ComboBox added programmatically to DataGridView cell not expanding on cell click

Question

I have a DataGridView in a C# WinForms project in which, when the user clicks on certain DGV cells, the cell changes to a DataGridViewComboBoxCell and the ComboBox is populated with some values for the user to select. Here's the form code for the DataGridView_Click event:

private void dgvCategories_Click(Object sender, DataGridViewCellEventArgs e)
{
    if (e.ColumnIndex == 5 && !(dgvCategories.Rows[e.RowIndex].Cells[e.ColumnIndex].GetType().Name == "DataGridViewComboBoxCell"))
    {
        // Bind combobox to dgv and than bind new values datasource to combobox
        DataGridViewComboBoxCell cboNewValueList = new DataGridViewComboBoxCell();

        // Get fields to build New Value query
        List<string> lsNewValuesResult = new List<string>();
        string strCategory = dtCategories.Rows[e.RowIndex][1].ToString();
        string strCompanyName = cboSelectCompany.Text;
        string strQueryGetNewValuesValidationInfo = "SELECT validationdb, validationtable, validationfield, validationfield2, validationvalue2" +
                                                " FROM masterfiles.categories" +
                                                " WHERE category = @category";
                                                //" WHERE category = '" + strCategory + "'";

        // Pass validation info query to db and return list of New Values
        db getListOfNewValues = new db();
        lsNewValuesResult = getListOfNewValues.GetNewValuesList(strQueryGetNewValuesValidationInfo, strCategory, strCompanyName);

        //Populate the combobox with the list of New Values
        foreach (string strListItem in lsNewValuesResult)
        {
            cboNewValueList.Items.Add(strListItem);
        }

        // 
        dgvCategories[e.ColumnIndex, e.RowIndex] = cboNewValueList;

    }
}

Here's the code in the db class that populates the ComboBox (this likely isn't necessary to include for the purposes of this question, but for the sake of completeness, I'm including it, in case is it relevant):

public List<string> GetNewValuesList(string strValidationInfoQuery, string strCategory, string strCompanyName)
{
    List<string> lsValidationInfo = new List<string>();
    List<string> lsNewValuesList = new List<string>();

    using (NpgsqlConnection conn = new NpgsqlConnection(connString))
    using (NpgsqlCommand cmd = new NpgsqlCommand(strValidationInfoQuery, conn))
    {
        cmd.Parameters.AddWithValue("category", strCategory);

        conn.Open();

        using (NpgsqlDataReader reader = cmd.ExecuteReader())
        {
            while (reader.Read())
            {
                int intReaderIndex;
                for (intReaderIndex = 0; intReaderIndex <= reader.FieldCount - 1; intReaderIndex++)
                {

                    // reader indexes 3 & 4 correspond to categories.validationfield2 and validationvalue2, which can be null
                    if (string.IsNullOrEmpty(reader[intReaderIndex].ToString()))
                    {
                        lsValidationInfo.Add("");
                    }
                    else
                    {
                        lsValidationInfo.Add(reader.GetString(intReaderIndex));
                    }
                    //Console.WriteLine("reader index " + intReaderIndex + ": " + reader.GetString(intReaderIndex));
                }
            }
        }
    }

    string strValidationDb = lsValidationInfo[0];
    string strValidationTable = lsValidationInfo[1];
    string strValidationField = lsValidationInfo[2];
    string strValidationField2 = lsValidationInfo[3];
    string strValidationValue2 = lsValidationInfo[4];

    string strQueryGetNewValues = "SELECT DISTINCT " + strValidationField +
                        " FROM " + strValidationDb + "." + strValidationTable +
                        " WHERE company_id = (SELECT id FROM company WHERE name = '" + strCompanyName + "')";

    if (!string.IsNullOrEmpty(strValidationField2) && !string.IsNullOrEmpty(strValidationValue2)) strQueryGetNewValues += " AND " + strValidationField2 + " = '" + strValidationValue2 + "'";

    strQueryGetNewValues += " ORDER BY " + strValidationField;

    using (NpgsqlConnection conn = new NpgsqlConnection(connString))
    using (NpgsqlCommand cmd = new NpgsqlCommand(strQueryGetNewValues, conn))
    {
        conn.Open();

        using (NpgsqlDataReader reader = cmd.ExecuteReader())
        {
            while (reader.Read())
            {
                int intReaderIndex;
                for (intReaderIndex = 0; intReaderIndex <= reader.FieldCount - 1; intReaderIndex++)
                {
                    // reader indexes 3 & 4 correspond to categories.validationfield2 and validationvalue2, which can be null
                    if (string.IsNullOrEmpty(reader[intReaderIndex].ToString()))
                    {
                        lsNewValuesList.Add("");
                    }
                    else
                    {
                        lsNewValuesList.Add(reader.GetString(intReaderIndex));
                    }
                    Console.WriteLine("reader index " + intReaderIndex + ": " + reader.GetString(intReaderIndex));
                }
            }
        }
    }

    return lsNewValuesList;
}

The combobox is getting populated, as I can access the items in lsNewValuesResult in the _Click method. The DGV Edit Mode is set to EditOnEnter. I tried EditOnKeystroke, but that didn't cause the combobox to expand on mouse click.

This is what the combobox looks like when the cell is clicked on and the CBO is populated and added to the DGV cell:

That's after I clicked each of the two cells.

[RESOLVED]

See my Answer below.

Unfortunately solving this revealed a new issue.

Answer 1

If I recognize your problem correctly, in my test app i add a DataGridView whit 6 column, EditMode = EditOnEnter (Others need three time click to open dropdown, As far as I tried) and handle CellStateChanged envent.

private void dgvCategories_CellStateChanged(object sender, DataGridViewCellStateChangedEventArgs e)
{
    if (e.StateChanged == DataGridViewElementStates.Selected)
    {
        DataGridViewCell cell = e.Cell;
        int columnIndex = cell.ColumnIndex;
        int rowIndex = cell.RowIndex;
        //---IF CONDITIONS--
        //columnIndex == 5
        //          Only cells in Columns[5]
        //cell.Selected
        //          Because this event raised two time, first for last selected cell and once again
        //          for currently selected cell and we need only currently selected cell.
        //cell.EditType.Name != "DataGridViewComboBoxEditingControl"
        //          If this cell "CellStateChanged" raised for second time, only other cell types allowed
        //          to edit, otherwise the current cell lost last selected item.
        if (columnIndex == 5 && cell.Selected && cell.EditType.Name != "DataGridViewComboBoxEditingControl")
        {
            DataGridViewComboBoxCell cboNewValueList = new DataGridViewComboBoxCell();

            //Add items to DataGridViewComboBoxCell for test, replace it with yours.
            for (int i = 0; i < 10; i++)
                cboNewValueList.Items.Add($"Item {i}");

            dgvCategories[columnIndex, rowIndex] = cboNewValueList;
        }
    }
}

NOTE: user must click two time in a cell to open drop down menu.

Edit One: As Reza Aghaei suggest for single click in cell:

private void dgvCategories_CellClick(object sender, DataGridViewCellEventArgs e)
{
    DataGridViewComboBoxEditingControl editingControl = dgvCategories.EditingControl as DataGridViewComboBoxEditingControl;
    if (editingControl != null)
        editingControl.DroppedDown = true;
}

Answer 2

I'm about to publicly admit that I'm stupid:

For design and functionality reasons that are required for this project, I am manually setting the widths and names of the DGV's columns, and I also need the 2nd through 4th columns ReadOnly = true. Well, I inadvertently set the 5th column - the column that this question is about to ReadOnly = true as well.

Thank you all for your attempts at answering. This just serves to remind us how something so simple can cause a seemingly big issue and is so easy to overlook!

Answer 3

You might need to turn AutoGenerateColumns off:

Also, it seems to take a three clicks for the dropdown to pop.

    public Form1()
    {
        InitializeComponent();
        dataGridView1.AutoGenerateColumns = false;
        dataGridView1.DataSource = GetDataSource();
        DataGridViewComboBoxColumn dgvcbc = new DataGridViewComboBoxColumn();
        dgvcbc.Items.Add("R0C0");
        dgvcbc.Items.Add("R1C0");
        dgvcbc.Items.Add("R2C0");
        dgvcbc.Items.Add("R3C0");
        dgvcbc.DataPropertyName = "Col0";
        dataGridView1.Columns.Add(dgvcbc);
    }

    DataTable GetDataSource()
    {
        var dtb = new DataTable();
        dtb.Columns.Add("Col0", typeof(string));
        dtb.Columns.Add("Col1", typeof(string));
        dtb.Columns.Add("Col2", typeof(string));
        dtb.Columns.Add("Col3", typeof(string));
        dtb.Columns.Add("Col4", typeof(string));
        dtb.Rows.Add("R0C0", "R0C1", "R0C2", "R0C3", "R0C4");
        dtb.Rows.Add("R1C0", "R1C1", "R1C2", "R1C3", "R1C4");
        dtb.Rows.Add("R2C0", "R2C1", "R2C2", "R2C3", "R2C4");
        dtb.Rows.Add("R3C0", "R3C1", "R3C2", "R3C3", "R3C4");
        return dtb;
    }

Answer 4

You can consider the following facts about DataGridView:

• If you set AutoGenerateColumns to false, then you need to add columns to Columns collection manually.

• If you set AutoGenerateColumns to true, when you assign the data to DataSource, the control generates columns automatically for the data source. In this case, the control looks in list of columns of the data source and for each column if there's no column in the Columns collection of the control having the same DataPropertyName as data source's column name, it will add a column to Columns collection.

• DataPropertyName of the datagridviews' columns determines the bound column of the data source.

• You usually want to add DataGridViewXXXXColumn to columns collection rather than using a DataGridViewXXXXCell for a cell.

• If you set EditMode to EditOnEnter, then if you click on dropdown button, one click is enough. If you click on cell content, two clicks is needed.

• If you would like to make it single click even if you click on cell content, take a look at this post. (Note: I haven't used this is the example, it's a bit annoying.)

• you can set DisplayStyle to Nothing, then it shows the column as a combo box, just in edit mode.

A basic example on using DataGridViewComboBoxColumn

I suppose you are going to show a list of Products having (Id, Name, Price, CategoryId) in a DataGridView and the CategoryId should come from a list of Categories having (Id, Name) and you are going to show CategoryId as a ComboBox.

In fact it's a basic and classic example of DataGridViewComboBoxColumn:

private void Form1_Load(object sender, EventArgs e) {
    var categories = GetCategories();
    var products = GetProducts();
    var idColumn = new DataGridViewTextBoxColumn() {
      Name = "Id", HeaderText = "Id", DataPropertyName = "Id"
    };
    var nameColumn = new DataGridViewTextBoxColumn() {
      Name = "Name", HeaderText = "Name", DataPropertyName = "Name"
    };
    var priceColumn = new DataGridViewTextBoxColumn() {
      Name = "Price", HeaderText = "Price", DataPropertyName = "Price"
    };
    var categoryIdColumn = new DataGridViewComboBoxColumn() {
      Name = "CategoryId", HeaderText = "Category Id", DataPropertyName = "CategoryId",
      DataSource = categories, DisplayMember = "Name", ValueMember = "Id",
      DisplayStyle = DataGridViewComboBoxDisplayStyle.Nothing
    };
    dataGridView1.Columns.AddRange(idColumn, nameColumn, priceColumn, categoryIdColumn);
    dataGridView1.EditMode = DataGridViewEditMode.EditOnEnter;
    dataGridView1.AutoGenerateColumns = false;
    dataGridView1.DataSource = products;
}
public DataTable GetProducts() {
    var products = new DataTable();
    products.Columns.Add("Id", typeof(int));
    products.Columns.Add("Name", typeof(string));
    products.Columns.Add("Price", typeof(int));
    products.Columns.Add("CategoryId", typeof(int));
    products.Rows.Add(1, "Product 1", 100, 1);
    products.Rows.Add(2, "Product 2", 200, 2);
    return products;
}
public DataTable GetCategories() {
    var categories = new DataTable();
    categories.Columns.Add("Id", typeof(int));
    categories.Columns.Add("Name", typeof(string));
    categories.Rows.Add(1, "Category 1");
    categories.Rows.Add(2, "Category 2");
    return categories;
}

Learn more

To learn more about DataGridView, take a look at DataGridView Control (Windows Forms). It contains links to some documentations and useful How To articles, including:

• DataGridView Control Overview

• Basic Column, Row, and Cell Features in the Windows Forms DataGridView Control

• Basic Formatting and Styling in the Windows Forms DataGridView Control

• Column Types in the Windows Forms DataGridView Control

Answer 5

Are you maybe getting an error which is not being shown for some reason?

If I use your code, DataGridViewComboBoxCell seems to be populated with values, but I get DataGridViewComboBoxCell value is not valid runtime error.

This test code is working fine for me:

private void dgvCategories_CellContentClick(object sender, DataGridViewCellEventArgs e)
{
    DataGridViewComboBoxCell cboNewValueList = new DataGridViewComboBoxCell();

    List<string> lsNewValuesResult = new List<string>();
    lsNewValuesResult.Add("Value1");
    lsNewValuesResult.Add("Value2");
    lsNewValuesResult.Add("Value3");

    foreach (string strListItem in lsNewValuesResult)
    {
        cboNewValueList.Items.Add(strListItem);
    }

    dgvCategories[e.ColumnIndex, e.RowIndex] = cboNewValueList;

    // Added setting of initial value
    cboNewValueList.Value = cboNewValueList.Items[0];   
}

So maybe try setting the initial value for your DataGridViewComboBoxCell after you add it to the DataGridView.