Fill Combobox from database

Question

I have an error with a combobox   My code   SqlConnection conn   new SqlConnection    try       conn   new SqlConnection   Data Source SHARKAWY Initial Catalog Booking Persist Security Info True User ID sa Password 123456        string query    select FleetName  FleetID from fleets       SqlCommand cmd   new SqlCommand query  conn       cmd CommandText   query      conn Open        SqlDataReader drd   cmd ExecuteReader        while  drd Read                   cmbTripName Items Add drd  FleetName   ToString              cmbTripName ValueMember   drd  FleetID   ToString             cmbTripName DisplayMember   drd  FleetName   ToString            catch        MessageBox Show  Error         The data is presented in the combobox  but when you change the selection valuemember the displaymember does not change   It s working now but when I click the button to show the data  private void button1 Click object sender  EventArgs e        label1 Text   cmbTripName DisplayMember      label2 Text   cmbTripName ValueMember      This is displayed   FleetName FleetID  It does not display the value

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void Fillcombobox          con Open        cmd   new SqlCommand  select ID From Employees  con       Sdr   cmd ExecuteReader        while  Sdr Read                  for  int i   0  i  lt  Sdr FieldCount  i                         comboID Items Add  Sdr GetString i                         Sdr Close        con Close

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string query    quot SELECT column name FROM table name quot          query the database SqlCommand queryStatus   new SqlCommand query  myConnection   sqlDataReader reader   queryStatus ExecuteReader                                                while  reader Read        loop reader and fill the combobox   ComboBox1 Items Add reader  quot column name quot   ToString

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To use the Combobox in the way you intend  you could pass in an object to the cmbTripName Items Add method   That object should have FleetID and FleetName properties   while  drd Read          cmbTripName Items Add new Fleet drd  FleetID   ToString    drd  FleetName   ToString        cmbTripName ValueMember    FleetId   cmbTripName DisplayMember    FleetName     The Fleet Class   class Fleet        public Fleet string fleetId  string fleetName                    FleetId   fleetId             FleetName   fleetName             public string FleetId  get set        public string FleetName  get set       Or  You could probably do away with the need for a Fleet class completely by using an anonymous type     while  drd Read          cmbTripName Items Add new  FleetId   drd  FleetID   ToString    FleetName   drd  FleetName   ToString        cmbTripName ValueMember    FleetId   cmbTripName DisplayMember    FleetName

User · Answer

You will have to completely re-write your code  DisplayMember and ValueMember point to columnNames  Furthermore you should really use a using block - so the connection gets disposed  and closed  after query execution   Instead of using a dataReader to access the values I choosed a dataTable and bound it as dataSource onto the comboBox   using  SqlConnection conn   new SqlConnection   Data Source SHARKAWY Initial Catalog Booking Persist Security Info True User ID sa Password 123456          try               string query    select FleetName  FleetID from fleets           SqlDataAdapter da   new SqlDataAdapter query  conn           conn Open            DataSet ds   new DataSet            da Fill ds   Fleet            cmbTripName DisplayMember     FleetName           cmbTripName ValueMember    FleetID           cmbTripName DataSource   ds Tables  Fleet              catch  Exception ex                   write exception info to log or anything else         MessageBox Show  Error occured                              Using a dataTable may be a little bit slower than a dataReader but I do not have to create my own class  If you really have to want to make use of a DataReader you may choose  Nattrass approach  In any case you should write a using block    EDIT  If you want to get the current Value of the combobox try this  private void cmbTripName SelectedIndexChanged object sender  EventArgs e        if  cmbTripName SelectedItem    null                DataRowView drv   cmbTripName SelectedItem as DataRowView           Debug WriteLine  Item      drv Row  FleetName   ToString             Debug WriteLine  Value      drv Row  FleetID   ToString             Debug WriteLine  Value      cmbTripName SelectedValue ToString

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SqlConnection conn   new SqlConnection   Data Source TOM-PC sqlexpress Initial Catalog Northwind User ID sa Password xyz                 conn Open                SqlCommand sc   new SqlCommand  select customerid contactname from customers   conn               SqlDataReader reader               reader   sc ExecuteReader                DataTable dt   new DataTable                dt Columns Add  customerid   typeof string                dt Columns Add  contactname   typeof string                dt Load reader                comboBox1 ValueMember    customerid               comboBox1 DisplayMember    contactname               comboBox1 DataSource   dt               conn Close

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Out side the loop  set following   cmbTripName ValueMember    FleetID  cmbTripName DisplayMember    FleetName

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private void StudentForm Load object sender  EventArgs e              string q     SELECT  BatchID  FROM  Batch      BatchID column name of Batch table          SqlDataReader reader   DB Query q             while  reader Read                            cbsb Items Add reader  BatchID   ToString       cbsb is the combobox name

[c#] Fill Combobox from database

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