c# – DataGridView CheckBox selection bug

Our app has a list of items displayed in a DataGridView. The first column is a DataGridViewCheckBoxColumn. We want our app to allow the user to click anywhere on the row as a way to select the CheckBox in the first column.

We find that if the user clicks directly on the CheckBox, selection/deselection works well. The same is true if the user clicks on the data in the other columns.

However, if the user clicks just to one side of the checkbox, we get strange behavior. The CheckBox in that row is not selected/deselected, but often another row is selected. To get a clearer picture of what is happening, you can check out my Short Video of the buggy behavior.

I tried setting some breakpoints in the code, for example, on our SelectionChanged handler, our CellClick handler and our CellValueChanged handler. I find these breakpoints are hit in the same pattern, regardless of whether I click on the CheckBox, just to one side of the checkbox or on the data in the other columns.

Has anyone seen behavior like this? Any ideas what may be going on? Is it a bug in the .NET DataGridView code, or is there something I should look for in our code?

Here is the relevant code, as requested (or you can download a ZIP file with the complete solution)…

From Form1.cs:

public Form1()
{
    InitializeComponent();
    dgsControl.SetUp();
}

From Form1.Designer.cs:

private void InitializeComponent()
{
    this.components = new System.ComponentModel.Container();
    this.dgsControl = new DGSelection();
    this.Controls.Add(this.dgsControl);
    // 
    // dgsControl
    // 
    this.dgsControl.Dock = System.Windows.Forms.DockStyle.Fill;
    this.dgsControl.Location = new System.Drawing.Point(3, 3);
    this.dgsControl.Margin = new System.Windows.Forms.Padding(2, 2, 2, 2);
    this.dgsControl.Name = "dgsControl";
    this.dgsControl.Size = new System.Drawing.Size(689, 325);
    this.dgsControl.TabIndex = 0;

    this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
    this.ClientSize = new System.Drawing.Size(800, 450);
    this.Text = "DataGridView Demo";
}

From DGSelection.cs:

public partial class DGSelection : UserControl
{
    #region Member variables

    private class ListData
    {
        public string Option;
        public string Description;
    }
    private static readonly List<ListData> TestData = new List<ListData>
    {
        new ListData { Option = "Option1", Description = "Description1" },
        new ListData { Option = "Option2", Description = "Description2" },
        new ListData { Option = "Option3", Description = "Description3" },
        new ListData { Option = "Option4", Description = "Description4" }
    };

    public event EventHandler OptionsChanged;
    #endregion

    #region Constructor
    public DGSelection()
    {
        InitializeComponent();
        dgvTable.BackgroundColor = Color.DarkGray;
        dgvTable.DefaultCellStyle.BackColor = Color.DarkGray;
        dgvTable.DefaultCellStyle.ForeColor = Color.Black;
        dgvTable.ColumnHeadersDefaultCellStyle.BackColor = Color.DarkGray;
        dgvTable.ColumnHeadersDefaultCellStyle.ForeColor = Color.Black;
        dgvTable.GridColor = Color.DarkGray;
        cbxCheckAll.BackColor = Color.DarkGray;

        // Move label where it belongs (moved elsewhere in Designer for ease of editing).
        lbl_empty.Top = Top + 5;
    }
    #endregion

    #region Public Methods
    public void SetUp()
    {
        dgvTable.Rows.Clear();
        cbxCheckAll.Checked = false;
        bool anyRows = TestData.Any();
        lbl_empty.Visible = !anyRows;
        cbxCheckAll.Visible = anyRows;
        dgvTable.ColumnHeadersVisible = anyRows;

        foreach (ListData ld in TestData)
        {
            dgvTable.Rows.Add(false, ld.Option, ld.Description);
        }
    }
    #endregion

    #region Event Handlers
    private void DGSelection_SelectionChanged(object sender, EventArgs e)
    {
        dgvTable.ClearSelection();
    }

    private void cbxCheckAll_CheckedChanged(object sender, EventArgs e)
    {
        try
        {
            dgvTable.CellValueChanged -= DgvTableCellValueChanged;
            bool checkAll = cbxCheckAll.Checked;
            foreach (DataGridViewRow row in dgvTable.Rows)
                row.Cells[0].Value = checkAll;
        }
        finally
        {
            dgvTable.CellValueChanged += DgvTableCellValueChanged;
        }
        OptionsChanged?.Invoke(this, EventArgs.Empty);
    }

    private void DGSelection_CellClick(object sender, DataGridViewCellEventArgs e)
    {
        if (e.RowIndex < 0)
            return; // Ignore clicks in the header row

        DataGridViewCell checkBoxCell = dgvTable.Rows[e.RowIndex].Cells[0];
        checkBoxCell.Value = !(bool)checkBoxCell.Value;
    }

    private void DgvTableCellValueChanged(object sender, DataGridViewCellEventArgs e)
    {
        try
        {
            cbxCheckAll.CheckedChanged -= cbxCheckAll_CheckedChanged;
            cbxCheckAll.CheckedChanged -= cbxCheckAll_CheckedChanged;
            // Not sure why, but sometimes subscribed twice

            bool checkAll = dgvTable.Rows.Count > 0;
            foreach (DataGridViewRow row in dgvTable.Rows)
                checkAll &= row.Cells[0].Value.Equals(true);
            cbxCheckAll.Checked = checkAll;
        }
        finally
        {
            cbxCheckAll.CheckedChanged += cbxCheckAll_CheckedChanged;
        }
        OptionsChanged?.Invoke(this, EventArgs.Empty);
    }

    private void DGSelection_CurrentCellDirtyStateChanged(object sender, EventArgs e)
    {
        dgvTable.CommitEdit(DataGridViewDataErrorContexts.Commit);
    }
    #endregion
}

From DGSelection.Designer.cs:

private void InitializeComponent()
{
    components = new System.ComponentModel.Container();
    System.Windows.Forms.DataGridViewCellStyle dataGridViewCellStyle1 = new System.Windows.Forms.DataGridViewCellStyle();
    System.Windows.Forms.DataGridViewCellStyle dataGridViewCellStyle2 = new System.Windows.Forms.DataGridViewCellStyle();
    System.Windows.Forms.DataGridViewCellStyle dataGridViewCellStyle3 = new System.Windows.Forms.DataGridViewCellStyle();
    this.dgvTable = new System.Windows.Forms.DataGridView();
    this.colCheckboxes = new System.Windows.Forms.DataGridViewCheckBoxColumn();
    this.colText1 = new System.Windows.Forms.DataGridViewTextBoxColumn();
    this.colText2 = new System.Windows.Forms.DataGridViewTextBoxColumn();
    this.cbxCheckAll = new System.Windows.Forms.CheckBox();
    this.lbl_empty = new System.Windows.Forms.Label();
    ((System.ComponentModel.ISupportInitialize)(this.dgvTable)).BeginInit();
    this.SuspendLayout();
    // 
    // dgvTable
    // 
    this.dgvTable.AllowUserToAddRows = false;
    this.dgvTable.AllowUserToDeleteRows = false;
    this.dgvTable.AllowUserToResizeColumns = false;
    this.dgvTable.AllowUserToResizeRows = false;
    this.dgvTable.AutoSizeRowsMode = System.Windows.Forms.DataGridViewAutoSizeRowsMode.AllCells;
    this.dgvTable.BackgroundColor = System.Drawing.SystemColors.Window;
    this.dgvTable.BorderStyle = System.Windows.Forms.BorderStyle.None;
    this.dgvTable.CellBorderStyle = System.Windows.Forms.DataGridViewCellBorderStyle.None;
    this.dgvTable.ColumnHeadersBorderStyle = System.Windows.Forms.DataGridViewHeaderBorderStyle.Single;
    dataGridViewCellStyle1.Alignment = System.Windows.Forms.DataGridViewContentAlignment.MiddleLeft;
    dataGridViewCellStyle1.BackColor = System.Drawing.SystemColors.ControlDark;
    dataGridViewCellStyle1.Font = new System.Drawing.Font("Microsoft Sans Serif", 8.25F, System.Drawing.FontStyle.Bold, System.Drawing.GraphicsUnit.Point, ((byte)(0)));
    dataGridViewCellStyle1.ForeColor = System.Drawing.SystemColors.WindowText;
    dataGridViewCellStyle1.Padding = new System.Windows.Forms.Padding(3);
    dataGridViewCellStyle1.SelectionBackColor = System.Drawing.SystemColors.Highlight;
    dataGridViewCellStyle1.SelectionForeColor = System.Drawing.SystemColors.HighlightText;
    dataGridViewCellStyle1.WrapMode = System.Windows.Forms.DataGridViewTriState.True;
    this.dgvTable.ColumnHeadersDefaultCellStyle = dataGridViewCellStyle1;
    this.dgvTable.ColumnHeadersHeightSizeMode = System.Windows.Forms.DataGridViewColumnHeadersHeightSizeMode.AutoSize;
    this.dgvTable.Columns.AddRange(new System.Windows.Forms.DataGridViewColumn[] {
        this.colCheckboxes,
        this.colText1,
        this.colText2 });
    this.dgvTable.Dock = System.Windows.Forms.DockStyle.Fill;
    this.dgvTable.EditMode = System.Windows.Forms.DataGridViewEditMode.EditOnEnter;
    this.dgvTable.EnableHeadersVisualStyles = false;
    this.dgvTable.Location = new System.Drawing.Point(0, 0);
    this.dgvTable.Margin = new System.Windows.Forms.Padding(2);
    this.dgvTable.MultiSelect = false;
    this.dgvTable.Name = "dgvTable";
    this.dgvTable.RowHeadersVisible = false;
    this.dgvTable.RowTemplate.Height = 24;
    this.dgvTable.ScrollBars = System.Windows.Forms.ScrollBars.Vertical;
    this.dgvTable.SelectionMode = System.Windows.Forms.DataGridViewSelectionMode.CellSelect;
    this.dgvTable.Size = new System.Drawing.Size(484, 318);
    this.dgvTable.TabIndex = 0;
    this.dgvTable.CellClick += new System.Windows.Forms.DataGridViewCellEventHandler(this.DGSelection_CellClick);
    this.dgvTable.CellValueChanged += new System.Windows.Forms.DataGridViewCellEventHandler(this.DgvTableCellValueChanged);
    this.dgvTable.CurrentCellDirtyStateChanged += new System.EventHandler(this.DGSelection_CurrentCellDirtyStateChanged);
    this.dgvTable.SelectionChanged += new System.EventHandler(this.DGSelection_SelectionChanged);
    // 
    // colCheckboxes
    // 
    this.colCheckboxes.AutoSizeMode = System.Windows.Forms.DataGridViewAutoSizeColumnMode.None;
    this.colCheckboxes.Frozen = true;
    this.colCheckboxes.HeaderText = "";
    this.colCheckboxes.Name = "colCheckboxes";
    this.colCheckboxes.Resizable = System.Windows.Forms.DataGridViewTriState.False;
    this.colCheckboxes.Width = 30;
    // 
    // colText1
    // 
    this.colText1.AutoSizeMode = System.Windows.Forms.DataGridViewAutoSizeColumnMode.AllCells;
    dataGridViewCellStyle2.Padding = new System.Windows.Forms.Padding(5, 0, 0, 0);
    this.colText1.DefaultCellStyle = dataGridViewCellStyle2;
    this.colText1.HeaderText = "Option";
    this.colText1.Name = "colText1";
    this.colText1.ReadOnly = true;
    this.colText1.Resizable = System.Windows.Forms.DataGridViewTriState.False;
    this.colText1.SortMode = System.Windows.Forms.DataGridViewColumnSortMode.NotSortable;
    this.colText1.Width = 57;
    // 
    // colText2
    // 
    this.colText2.AutoSizeMode = System.Windows.Forms.DataGridViewAutoSizeColumnMode.Fill;
    dataGridViewCellStyle3.Padding = new System.Windows.Forms.Padding(5, 0, 0, 0);
    this.colText2.DefaultCellStyle = dataGridViewCellStyle3;
    this.colText2.HeaderText = "Description";
    this.colText2.Name = "colText2";
    this.colText2.ReadOnly = true;
    this.colText2.Resizable = System.Windows.Forms.DataGridViewTriState.False;
    this.colText2.SortMode = System.Windows.Forms.DataGridViewColumnSortMode.NotSortable;
    // 
    // cbxCheckAll
    // 
    this.cbxCheckAll.AutoSize = true;
    this.cbxCheckAll.BackColor = System.Drawing.SystemColors.ControlDark;
    this.cbxCheckAll.Location = new System.Drawing.Point(8, 5);
    this.cbxCheckAll.Margin = new System.Windows.Forms.Padding(2);
    this.cbxCheckAll.Name = "cbxCheckAll";
    this.cbxCheckAll.Size = new System.Drawing.Size(15, 14);
    this.cbxCheckAll.TabIndex = 1;
    this.cbxCheckAll.UseVisualStyleBackColor = false;
    this.cbxCheckAll.CheckedChanged += new System.EventHandler(this.cbxCheckAll_CheckedChanged);
    // 
    // lbl_empty
    // 
    this.lbl_empty.Anchor = ((System.Windows.Forms.AnchorStyles)
        (((System.Windows.Forms.AnchorStyles.Top |
           System.Windows.Forms.AnchorStyles.Left) |
           System.Windows.Forms.AnchorStyles.Right)));
    this.lbl_empty.BackColor = System.Drawing.Color.Transparent;
    this.lbl_empty.Location = new System.Drawing.Point(3, 25);
    this.lbl_empty.Name = "lbl_empty";
    this.lbl_empty.Size = new System.Drawing.Size(478, 44);
    this.lbl_empty.TabIndex = 2;
    this.lbl_empty.Text = "No data defined for the list";
    this.lbl_empty.Visible = false;
    // 
    // DGSelection
    // 
    this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
    this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
    this.Controls.Add(this.lbl_empty);
    this.Controls.Add(this.cbxCheckAll);
    this.Controls.Add(this.dgvTable);
    this.Margin = new System.Windows.Forms.Padding(2);
    this.Name = "DGSelectionControl";
    this.Size = new System.Drawing.Size(484, 318);
    ((System.ComponentModel.ISupportInitialize)(this.dgvTable)).EndInit();
    this.ResumeLayout(false);
    this.PerformLayout();
}

Is there something in our code which is causing this behavior? Or is it a bug in the implementation of DataGridView? I have reproduced this with both .NET Framework v.4.6 & v.4.8.

(Note: reposted from Microsoft Q&A Forum, since I got no responses there.)

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