ComboBox remaining blank after selected value

Question

I am writing a small application in C# using windows forms. I have a combo box that I am populating by querying a database for column names to use as the values inside the combo box. My code currently can get the values just fine, however whenever I click on the combo box it removes any text and just displays a blank 'selected option'. I have tried multiple things to correct this (changed the database field from char to varchar), tried binding to a different dataset etc. but nothing has worked. Ive also looked at other posts on this such as C# comboBox databinding - nothing happens, then it goes back to blank

Below is my code, and I believe I am doing the displaymember/valuemember part wrong however I do not understand what it is that is wrong. The column name in the database is Reason and it consists of 3 values. Any help is appreciated.

String ConnString =    ConfigurationManager.ConnectionStrings["Portal1"].ConnectionString;
SqlConnection conn = new SqlConnection(ConnString);

conn.Open();

SqlCommand sc = new SqlCommand("select [Reason] from tblReasons", conn);
SqlDataReader reader;

reader = sc.ExecuteReader();
DataTable dt = new DataTable();


dt.Columns.Add("Reason", typeof(string));

dt.Load(reader);

cboxReason.ValueMember = "Reason";
cboxReason.DisplayMember = "Reason";
cboxReason.DataSource = dt;


conn.Close();

Couple of questions, did you try without specifying cboxReason.ValueMember = "Reason"; cboxReason.DisplayMember = "Reason"; And, Are you sure there is data in "dt" — Gaurav Sharma, Mar 12 '15 at 18:46
Can you post a [minimal complete verifiable example](http://stackoverflow.com/help/mcve) because there is nothing wrong with your code. I have tried it and everything works fine - comboBox is filled and never loses its values. Perhaps you are doing something else with this comboBox? — Eugene Podskal, Mar 12 '15 at 18:50
I agree with @Eugene, it **should** work though I haven't tried it. Maybe post a screenshot of what exactly happens with the combo box? — bokibeg, Mar 12 '15 at 18:54
Thank you guys for looking at this with me. I tried the above (and below) solutions and nothing worked so I started at step 1 again. I fixed my problem, and it turns out that when created the database to draw values from I had set the type to char(50). When I changed this to varchar I forgot to manually remove all the white space created by the char. This in turn meant that when I went to grab that information from the database the return string would be to long to fit into the combo box field which made it remain blank. — G3TH, Mar 12 '15 at 19:03

Matthew Frontino · Answer 1 · 2015-03-12T20:20:03.483

Your code looks OK. I would not add the column, that should happen automatically. Here is my sample code that works:

        SqlConnection conn = new SqlConnection(ConnString);

        conn.Open();

        var reader = new SqlCommand("select ID from Users", conn).ExecuteReader();

        DataTable dt = new DataTable();
        dt.Load(reader);

        comboBox1.ValueMember = "ID";
        comboBox1.DisplayMember = "ID";
        comboBox1.DataSource = dt;
        conn.Close();

Note: This populates with the list of values in the column. For the list of column names, I would suggest changing your query to return a list of columns for the table (DB specific query) OR look at the DataTable.Columns collection for the column names.

score 0 · Answer 2 · edited May 23 '17 at 11:58

0

Did you try the answer from C# - Fill a combo box with a DataTable

cboxReason.BindingContext = this.BindingContext;

edited May 23 '17 at 11:58

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answered Mar 12 '15 at 18:49

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ComboBox remaining blank after selected value

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