Question

I have a DataGridView that is bound to a DataTable, it has a column that is a double and the values need to be between 0 and 1. Here is my code

private void dgvImpRDP_InfinityRDPLogin_CellValidating(object sender, DataGridViewCellValidatingEventArgs e)
{
    if (e.ColumnIndex == dtxtPercentageOfUsersAllowed.Index)
    {
        double percentage;
        if(dgvImpRDP_InfinityRDPLogin[e.ColumnIndex, e.RowIndex].Value.GetType() == typeof(double))
            percentage = (double)dgvImpRDP_InfinityRDPLogin[e.ColumnIndex, e.RowIndex].Value;
        else if (!double.TryParse(dgvImpRDP_InfinityRDPLogin[e.ColumnIndex, e.RowIndex].Value.ToString(), out percentage))
        {
            e.Cancel = true;
            dgvImpRDP_InfinityRDPLogin[e.ColumnIndex, e.RowIndex].ErrorText = "The value must be between 0 and 1";
            return;
        }
        if (percentage < 0 || percentage > 1)
        {
            e.Cancel = true;
            dgvImpRDP_InfinityRDPLogin[e.ColumnIndex, e.RowIndex].ErrorText = "The value must be between 0 and 1";
        }
    }
}

However my issue when dgvImpRDP_InfinityRDPLogin_CellValidating fires dgvImpRDP_InfinityRDPLogin[e.ColumnIndex, e.RowIndex].Value will contain the old value before the edit, not the new value.

For example lets say the old value was .1 and I enter 3. The above code runs when you exit the cell and dgvImpRDP_InfinityRDPLogin[e.ColumnIndex, e.RowIndex].Value will be .1 for that run, the code validates and writes 3 the data to the DataTable.

I click on it a second time, try to leave, and this time it behaves like it should, it raises the error icon for the cell and prevents me from leaving. I try to enter the correct value (say .7) but the the Value will still be 3 and there is now no way out of the cell because it is locked due to the error and my validation code will never push the new value.

Any recommendations would be greatly appreciated.

EDIT —
New version of the code based off of Stuart’s suggestion and mimicking the style the MSDN article uses. Still behaves the same.

private void dgvImpRDP_InfinityRDPLogin_CellValidating(object sender, DataGridViewCellValidatingEventArgs e)
{
    if (e.ColumnIndex == dtxtPercentageOfUsersAllowed.Index)
    {
        dgvImpRDP_InfinityRDPLogin[e.ColumnIndex, e.RowIndex].ErrorText = String.Empty;
        double percentage;
        if (!double.TryParse(dgvImpRDP_InfinityRDPLogin[e.ColumnIndex, e.RowIndex].FormattedValue.ToString(), out percentage) || percentage < 0 || percentage > 1)
        {
            e.Cancel = true;
            dgvImpRDP_InfinityRDPLogin[e.ColumnIndex, e.RowIndex].ErrorText = "The value must be between 0 and 1";
            return;
        }
    }
}

Answer 1

You need to use the FormattedValue property of the DataGridViewCellValidatingEventArgs instance instead of the cell value, as the cell value isn’t updated until validation has succeeded:

The text entered by the user through
the user interface (UI) becomes the
FormattedValue property value. This is
the value that you can validate before
it is parsed into the cell Value
property value. (MSDN)