使用另一个组合框值过滤组合框

Question

I have three combo-box which filtering value in different tables. For the first two combo-box i have no problem but for the third combo-box, I got error show input strings was not in correct format . I using the same code for the other two and it working correctly. Can someone specify how to troubleshoot this problem?

Here my code:-

This one is for combobox two which worked perfectly:-

private void cbBridge_SelectedIndexChanged(object sender, EventArgs e)
{
    if (cbBridge.SelectedValue.ToString() != null)
    {
        int BridgeID = Convert.ToInt32(cbBridge.SelectedValue.ToString());
        FillPier(BridgeID);
    }
}

This is the code which show error

private void cbPier_SelectedIndexChanged(object sender, EventArgs e)
{
    if (cbPier.SelectedValue.ToString() != null)
    {
        int PierID = Convert.ToInt32(cbPier.SelectedValue.ToString());
        FillDataPoint(PierID);
    }
}

I hope someone can show me how to rectify this problem. Thanks.

***UPDATE****

Here the full code

 private void FillPier(int BridgeID)
    {
        SqlConnection con = new SqlConnection(conString);
        SqlCommand cmd = new SqlCommand();
        cmd.Connection = con;
        cmd.CommandType = CommandType.Text;
        cmd.CommandText = "SELECT PierID, PierName, BridgeID FROM tbPier WHERE BridgeID = @BridgeID";
        cmd.Parameters.AddWithValue("@BridgeID", BridgeID);
        DataSet objDs = new DataSet();
        SqlDataAdapter dAdapter = new SqlDataAdapter();
        dAdapter.SelectCommand = cmd;
        con.Open();
        dAdapter.Fill(objDs);
        con.Close();
        if (objDs.Tables[0].Rows.Count > 0)
        {
            cbPier.DataSource = objDs.Tables[0];
            cbPier.DisplayMember = "PierName";
            cbPier.ValueMember = "PierID";

        }

    }

    private void FillDataPoint(int PierDP)
    {
        SqlConnection con = new SqlConnection(conString);
        SqlCommand cmd = new SqlCommand();
        cmd.Connection = con;
        cmd.CommandType = CommandType.Text;
        cmd.CommandText = "SELECT PierID, InspectDate FROM tbDatapoint WHERE PierID = @PierID";
        cmd.Parameters.AddWithValue("@PierID", PierDP);
        DataSet objDs = new DataSet();
        SqlDataAdapter dAdapter = new SqlDataAdapter();
        dAdapter.SelectCommand = cmd;
        con.Open();
        dAdapter.Fill(objDs);
        con.Close();
        if (objDs.Tables[0].Rows.Count > 0)
        {
            cbInspect.DataSource = objDs.Tables[0];
            cbInspect.DisplayMember = "InspectDate";
            cbInspect.ValueMember = "PierID";
        }

    }

    private void ViewBridge_Load(object sender, EventArgs e)
    {
         FillBridge();            

    }

    private void cbBridge_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (cbBridge.SelectedValue.ToString() != null)
        {
            int BridgeID = Convert.ToInt32(cbBridge.SelectedValue.ToString());
            FillPier(BridgeID);
        }
    }


    private void cbPier_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (cbPier.SelectedIndex != 1)
        {
            int PierDP = Convert.ToInt32(cbPier.SelectedValue.ToString());
            FillDataPoint(PierDP);
        }
    }

Answer 1

Check if this can be converted to int first like this:

int x = 0
private void cbPier_SelectedIndexChanged(object sender, EventArgs e)
{
    if (Int32.TryParse(cbPier.SelectedValue.ToString(), out x))
    {
        int PierID = Convert.ToInt32(cbPier.SelectedValue.ToString());
        FillDataPoint(PierID);
    }
}

Or using the SelectedIndex property:

if(cbPier.SelectedIndex != -1)
{
   .....
}

What are the cbPier.DisplayMember and cbPier.ValueMember ? Is the diplay member the string and value member the int? Double check if that's the case first ...