Exporting a List of any type to Excel

A few months ago I posted a article about exporting and formatting a datagridview to Excel.

Well what about exporting a List<T> to Excel?
Sure, some may wonder but what's the point? Cause it's very easy to have
like a hidden dataGridView and when exporting one could easily add something like dvg1.DataSource = myList;. While it is totally true, it does have a downside in the memory consumption. Sure for small amounts of data no problem but for like 50.000 items each containg like 10-15 properties(e.g. 50.000 rows by 10-15 columns) the extra memory is not so ignorable. In winforms the dgv keeps a copy of the actual datas => twice needed memory. Firts for the List and again
for the dgv.

Ok so I'm too lazy to update the article so I decided to post a tip/trick.

OK so for a cell by cell aproach(SLOOOW) it will be something like:

//somewhere in the export methods
//create the column(s) header(s)
int col=1;
foreach(var propInfo in lst[0].GetType().GetProperties())
{
    //write down the property names => column(s) header(s)
    //lst a List<object>
    excelSheet.Cells[1, col] = propInfo.Name;      
    col++;
}

//put the actual datas
for (int i = 0; i < lst.Count; i++)
{
  int j = 1;
  foreach (var propInfo in lst[i].GetType().GetProperties())
  {
     excelSheet.Cells[i+2, j].Value = propInfo.GetValue(lst[i], null);
     j++;
  }
}

Here is the code from the article that does a fast export.
It creates a two dimensional object[,] from the datagridview.
Ideea "stolen" from Peter Moon.

//creates the two dimensional object[,] from the datagridview
private object[,] CreateTwoDimensionalObject()
{
    object[,] datas = new object[dgv.Rows.Count + 1, dgv.Rows[0].Cells.Count];

    //add the first row(the column headers) to the array
    for (int col = 0; col < dgv.Columns.Count; col++)
    {
        datas[0, col] = dgv.Columns[col].HeaderText;
    }

    //copy the actual datas
    for (int col = 0; col < dgv.Rows[0].Cells.Count; col++)
    {
        for (int row = 0; row < dgv.Rows.Count; row++)
        {
            datas[row + 1, col] = dgv.Rows[row].Cells[col].Value.ToString();
        }
    }

    return datas;
}

And Here is the method ported for a List<T>. List<object> actually:

//creates the two dimensional object[,] from the List
private object[,] CreateTwoDimensionalObject()
{
object[,] datas= new object[lst.Count + 1, lst[0].GetProperTies.Count]

int col=0;
foreach(var propInfo in lst[0].GetType().GetProperties())
{
    //write down the property names => column(s) header(s)
    //lst a List<object>
    datas[0, col] = propInfo.Name;
    col++;
}
//actual datas
for(int row=0; row<lst.Count; row++){
  int column = 0;
  foreach (var propInfo in lst[row].GetType().GetProperties()){
     datas[row+1, column] = propInfo.GetValue(lst[row], null);
     column++;
  }
}

Supose the method is named Export.
Now, to export a List<MyType> heres the needed code/trick:

List<object> lst = new List<object>
for(int i=0; i<5000; i++){
  MyType c = new MyType();
  c.Val = i;
  //add it to the list of objects
  lst.Add(c);
}

Now export it:

My.... .Export(lst);

Ahh... the VARIANCE... CO and CONTRA off course.