C# Winforms how to set Datagridview DataGridViewCheckBoxCell via code

Question

I am stumped on finding a solution to allow me to set a hidden DataGridViewCheckBoxCell checked state with code. The application is using a DataGridView to present a recipe on the form. Users are allowed to add/change the rows of the recipe. I want to track which rows have been changed to prompt the user for additional actions. I am using the CurrentCellDirtyStateChanged event to capture the change in state. When I try to set the cell to true or false with the following statement, it will cause an exception "Specified cast is not valid.". Note this is only occurring when I am adding a new row to the gridview. If I comment out the line below all rows added to the datagrid are indeed appended to the datatable.

ComponentsDataGridView.CurrentRow.Cells[columnIndex].Value = true

The datagrid is bound to a temp datatable and that column is added as typeof(bool). When the temp table is populated I set the column to false. I have confirmed the value is indeed false after it is populated for all the rows are appended.

In the debugger I confirmed ComponentsDataGridView.CurrentRow.Cells[columnIndex].ValueType returns the value of "Boolean".

As well I confirmed ComponentsDataGridView.CurrentRow.Cells[columnIndex].GetType() returns "System.Windows.Forms.DataGridViewCheckBoxCell" to make sure the index is correct.

The last item I checked is ComponentsDataGridView.CurrentRow.Cells[columnIndex].Value is DBNull returns true.

I have also tried setting ComponentCategoryDirty.TrueValue = true; & ComponentCategoryDirty.FalseValue = false; but it didn't make a difference.

I must be missing something, I just can't seem to find what. Is it possible to set the default state of the DataGridViewCheckBoxCell to false? Am I using the wrong event to set the value in?

Answer 1

Hi @Pat Hanks , Welcome to Microsoft Q&A,

Did you forget to set the target column to be the checkbox column?

I created a BindingList with Boolean properties as a demonstration. Use the AddButton demo to add a row with default false. Use EditButton to demonstrate modifying the boolean property of the target cell.

using System;
using System.ComponentModel;
using System.Windows.Forms;

namespace _8_29_x
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        public PersonBindingList people = new PersonBindingList();
        private void Form1_Load(object sender, EventArgs e)
        {
            people.Add(new Person(1, "a", true));
            people.Add(new Person(2, "b", false));
            people.Add(new Person(3, "c", true));
            dataGridView1.DataSource = people;

        }

        private void AddButton_Click(object sender, EventArgs e)
        {
            people.Add(new Person(people.Count + 1, "New Person", false));
        }

        private void EditButton_Click(object sender, EventArgs e)
        {
            Boolean adult = (Boolean)dataGridView1.CurrentRow.Cells["adult"].Value;
            dataGridView1.CurrentRow.Cells["adult"].Value = !adult;
        }
    }
    public class Person : INotifyPropertyChanged
    {
        public int Id { get; set; }
        private String _name;
        public String Name
        {
            get { return _name; }
            set
            {
                _name = value;
                NotifyPropertyChanged(nameof(Name));
            }
        }
        private Boolean _adult;
        public Boolean Adult
        {
            get { return _adult; }
            set
            {
                _adult = value;
                NotifyPropertyChanged(nameof(Adult));
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;
        protected void NotifyPropertyChanged(String propertyName)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }

        public Person(int id, string name, bool adult)
        {
            Id = id;
            Name = name;
            Adult = adult;
        }
    }

    public class PersonBindingList : BindingList<Person>
    {
        protected override void OnListChanged(ListChangedEventArgs e)
        {
            if (e.ListChangedType == ListChangedType.ItemAdded)
            {
                // Automatically add a new row in the DataGridView when a new item is added
                if (IsSortedCore) // Check if sorting is applied
                {
                    ApplySortCore(SortPropertyCore, SortDirectionCore); // Reapply sorting to include the new item
                }
            }
            base.OnListChanged(e);
        }
    }
}

Best Regards,

Jiale

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Answer 2

Since your using a DataTable, to set a default value use DefaultValue as shown here

DataTable dt = new DataTable();
dt.Columns.Add(new DataColumn()
{
    ColumnName = "Checked",
    DataType = typeof(bool),
    DefaultValue = false
});

In regards to setting an invisible DataGridView column value, you should use a BindingSource, set its source to the DataTable, the BindingSource is now the DataSource of the DataGridView.

The following shows

• Defining the DataTable
• Adding several rows in different styles
• Setting up the DataGridView (in this case column names are DataColumn names)
• Toggle the checkbox column value of the current row between true/false
• Toggle visibility of the checkbox column
• Raw inspection of checkbox column values
• Detect new row added, easy to expand on for other actions

Mocked code

using System.Data;
using System.Diagnostics;

#pragma warning disable CS8602 // Dereference of a possibly null reference.

namespace WinFormsApp1;

public partial class Form1 : Form
{
    private BindingSource _bindingSource = new BindingSource();
    public Form1()
    {
        InitializeComponent();

        DataTable dt = new DataTable();

        dt.Columns.Add(new DataColumn()
        {
            ColumnName = "Checked",
            DataType = typeof(bool),
            DefaultValue = false
        });
        dt.Columns.Add(new DataColumn()
        {
            ColumnName = "FirstName",
            DataType = typeof(string),
            DefaultValue = ""
        });
        dt.Columns.Add(new DataColumn()
        {
            ColumnName = "LastName",
            DataType = typeof(string),
            DefaultValue = ""
        });

        dt.Rows.Add(null, "Karen", "Payne");
        dt.Rows.Add(true, "Mary", "Jones");

        DataRow row1 = dt.NewRow();
        row1["FirstName"] = "Bill";
        row1["LastName"] = "Adams";
        dt.Rows.Add(row1);

        DataRow row2 = dt.NewRow();
        row2["FirstName"] = "Sue";
        row2["LastName"] = "Gallagher";
        row2["Checked"] = true;
        dt.Rows.Add(row2);

        dt.AcceptChanges(); // only for this demo

        _bindingSource.DataSource = dt;
        dataGridView1.DataSource = _bindingSource;
        dt.RowChanged += RowChanged;

    }

    private void ToggleColumnVisibleButton_Click(object sender, EventArgs e)
    {

        dataGridView1.Columns["Checked"]!.Visible =
            !dataGridView1.Columns["Checked"]!.Visible;
    }

    private void ToggleCheckedButton_Click(object sender, EventArgs e)
    {
        if (_bindingSource.Current is not null)
        {
            DataRow row = ((DataRowView)_bindingSource.Current).Row;
            row.SetField("Checked", 
                !row.Field<bool>("Checked"));
        }

    }

    private void InspectButton_Click(object sender, EventArgs e)
    {
        // Get at the DataTable of the BindingSource
        DataTable? table = (DataTable)_bindingSource.DataSource;

        var result = table
            .AsEnumerable()
            .Select(row => row.Field<bool>("Checked"))
            .ToList();

        foreach (var item in result)
        {
            Debug.WriteLine(item);
        }

        Debug.WriteLine("");
    }

    public void RowChanged(object sender, DataRowChangeEventArgs e)
    {
        if (e.Action != DataRowAction.Add) return;
        DataRow row = e.Row;
        // apostrophes are there in the event there is no value for first or last name
        Debug.WriteLine($"{row["Checked"]}  '{row["FirstName"]}'  '{row["LastName"]}'");
    }

    private void GetModificationsButton_Click(object sender, EventArgs e)
    {
        DataTable? table = (DataTable)_bindingSource.DataSource;
        DataTable? changedTable = table.GetChanges(DataRowState.Modified);
        if (changedTable is not null)
        {
            // there are changes, inspect the row(s) and column(s)
        }
        else
        {
            // no changes
        }
    }
}

Answer 3

I want to thank you guys for the great suggestions and knowledge. After being able to get some uninterrupted head-down time on this I was able to find a solution and what I believe was the cause of my problem. Since I was using the CurrentCellDirtyStateChanged event, at this point there is no underlying datarow of the grid row to modify yet. I checked the row count of the ComponentDataView.Table. That I believe explains why I was getting a DBNull in the checkbox value, which was generating the invalid cast exception.

Once I changed my approach to create a class object with properties that match by checkboxes I was able to set them to true/false in the CurrentCellDirtyStateChanged event.

private partial class GridRowDirtyFlags
{    
	public bool Qty { get;set; }    
	public bool Category { get; set; }    
	public bool Item { get; set; }    
	public bool UOM { get; set; }    
	public void SetFlags(bool State)    
	{        
		Qty = State;        
		Category = State;        
		Item = State;        
		UOM = State;    
	}
}

Then in the RowValidating event, I am able to update the checkbox values without incident.

I welcome any feedback on my approach.

DataGridViewRow row = ComponentsDataGridView.Rows[e.RowIndex];	
row.Cells[ComponentCategoryDirty.Index].Value = _gridRowDirtyFlags.Category;
row.Cells[ComponentItemDirty.Index].Value = _gridRowDirtyFlags.Item;
row.Cells[ComponentQtyDirty.Index].Value = _gridRowDirtyFlags.Qty;
row.Cells[ComponentUOMDirty.Index].Value = _gridRowDirtyFlags.UOM;
// reset the flags
_gridRowDirtyFlags.SetFlags(false);