Question

每当我尝试从WPF Datagrid删除选定的行时，它都会正确删除该行，但是“ dataGrid1_SelectionChanged”事件引发一个异常，即对象引用未设置为对象实例。在删除行后，我无法处理这种情况。

private void dataGrid1_SelectionChanged(object sender, SelectionChangedEventArgs e)
    {

        OrignalSelectedRow = null;
        DataGrid gd = (DataGrid)sender;
       DataRowView rowSelected = dataGrid1.SelectedItem as DataRowView;

       int batchnumber = Convert.ToInt32(rowSelected["b_id"]); //This line is raising Exception
       //int batchnumber = batchidval;
       label16.Content = batchnumber;
    }

行删除代码在下面

 private void button6_Click(object sender, RoutedEventArgs e)
    {
        //Deletion of Row
        DataRowView rowSelected = dataGrid1.SelectedItem as DataRowView;
        int row_qty = Convert.ToInt32(rowSelected["qty"]);
        int row_batch_num = Convert.ToInt32(rowSelected["b_id"]);
        //label16.Content = row_batch_num;
        label16.Content = row_qty;
        con.Open();
        try
        {
            SqlCommand command = new SqlCommand("update batch set sold_qty=sold_qty-@qty2, left_qty=left_qty+@qty2 where id=@id2", con);
            command.Parameters.AddWithValue("@qty2", row_qty);
            command.Parameters.AddWithValue("@id2", row_batch_num);
            rexe = command.ExecuteNonQuery();
        }
        catch(Exception ex)
        {
            MessageBox.Show("Updation Error "+ex.ToString());
        }
        try
        {
            SqlCommand delcommand = new SqlCommand("DELETE FROM invoice WHERE sr#='" + rowSelected["sr#"] + "'", con);
            //con.Open();
            delcommand.ExecuteNonQuery();
            con.Close();

        }
        catch(Exception ex)
        {
            MessageBox.Show("Deletion Error " + ex.ToString());
        }
        if(rowSelected!=null)
        {
            dt_1.Rows.Remove(rowSelected.Row);   //dt_1 is a DataTable

        }
        dataGrid1.SelectedItem = 0;
    }

Answer 1

删除该行后，将没有选定的行。这意味着

DataRowView rowSelected = dataGrid1.SelectedItem as DataRowView;

是null，您无法访问它

rowSelected["b_id"]

一个简单的解决方案是检查null并在未选择任何行的情况下设置默认值：

DataRowView rowSelected = dataGrid1.SelectedItem as DataRowView;
if (rowSelected != null)
{
    int batchnumber = Convert.ToInt32(rowSelected["b_id"]);
    label16.Content = batchnumber;
}
else
{
    label16.Content = "No row selected";
}

更加紧凑：

if (dataGrid1.SelectedItem is DataRowView rowSelected)
{
    label16.Content = Convert.ToInt32(rowSelected["b_id"]);
}
else
{
    label16.Content = "No row selected";
}

从WPF DataGrid删除行后发生错误

1 个答案: