Accessing fields in a datatable

[maliary]

Hi, I have this code for looping through the fields in a data table and replace some characters in the fields. I am trying to access the fields in the datatable. Its giving this error : System.InvalidOperationException: Collection was modified; enumeration operation might not execute. Could you help me through this, I'd really appreciate it. foreach (DataRow dr in dtExport.Rows) { for (int i = 0; i < dtExport.Columns.Count; i++) { if (!Convert.IsDBNull(dr[i])) { data = dr[i].ToString(); data = data.Replace("\"", "\""); RowZ.Add(data.ToString()); } } dtExport.Rows.Add(RowZ.ToArray()); }

Let's do this !

modified on Thursday, August 14, 2008 10:27 AM

[Colin Angus Mackay]

You cannot add or remove elements in a collection (in this case dtExport) that you are iterating over.

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[Manas Bhardwaj]

Try using a for loop instead of for each. That should solve your problem

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[maliary]

This, which comes from a diffrent part of the code works

foreach (DataRow dr in TheDataTable.Rows)
{
for (int i = 0; i < iColCount; i++)
{
if (!Convert.IsDBNull(dr[i]))
{
string data = dr[i].ToString();
data = data.Replace("\"","\"");
sw.Write(data);
}
if (i < iColCount - 1)
{
sw.Write(separator);
}
}
sw.Write(sw.NewLine);
}

the diffrence with the other one is that, I want to put the elements back into a datatable, for other processing. I how do I make the change of the field values, then move the values into a data table again ?

Let's do this !

[maliary]

I changed it to this:

for (int j = 0; j < dtExport.Rows.Count; j++)
{

                for (int i = 0; i < dtExport.Columns.Count; i++)
                {
                    if (!Convert.IsDBNull(data = dtExport.Rows\[j\]\[i\].ToString()))
                    {
                        data = dtExport.Rows\[j\]\[i\].ToString();

                        data = data.Replace("\\"", "\\"");
                        RowZ.Add(data.ToString());
                    }

                }
dtExport.Rows.Add(RowZ.ToArray());

               
            }

but now I get this error System.ArgumentException:input array is longer than the number of columns in the table

Let's do this !

[Colin Angus Mackay]

I don't see any definition for RowZ, does it have more columns than the rows in the dtExport table?

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[maliary]

This is the definition, Arraylist Rowz = new Arraylist () Its an array list

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[Colin Angus Mackay]

Okay, I see. On the second loop you continue to add to the array RowZ, this means that it contains the column values for two rows by the time it gets to the dtExport.Rows.Add method. Since the array has more items in it than columns, the Add method fails as it doesn't know what to do with all that extra data. At the start of the loop over each row, you need to clear out the array.

RowZ.Clear();

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[acqy]

Do not put your updating statement within the foreach scope. Try use "for(int i=0;i

[maliary]

Hi, I have done that, and also placing the Row.Clear before the rows, but I still get the error: input array is longer than the number of columns in this table error ? Where should I have it ?

            for (int j = 0; j < dpExport.Rows.Count; j++)
            {
                 Row.Clear();

                for (int i = 0; i < dpExport.Columns.Count; i++)
                {
                    
                    if (!Convert.IsDBNull(dpExport.Rows\[j\]\[i\].ToString()))
                    {
                        
                        data = dpExport.Rows\[j\]\[i\].ToString();
                        data = data.Replace("\\"", "\\"");
                        Row.Add(data.ToString());
                    }

                }
                dtExport.Rows.Add(Row.ToArray());
            }

Let's do this !

[acqy]

OK, now it seems that we cannot update the dpExport within the loop. Try caching the rows to a local collection and after the loop update all the rows in the cache. I don't know if this helps.

Sunny Chen =============================================== System Analyst, System Architect Consultant of China System Analyst Institution
http://www.sunnychen.org ===============================================