How can I determine whether a checkbox is checked?

Question

private void dgvSearch_CellContentClick(object sender, DataGridViewCellEventArgs e)
        {
            if (e.ColumnIndex == colChecked1.Index)
            {
                DataGridViewCheckBoxCell checkBoxCell = dgvSearch.Rows[e.RowIndex].Cells[e.ColumnIndex] as DataGridViewCheckBoxCell;

                if ((bool)checkBoxCell.Value)
                {
                    Messager.Error("This CheckBox already checked");
                    return;
                }
            }
        }

Before the user clicks the checkbox,and if the checkbox is unchecked, the error will not be displayed.
How can I implement this ? Thank you.

Answer 1

When try to change the value of a DataGridVIew, the CurrentCellDirtyStateChanged event occurs and IsCurrentCellDirty property becomes true. At this time, when retrieve the cell value, it contains the value before the change.(However, appearance of the cell has changed.) Executing CancelEdit method cancels the changes, and executing CommitEdit method accepts the changes.

private void dgvSearch1_CurrentCellDirtyStateChanged(
                                object sender, EventArgs e) {
    var dgv = (DataGridView)sender;
    var current = dgv.CurrentCell;
    if (dgv.IsCurrentCellDirty && current != null) {
        if (current.ColumnIndex == colChecked1.Index) {
            bool prevValue = (bool)current.Value;
            if (prevValue) {
                Messager.Error("This CheckBox already checked");
                dgv.CancelEdit();
            } else {
                dgv.CommitEdit(DataGridViewDataErrorContexts.Commit);
            }
        }
    }
}

Answer 2

The CellValueChanged event seems to be suitable, because it also handles the keyboard. However, according to documentation, it is necessary to use the CurrentCellDirtyStateChanged event too:

• https://learn.microsoft.com/en-us/dotnet/api/system.windows.forms.datagridview.cellvaluechanged?#remarks

Therefore, try to remove the CellContentClick handler and use these events:

private void dgvSearch_CurrentCellDirtyStateChanged( object sender, EventArgs e )
{
    if( dgvSearch.IsCurrentCellDirty ) dgvSearch.CommitEdit( DataGridViewDataErrorContexts.Commit );
}

private void dgvSearch_CellValueChanged( object sender, DataGridViewCellEventArgs e )
{
    if( e.RowIndex >= 0 && e.ColumnIndex == colChecked1.Index )
    {
        DataGridViewCheckBoxCell checkBoxCell = dgvSearch.Rows[e.RowIndex].Cells[e.ColumnIndex] as DataGridViewCheckBoxCell;

        if( (bool)checkBoxCell.Value )
        {
            Messager.Error( "This CheckBox already checked" );
            return;
        }
    }
}