Weird behaviour when changing value according to ComboBoxCell selection in DataGridView bound to BindingList - Winform C#

Question

I have a form with a DataGridView (set up with the visual editor), bound to a BindingList of an EF class. One of the fields has values related to another table (selectable via ComboBox). Everything is working fine, rows were loaded, modified, added and deleted to and from de BindingList.

The problem came up when I tried to change the value of other cells in the same row according to the value selected in the combobox. I have chosen to do it in the selectedItemChange event of the ComboBoxDataGridViewEditingControl, and here is when the weird behaviour happens. If I modify the ReadOnly property of another cell it works, but when I try to modify the value of another cell, then it changes the value of the other cells, but reverts the selection of the ComboBox to the original value.

I think the problem could be related to the new selected value not persisted to the underlying BindingList, and changing the value of another cell, it loads the original value of the ComboBox.

What I have tried so far is commiting the edit before changing the value of other cells, but it didn't work as expected (first time reverts the selection, second time it change it, as if the original value was loaded before commiting the change and in the second time loads the modified value in the first attempt).

Here is a minimmum working example:

public partial class Form1 : Form
{
    BindingList<MyClass> blDatasource;
    List<MyProduct> ProductDefinitions;

    public Form1()
    {
        InitializeComponent();

        // Products datasource
        ProductDefinitions = new List<MyProduct>();
        ProductDefinitions.Add(new MyProduct(0, "CPU", 660.0));
        ProductDefinitions.Add(new MyProduct(1, "Monitor", 150.0));
        ProductDefinitions.Add(new MyProduct(2, "Mouse", 5.0));

        // MyClass datasource
        blDatasource = new BindingList<MyClass>();
        blDatasource.AllowEdit = true;
        blDatasource.AllowNew = true;
        blDatasource.AllowRemove = true;

        MyClass temp = new MyClass();
        temp.Id = 0;
        temp.ProductId = 0;
        temp.Price = 0;
        temp.Quantity = 1;
        temp.Total = 0;
        blDatasource.Add(temp);

        temp = new MyClass();
        temp.Id = 1;
        temp.ProductId = 1;
        temp.Price = 2;
        temp.Quantity = 5;
        temp.Total = 10;
        blDatasource.Add(temp);

        temp = new MyClass();
        temp.Id = 2;
        temp.ProductId = 2;
        temp.Price = 1;
        temp.Quantity = 3;
        temp.Total = 3;
        blDatasource.Add(temp);

        myClassBindingSource.DataSource = blDatasource;

        // Set up Combobox datasource
        DataTable tempProducts = new DataTable();
        tempProducts.Columns.Add("Key", typeof(int));
        tempProducts.Columns.Add("Value", typeof(string));
        int cMaxWidth = 0;

        for (int i = 0; i < ProductDefinitions.Count; i++)
        {
            DataRow r = tempProducts.NewRow();
            string cName = ProductDefinitions[i].Name;
            cMaxWidth = Math.Max(cMaxWidth, TextRenderer.MeasureText(cName, dataGridView1.Font).Width);
            r.ItemArray = new object[] { i, cName };
            tempProducts.Rows.Add(r);
        }

        // Set Comobox datasource
        productIdDataGridViewComboBoxColumn.DataSource = tempProducts;
        productIdDataGridViewComboBoxColumn.ValueMember = "Key";
        productIdDataGridViewComboBoxColumn.DisplayMember = "Value";
        productIdDataGridViewComboBoxColumn.Width = cMaxWidth + SystemInformation.VerticalScrollBarWidth + 10;
    }

    private void dataGridView1_EditingControlShowing(object sender, DataGridViewEditingControlShowingEventArgs e)
    {
        if (e.Control.GetType() == typeof(DataGridViewComboBoxEditingControl))
            ((ComboBox)e.Control).SelectionChangeCommitted += new EventHandler(comboBoxCell_SelectedChanged);
    }

    private void comboBoxCell_SelectedChanged(object sender, EventArgs e)
    {
        if (!(sender is DataGridViewComboBoxEditingControl))
            return;

        DataGridViewRow r = dataGridView1.CurrentRow;
        if (r != null)
        {
            int value = int.Parse(((DataGridViewComboBoxEditingControl)sender).SelectedValue.ToString());
            MyProduct p = ProductDefinitions.Single(x => x.Id.Equals(value));

            r.Cells[2].Value = p.Price;
            r.Cells[4].Value = p.Price * (double)((Int32)r.Cells[3].Value);
        }
    }
}

public class MyClass
{
    public int Id { get; set; }
    public int ProductId { get; set; }
    public double Price { get; set; }
    public int Quantity { get; set; }
    public double Total { get; set; }
}

public class MyProduct
{
    public int Id { get; set; }
    public string? Name { get; set; }
    public double Price { get; set; }

    public MyProduct(int id, string name, double price)
    {
        Id = id;
        Name = name;
        Price = price;
    }
}

And the relevant portion of the InitializeComponent method of designer code:

// 
// dataGridView1
// 
dataGridView1.AutoGenerateColumns = false;
dataGridView1.ColumnHeadersHeightSizeMode = DataGridViewColumnHeadersHeightSizeMode.AutoSize;
dataGridView1.Columns.AddRange(new DataGridViewColumn[] { idDataGridViewTextBoxColumn, productIdDataGridViewComboBoxColumn, priceDataGridViewTextBoxColumn, quantityDataGridViewTextBoxColumn, totalDataGridViewTextBoxColumn });
dataGridView1.DataSource = myClassBindingSource;
dataGridView1.Dock = DockStyle.Fill;
dataGridView1.Location = new Point(0, 0);
dataGridView1.Name = "dataGridView1";
dataGridView1.RowTemplate.Height = 25;
dataGridView1.Size = new Size(800, 450);
dataGridView1.TabIndex = 0;
dataGridView1.EditingControlShowing += dataGridView1_EditingControlShowing;
// 
// idDataGridViewTextBoxColumn
// 
idDataGridViewTextBoxColumn.DataPropertyName = "Id";
idDataGridViewTextBoxColumn.HeaderText = "Id";
idDataGridViewTextBoxColumn.Name = "idDataGridViewTextBoxColumn";
// 
// productIdDataGridViewComboBoxColumn
// 
productIdDataGridViewComboBoxColumn.DataPropertyName = "ProductId";
productIdDataGridViewComboBoxColumn.HeaderText = "ProductId";
productIdDataGridViewComboBoxColumn.Name = "productIdDataGridViewComboBoxColumn";
productIdDataGridViewComboBoxColumn.Resizable = DataGridViewTriState.True;
productIdDataGridViewComboBoxColumn.SortMode = DataGridViewColumnSortMode.Automatic;
// 
// priceDataGridViewTextBoxColumn
// 
priceDataGridViewTextBoxColumn.DataPropertyName = "Price";
priceDataGridViewTextBoxColumn.HeaderText = "Price";
priceDataGridViewTextBoxColumn.Name = "priceDataGridViewTextBoxColumn";
// 
// quantityDataGridViewTextBoxColumn
// 
quantityDataGridViewTextBoxColumn.DataPropertyName = "Quantity";
quantityDataGridViewTextBoxColumn.HeaderText = "Quantity";
quantityDataGridViewTextBoxColumn.Name = "quantityDataGridViewTextBoxColumn";
// 
// totalDataGridViewTextBoxColumn
// 
totalDataGridViewTextBoxColumn.DataPropertyName = "Total";
totalDataGridViewTextBoxColumn.HeaderText = "Total";
totalDataGridViewTextBoxColumn.Name = "totalDataGridViewTextBoxColumn";
// 
// myClassBindingSource
// 
myClassBindingSource.DataSource = typeof(MyClass);

If you run that code, you will notice that it changes price and total columns in the right way, but without changing the selected item (reverting to the original selection).

Thank you for your time.

UPDATE Having in mind that the problem may be the binding to datasource, I have searched in that direction, and have found BindingSource.SuspendBinding() and BindingSource.ResumeBinding(), but Microsoft's documentation tell us that this not work for Complex binding objects like DataGridView (because it does not suspend events firing, and recommends using "RaiseListChangedEvents" property of BindingSource.

I have tried the approach of in CellStartEdit and CellEndEdit event set "RaiseListChangedEvents" property of BindingSource to false and true, respectively, and it started to work, but only gets synced when combobox looses the focus.

private void dataGridView1_CellBeginEdit(object sender, DataGridViewCellCancelEventArgs e)
{
    myClassBindingSource.RaiseListChangedEvents = false;
}

private void dataGridView1_CellEndEdit(object sender, DataGridViewCellEventArgs e)
{
    myClassBindingSource.RaiseListChangedEvents = true;
}

Is there any better way of doing it?

Answer 1

One issue in dataGridView1_EditingControlShowing is that you += the event every time it's shown without -= first, so make sure there's only one event subscribed at a time. But the main "clue" to what you say about the item "reverting" seems to be that (when I run your code) the DGV is still in Edit mode after selecting the new value in the ComboBox.

That's easy to remedy. Use the SelectionChangeCommitted event to commit the edit.

private void dataGridView1_EditingControlShowing(object? sender, DataGridViewEditingControlShowingEventArgs e)
{
    if (sender is DataGridView dgv && e.Control is DataGridViewComboBoxEditingControl cb)
    {
        cb.SelectionChangeCommitted -= localOnSelectionChangeCommitted;
        cb.SelectionChangeCommitted += localOnSelectionChangeCommitted;
    }
    void localOnSelectionChangeCommitted(object? sender, EventArgs e)
    {
        BeginInvoke((MethodInvoker)delegate
        {
            dgv.EndEdit();
            if (sender is ComboBox cb && cb.SelectedItem is MyProduct product)
            {
                blDatasource[dgv.CurrentCell.RowIndex].Price = product.Price;
            }
        });
    }
}

---

Simplified Bindings

To answer the second part of your question, is there any better way of doing it I would offer these suggestions:

• Allow the DataGridView to autogenerate your columns. The only one you'll need to swap out is the ProductId column as shown below.

• Implement INotifyPropertyChanged in your MyClass and have it calculate Total when anything changes.

• Make the Total and Price properties internal so that they are read-only in the DGV.

• Bind ProductDefinitions directly to the combo box column and be done with it.

public partial class Form1 : Form
{
    List<MyProduct> ProductDefinitions;
    public Form1() => InitializeComponent();
    protected override void OnLoad(EventArgs e)
    {
        base.OnLoad(e);
        ProductDefinitions = new List<MyProduct>
        {
            new MyProduct{ Id = 0, Name = ProductType.CPU, Price = 660.0 },
            new MyProduct{ Id = 1, Name = ProductType.Monitor, Price = 150.0 },
            new MyProduct { Id = 2, Name = ProductType.Mouse, Price = 5.0 },
        };
        blDatasource = new BindingList<MyClass>
        {
            new MyClass{
                Id = 0,
                ProductId = ProductType.CPU,
                Price = ProductDefinitions.First(_=>_.Name.Equals(ProductType.CPU)).Price,
                Quantity = 1 },
            new MyClass{
                Id = 1,
                ProductId = ProductType.Monitor,
                Price = ProductDefinitions.First(_=>_.Name.Equals(ProductType.Monitor)).Price,
                Quantity = 1 },
            new MyClass{
                Id = 2,
                ProductId = ProductType.Mouse,
                Price = ProductDefinitions.First(_=>_.Name.Equals(ProductType.Mouse)).Price,
                Quantity = 1 },
        };
        dataGridView1.AutoGenerateColumns = true; // HIGHLY recommended
        dataGridView1.DataSource = blDatasource;
        DataGridViewColumn oldColumn = dataGridView1.Columns[nameof(MyClass.ProductId)];
        DataGridViewComboBoxColumn cbColumn = new DataGridViewComboBoxColumn
        {
            Name = oldColumn.Name,
            HeaderText = oldColumn.HeaderText,
        };
        int swapIndex = oldColumn.Index;
        dataGridView1.Columns.RemoveAt(swapIndex);
        dataGridView1.Columns.Insert(swapIndex, cbColumn);
        cbColumn.DataSource = ProductDefinitions;
        cbColumn.DisplayMember = "Name";
        cbColumn.DataPropertyName = nameof(MyClass.ProductId);
        dataGridView1.EditingControlShowing += dataGridView1_EditingControlShowing;
    }
    BindingList<MyClass> blDatasource;
}

MyClass

public enum ProductType
{
    CPU,
    Monitor,
    Mouse,
}
[DebuggerDisplay("{Id} {ProductId}")]
public class MyClass : INotifyPropertyChanged
{
    public int Id
    {
        get => _id;
        set
        {
            if (!Equals(_id, value))
            {
                _id = value;
                OnPropertyChanged();
            }
        }
    }
    int _id = 0;
    public ProductType ProductId
    {
        get => _productId;
        set
        {
            if (!Equals(_productId, value))
            {
                _productId = value;
                OnPropertyChanged();
            }
        }
    }
    ProductType _productId = default;
    public double Price
    {
        get => _price;
        internal set
        {
            if (!Equals(_price, value))
            {
                _price = value;
                OnPropertyChanged();
            }
        }
    }
    double _price = default;
    public int Quantity
    {
        get => _quantity;
        set
        {
            if (!Equals(_quantity, value))
            {
                _quantity = value;
                OnPropertyChanged();
            }
        }
    }
    int _quantity = default;
    public double Total
    {
        get => _total;
        internal set
        {
            if (!Equals(_total, value))
            {
                _total = value;
                OnPropertyChanged();
            }
        }
    }
    double _total = default;
    private void OnPropertyChanged([CallerMemberName]string? propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        Total = Price * Quantity;
    }
    public event PropertyChangedEventHandler? PropertyChanged;
}

---

InitializeComponent

#region Windows Form Designer generated code
/// <summary>
///  Required method for Designer support - do not modify
///  the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
    this.components = new System.ComponentModel.Container();
    this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
    this.ClientSize = new System.Drawing.Size(800, 450);
    this.Text = "Form1";
    // 
    // dataGridView1
    // 
    dataGridView1 = new DataGridView { BackgroundColor = Color.Azure };
    dataGridView1.ColumnHeadersHeightSizeMode = DataGridViewColumnHeadersHeightSizeMode.AutoSize;
    dataGridView1.Dock = DockStyle.Fill;
    dataGridView1.Location = new Point(0, 0);
    dataGridView1.Name = "dataGridView1";
    dataGridView1.Size = new Size(800, 450);
    dataGridView1.TabIndex = 0;
    this.Padding = new Padding(10);
    this.Controls.Add(dataGridView1);
}
private DataGridView dataGridView1;
#endregion