C# - Fill a combo box with a DataTable

Question

I'm used to work with Java where large amounts of examples are available. For various reasons I had to switch to C# and trying to do the following in SharpDevelop:

// Form has a menu containing a combobox added via SharpDevelop's GUI

// --- Variables
languages = new string[2];
languages[0] = "English";
languages[1] = "German";
DataSet myDataSet = new DataSet();

// --- Preparation
DataTable lTable = new DataTable("Lang");
DataColumn lName = new DataColumn("Language", typeof(string));
lTable.Columns.Add( lName );
for( int i=0; i<languages.Length; i++ ) {
    DataRow lLang = lTable.NewRow();
    lLang["Language"] = languages[i];
    lTable.Rows.Add(lLang);
}
myDataSet.Tables.Add(lTable);

// --- Handling the combobox
mnuActionLanguage.ComboBox.DataSource = myDataSet.Tables["Lang"].DefaultView;
mnuActionLanguage.ComboBox.DisplayMember = "Language";

One would assume to see some values in the dropdown, but it's empty. Please tell me what I'm doing wrong ;(

EDIT: mnuActionLanguage.ComboBox.DataBind() is what I also found on the net, but it doesn't work in my case.

SOLUTION

mnuActionLanguage.ComboBox.BindingContext = this.BindingContext;

at the end solved the problem!

Windshield

Ah, your using Windows Forms, rather than Web Forms. – Frowsty

Answer 1

You need to set the binding context of the ToolStripComboBox.ComboBox.

Here is a slightly modified version of the code that I have just recreated using Visual Studio. The menu item combo box is called toolStripComboBox1 in my case. Note the last line of code to set the binding context.

I noticed that if the combo is in the visible are of the toolstrip, the binding works without this but not when it is in a drop-down. Do you get the same problem?

If you can't get this working, drop me a line via my contact page and I will send you the project. You won't be able to load it using SharpDevelop but will with C# Express.

var languages = new string[2];
languages[0] = "English";
languages[1] = "German";

DataSet myDataSet = new DataSet();

// --- Preparation
DataTable lTable = new DataTable("Lang");
DataColumn lName = new DataColumn("Language", typeof(string));
lTable.Columns.Add(lName);

for (int i = 0; i < languages.Length; i++)
{
    DataRow lLang = lTable.NewRow();
    lLang["Language"] = languages[i];
    lTable.Rows.Add(lLang);
}
myDataSet.Tables.Add(lTable);

toolStripComboBox1.ComboBox.DataSource = myDataSet.Tables["Lang"].DefaultView;
toolStripComboBox1.ComboBox.DisplayMember = "Language";

toolStripComboBox1.ComboBox.BindingContext = this.BindingContext;

Metamathematics

Nice spot, didn't realise the combo was in a toolstrip. – Frowsty

Me either first time around ;-) – Metamathematics

Answer 2

string strConn = "Data Source=SEZSW08;Initial Catalog=Nidhi;Integrated Security=True";
SqlConnection Con = new SqlConnection(strConn);
Con.Open();
string strCmd = "select companyName from companyinfo where CompanyName='" + cmbCompName.SelectedValue + "';";
SqlDataAdapter da = new SqlDataAdapter(strCmd, Con);
DataSet ds = new DataSet();
Con.Close();
da.Fill(ds);
cmbCompName.DataSource = ds;
cmbCompName.DisplayMember = "CompanyName";
cmbCompName.ValueMember = "CompanyName";
//cmbCompName.DataBind();
cmbCompName.Enabled = true;

Fifth

You should use parameters – Chronister

Answer 3

For example, i created a table :

DataTable dt = new DataTable ();
dt.Columns.Add("Title", typeof(string));
dt.Columns.Add("Value", typeof(int));

Add recorde to table :

DataRow row = dt.NewRow();
row["Title"] = "Price"
row["Value"] = 2000;
dt.Rows.Add(row);

or :

dt.Rows.Add("Price",2000);

finally :

combo.DataSource = dt;
combo.DisplayMember = "Title";
combo.ValueMember = "Value";

Vassily

Answer 4

Are you applying a RowFilter to your DefaultView later in the code? This could change the results returned.

I would also avoid using the string as the display member if you have a direct reference the the data column I would use the object properties:

mnuActionLanguage.ComboBox.DataSource = lTable.DefaultView;
mnuActionLanguage.ComboBox.DisplayMember = lName.ColumnName;

I have tried this with a blank form and standard combo, and seems to work for me.

Frowsty

No, there is no RowFilter anywhere in the code. It seems that the issue was entirely related to the BindingContext, for whatever reason. – Windshield

Answer 5

A few points:

1) "DataBind()" is only for web apps (not windows apps).

2) Your code looks very 'JAVAish' (not a bad thing, just an observation).

Try this:

mnuActionLanguage.ComboBox.DataSource = languages;

If that doesn't work... then I'm assuming that your datasource is being stepped on somewhere else in the code.

Unessential

mnuActionLanguage.ComboBox.DataSource = languages; doesn't help either, the combobox remains empty. Tkx anyway! – Windshield

Answer 6

This line

mnuActionLanguage.ComboBox.DisplayMember = "Lang.Language";

is wrong. Change it to

mnuActionLanguage.ComboBox.DisplayMember = "Language";

and it will work (even without DataBind()).

Monoicous

Tkx Alan, I tried that too and corrected it above - but the behaviour unfortunately didn't change :( Tkx anyway! – Windshield

Well, I copy/pasted your code into VS 2008, fixed it, ran it, and I had 'English' and 'German' in the combobox. Isn't this what you needed? – Monoicous

Oh, now I see, you also ran into the BindingContext issue and fixed it yourself. Fine then :) – Monoicous