Question

I am having an issue with the SelectedValue control. I have first created a comboBox, and tied to it is the following method:

        private void Form1_Load(object sender, EventArgs e)
    {
        SqlCeConnection cn = new SqlCeConnection(@"Data Source = \Program Files\ParkSurvey\ParkSurvey.sdf; Persist Security Info = False; Password = *");
        cn.Open();
        SqlCeCommand cmd = cn.CreateCommand();
        cmd.CommandText = "SELECT Name FROM Cities ORDER BY Name ASC";
        SqlCeDataAdapter da = new SqlCeDataAdapter(cmd);
        DataSet ds = new DataSet();
        da.Fill(ds);
        cn.Close();
        cboCities.ValueMember = "CityId";
        cboCities.DisplayMember = "Name";
        cboCities.DataSource = ds.Tables[0];
        cboCities.SelectedIndex = -1;

    }

Assuming this is the only code I have present in my form, the comboBox (cboCities) populates accordingly. My issue arises when I try to fill a second comboBox (cboParks) with the corresponding parks associated with that city. This method looks as follows:

private void cboCities_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (cboCities.SelectedIndex > -1)
        {
            SqlCeConnection cn = new SqlCeConnection(@"Data Source = \Program Files\ParkSurvey\ParkSurvey.sdf; Persist Security Info = False; Password = *");
            cn.Open();
            SqlCeCommand cmd = cn.CreateCommand();
            cmd.CommandText = "SELECT Name FROM [Parks] WHERE CityId =" + cboCities.SelectedValue + " ORDER BY Name ASC";
            SqlCeDataAdapter da = new SqlCeDataAdapter(cmd);
            DataSet ds = new DataSet();
            da.Fill(ds);
            cn.Close();
            cboParks.ValueMember = "ParkId";
            cboParks.DisplayMember = "Name";
            cboParks.DataSource = ds.Tables[0];
            cboParks.SelectedIndex = -1;
        }
    }

When I load up my Mobile Application, the first comboBox does not populate correctly and is in fact displaying data along the lines of: “System32.Data….”, and when selecting any of them, I am brought to the runtime error that states “There was an error parsing the query. [Token line number = 1, Token line offset = 52,Token in error = Data]”. I have been lead to believe the issue itself is from the SELECT statement here:

cmd.CommandText = "SELECT Name FROM [Parks] WHERE CityId =" + cboCities.SelectedValue + " ORDER BY Name ASC";

When I change the cboCities.SelectedValue to cboCities.SelectedItem, the comboBox cboParks populates appropriately minus the filtering (it brings back ALL the data). I can also change it to simply CityId (for testing purposes) and the SELECT statement works.

I have also tried to paramertize it as such, but am brought to an entirely different error: “No mapping exists from DbType System.Data.DataRowView to a known SqlCeType.”

                cmd.CommandText = "SELECT Name FROM [Parks] WHERE CityId = @CityId ORDER BY Name ASC";
            cmd.Parameters.AddWithValue("@CityId", cboCities.SelectedValue);

Basically, what is causing SelectedValue NOT to work and bring back the appropriate CityId ValueMember of the first method? I am pulling my hair out trying to figure this out. Also, if anyone has another method of binding selected data to comboBoxes, then please do share! I’m new to the C# world so any help is much appreciated. Thank you.

Answer 1

As from MSDN,

The SelectedValue return the value of the member of the data source specified by the **ValueMember** property.

You specify as ValueMember the field CityID, but in your query this field is not present.
Therefore the SelectedValue returns the result of the ToString() method of the object.
that happens to be a System.Data.DataRowView.

I think you could resolve your problem simply adding that field to your query

So change your code in this way

using(SqlCeConnection cn = new SqlCeConnection(@"Data Source = \Program Files\ParkSurvey\ParkSurvey.sdf; Persist Security Info = False; Password = *"))
{
    cn.Open(); 
    SqlCeCommand cmd = cn.CreateCommand(); 
    cmd.CommandText = "SELECT CityID, Name FROM Cities ORDER BY Name ASC"; 
    SqlCeDataAdapter da = new SqlCeDataAdapter(cmd); 
    DataSet ds = new DataSet(); 
    da.Fill(ds); 
}        
....

then you will be able to use parameters on the second query.