DataTable checkbox cell does not return null but throws exception when attempting to cast value

Question

I'm having a problem with my .net application where I'm trying to take a value from a DataTable cell and cast it to a bool.
The DataTable is bound to a DataGridView and the cell is a CheckBox.
When I check if that cell is null, it returns as not null. However when I try to get the value, it returns nothing and will not cast it to a bool.

Any help appreciated.

        private void dgvItems_CellClick(object sender, DataGridViewCellEventArgs e)
        {
            if (e.ColumnIndex == 2 || e.ColumnIndex == 3)
            {
                var test = dtItems.Rows[e.RowIndex][e.ColumnIndex];               

                if (test != null)
                {
                    if ((bool)test)
                    {
                        MessageBox.Show("true");
                    }
                    else
                    {
                        MessageBox.Show("false");
                    }
                }
                else
                {
                    MessageBox.Show("null");
                }
            }
        }

Exception thrown at (bool)test:
System.InvalidCastException: 'Specified cast is not valid.'

If Dt is a DataTable being mapped, and in your database value is null and a not a Boolean, then it will show as DbNull — Code Name Jack
– Code Name Jack, Commented Sep 6, 2018 at 8:57
@PaulAlexander DBNull is a non existent value from a database learn.microsoft.com/en-us/dotnet/api/… — Hursey
– Hursey, Commented Sep 6, 2018 at 8:57

Code Name Jack · Accepted Answer · 2018-09-06 16:53:29Z

1

DataGrid Cells are ThreeWay Checkbox. They cannot be casted to bool.

Try bool? instead

  bool? testValue=(bool?) dtItems.Rows[e.RowIndex][e.ColumnIndex];    
  if (testValue!=null&&testValue)
  {
     MessageBox.Show("true");
  }
  else
  {
      MessageBox.Show("false");
  }

edited Sep 6, 2018 at 16:53

answered Sep 6, 2018 at 8:44

Code Name Jack

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3 Comments

Paul Alexander Over a year ago

throws an error: Cannot implicitly convert type 'bool?' to 'bool'. An explicit conversion exists (are you missing a cast?)

Code Name Jack Over a year ago

One question, As I rememebr, you need to dtItems.Rows[e.RowIndex][e.ColumnIndex].Value

Code Name Jack Over a year ago

I was missing the explicit cast operator (bool?).

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