DataGridViewColumn index gets changed after data clearing

Question

After filling DataSet, I insert two DataGridViewComboBoxColumns into some particular index:

dgvPayments.Columns.Insert(1, cmbPayMethod);
dgvPayments.Columns.Insert(3, cmbPayType);
dgvPayments.Columns.Insert(5, cmbMonth);

I have a cell click event in this DataGridView where I check against the index:

if (e.ColumnIndex == 6)
{
 ...
}

The first time I load the data the column index hits the correct column, but after clearing data the column index does not. What is wrong?

Answer 1

If your setup is thus:

1. In the form constructor, bind the DataGridView.DataSource to a collection.
2. In Form.Load, insert columns as you've shown in the OP.

3. "Clearing data" includes re-binding the DataSource.

   this.dataGridView.DataSource = emptyDataSource;
   

Then re-binding the DataSource essentially removes the sourced columns and readds them. This readjusts the manually inserted columns' indices to be the first ones - however it leaves the DisplayIndex untouched.

For example:

// DataSource added.
╔══════════════╦════════════╦════════════╦════════════╗
║              ║ "Source 1" ║ "Source 2" ║ "Source 3" ║
╠══════════════╬════════════╬════════════╬════════════╣
║ Index        ║     0      ║      1     ║      2     ║
║ DisplayIndex ║     0      ║      1     ║      2     ║
╚══════════════╩════════════╩════════════╩════════════╝

// Column inserted at index 1.
╔══════════════╦════════════╦════════════╦════════════╦════════════╗
║              ║ "Source 1" ║ "Insert 1" ║ "Source 2" ║ "Source 3" ║
╠══════════════╬════════════╬════════════╬════════════╬════════════╣
║ Index        ║     0      ║      1     ║      2     ║      3     ║
║ DisplayIndex ║     0      ║      1     ║      2     ║      3     ║
╚══════════════╩════════════╩════════════╩════════════╩════════════╝

// DataSource rebound.
╔══════════════╦════════════╦════════════╦════════════╦════════════╗
║              ║ "Source 1" ║ "Insert 1" ║ "Source 2" ║ "Source 3" ║
╠══════════════╬════════════╬════════════╬════════════╬════════════╣
║ Index        ║     1      ║      0     ║      2     ║      3     ║
║ DisplayIndex ║     0      ║      1     ║      2     ║      3     ║
╚══════════════╩════════════╩════════════╩════════════╩════════════╝

Solution:

Where you previously check for the index:

if (e.ColumnIndex == 1) // ==6 in your OP.

You could instead:

• Check that column's DisplayIndex:

  if (this.dataGridView.Columns[e.ColumnIndex].DisplayIndex == 1)
  

• Or, more preferably, check that column's Name:

  if (this.dataGridView.Columns[e.ColumnIndex].Name == "Insert 1")
  

Checking the Name is more reliable as it is less likely to change than the DisplayIndex and is more maintainable for future developers.