我的GD库是否打开？(Is my GD library turned on or not?)

 此问题在以下MSDN论坛发布： DataGridView + RowValidating = Index 4没有值？ 
 
 基本上，DataGridView处理验证的方式似乎是一个错误（或者至少非常意外的行为） - MessageBox.Show（）导致不再存在的行上的验证。 
 
 我发现以下对代码的更改修复了这个问题： 
 
private void myGrid_RowValidating(object sender, DataGridViewCellCancelEventArgs e) 
{ 
    // Note the check to see if the current row is dirty
    if (string.IsNullOrEmpty(myGrid.Rows[e.RowIndex].Cells["MandatoryColumn"].FormattedValue.ToString()) &&  myGrid.IsCurrentRowDirty) 
    { 
        e.Cancel = true; 
        myGrid.Rows[e.RowIndex].Cells["MandatoryColumn"].ErrorText = "Mandatory"; 
        MessageBox.Show("Error message"); 
    } 
    else 
    { 
        myGrid.Rows[e.RowIndex].Cells["MandatoryColumn"].ErrorText = string.Empty; 
    } 
} 
 
 更改是检查被验证的行是否脏 - 当您按下转义并删除一行时，它不再脏，所以这可以防止错误地尝试编辑它。 

This issue is explained in the following MSDN forums post: DataGridView + RowValidating = Index 4 does not have a value?
 
Basically it appears to be a bug (or at least very unexpected behaviour) in the way the DataGridView handles validation - the MessageBox.Show() causing validation on a row that no longer exists.
 
I found that the following change to your code fixes the issue:
 
private void myGrid_RowValidating(object sender, DataGridViewCellCancelEventArgs e) 
{ 
    // Note the check to see if the current row is dirty
    if (string.IsNullOrEmpty(myGrid.Rows[e.RowIndex].Cells["MandatoryColumn"].FormattedValue.ToString()) &&  myGrid.IsCurrentRowDirty) 
    { 
        e.Cancel = true; 
        myGrid.Rows[e.RowIndex].Cells["MandatoryColumn"].ErrorText = "Mandatory"; 
        MessageBox.Show("Error message"); 
    } 
    else 
    { 
        myGrid.Rows[e.RowIndex].Cells["MandatoryColumn"].ErrorText = string.Empty; 
    } 
} 
 
The change is to check that the row being validated is dirty - when you press escape and remove a row it is no longer dirty so this prevents incorrectly trying to edit it.