImageName"]);

        } 
    }
}

Answer 2

That is because you have not specified the size of array... either specify size of array or use arraylist / generic list

Try this: include namespace : using System.Collections.Generic;

string c_string = "server=.\\sqlexpress;database=Blue;trusted_connection=true";

    public static string ImageToShow; 
    private int NumOfFiles;
    //private string[] imgName;
   List<string> imgName= new List<string>();

SqlConnection c = new SqlConnection(c_string);
        //SqlCommand cm = new SqlCommand(cmd,c);


   private void frmMain_Load(object sender, EventArgs e)
    {
        SqlConnection c = new SqlConnection(c_string);

        try
        {
            c.Open();
        }
        catch (SqlException ee)
        {
            MessageBox.Show(ee.Message);
        }
        finally
        {
            c.Close();
        }
        updateData();
    }

private void updateData()
    {

        SqlConnection c = new SqlConnection(c_string);

        SqlDataAdapter da = new SqlDataAdapter("SELECT * FROM FinalImages", c);

        DataTable dt = new DataTable();
        da.Fill(dt);

        NumOfFiles = dt.Rows.Count;
        for (int i = 0; i < dt.Rows.Count; i++)
        {
           // imgName[i] = Convert.ToString(dt.Rows[i]["FinalImageName"]);
           imgName.Add(Convert.ToString(dt.Rows[i]["FinalImageName"]));
        } 
    }

Answer 3

You haven't created an array, you have only created the variable that can hold the reference to the array.

Create the array once you know how many rows there are:

imgName = new string[dt.Rows.Count];