C# – How to format a column with number decimal with max and min in DataGridView

new DecimalFormat("#.##").format(1.199); //"1.2"

As pointed in the comments, this is not the right answer to the original question.
That said, it is a very useful way to format numbers without unnecessary trailing zeros.

You've added a button to your DataGridView and you want to run some code when it's clicked.
Easy peasy - just follow these steps:

Don'ts:

First, here's what NOT to do:

I would avoid the suggestions in some of the other answers here and even provided by the documentation at MSDN to hardcode the column index or column name in order to determine if a button was clicked. The click event registers for the entire grid, so somehow you need to determine that a button was clicked, but you should not do so by assuming that your button lives in a particular column name or index... there's an easier way...

Also, be careful which event you want to handle. Again, the documentation and many examples get this wrong. Most examples handle the CellClick event which will fire:

when any part of a cell is clicked.

...but will also fire whenever the row header is clicked. This necessitates adding extra code simply to determine if the e.RowIndex value is less than 0

Instead handle the CellContentClick which only occurs:

when the content within a cell is clicked

For whatever reason, the column header is also considered 'content' within a cell, so we'll still have to check for that below.

Dos:

So here's what you should do:

First, cast the sender to type DataGridView to expose it's internal properties at design time. You can modify the type on the parameter, but that can sometimes make adding or removing handlers tricky.

Next, to see if a button was clicked, just check to make sure that the column raising the event is of type DataGridViewButtonColumn. Because we already cast the sender to type DataGridView, we can get the Columns collection and select the current column using e.ColumnIndex. Then check if that object is of type DataGridViewButtonColumn.

Of course, if you need to distinguish between multiple buttons per grid, you can then select based on the column name or index, but that shouldn't be your first check. Always make sure a button was clicked first and then handle anything else appropriately. In most cases where you only have a single button per grid, you can jump right off to the races.

Putting it all together:

C#:

private void dataGridView1_CellContentClick(object sender, DataGridViewCellEventArgs e)
{
    var senderGrid = (DataGridView)sender;

    if (senderGrid.Columns[e.ColumnIndex] is DataGridViewButtonColumn &&
        e.RowIndex >= 0)
    {
        //TODO - Button Clicked - Execute Code Here
    }
}

VB:

Private Sub DataGridView1_CellContentClick(sender As System.Object, e As DataGridViewCellEventArgs) _
                                           Handles DataGridView1.CellContentClick
    Dim senderGrid = DirectCast(sender, DataGridView)

    If TypeOf senderGrid.Columns(e.ColumnIndex) Is DataGridViewButtonColumn AndAlso
       e.RowIndex >= 0 Then
        'TODO - Button Clicked - Execute Code Here
    End If

End Sub

Update 1 - Custom Event

If you wanted to have a little bit of fun, you can add your own event to be raised whenever a button is clicked on the DataGrid. You can't add it to the DataGrid itself, without getting messy with inheritance etc., but you can add a custom event to your form and fire it when appropriate. It's a little more code, but the upside is that you've separated out what you want to do when a button is clicked with how to determine if a button was clicked.

Just declare an event, raise it when appropriate, and handle it. It will look like this:

Event DataGridView1ButtonClick(sender As DataGridView, e As DataGridViewCellEventArgs)

Private Sub DataGridView1_CellContentClick(sender As System.Object, e As DataGridViewCellEventArgs) Handles DataGridView1.CellContentClick
    Dim senderGrid = DirectCast(sender, DataGridView)
    If TypeOf senderGrid.Columns(e.ColumnIndex) Is DataGridViewButtonColumn AndAlso e.RowIndex >= 0 Then
        RaiseEvent DataGridView1ButtonClick(senderGrid, e)
    End If
End Sub

Private Sub DataGridView1_ButtonClick(sender As DataGridView, e As DataGridViewCellEventArgs) Handles Me.DataGridView1ButtonClick
    'TODO - Button Clicked - Execute Code Here
End Sub

Update 2 - Extended Grid

What would be great is if we were working with a grid that just did these things for us. We could answer the initial question easily: you've added a button to your DataGridView and you want to run some code when it's clicked. Here's an approach that extends the DataGridView. It might not be worth the hassle of having to deliver a custom control with every library, but at least it maximally reuses the code used for determining if a button was clicked.

Just add this to your assembly:

Public Class DataGridViewExt : Inherits DataGridView

    Event CellButtonClick(sender As DataGridView, e As DataGridViewCellEventArgs)

    Private Sub CellContentClicked(sender As System.Object, e As DataGridViewCellEventArgs) Handles Me.CellContentClick
        If TypeOf Me.Columns(e.ColumnIndex) Is DataGridViewButtonColumn AndAlso e.RowIndex >= 0 Then
            RaiseEvent CellButtonClick(Me, e)
        End If
    End Sub

End Class

That's it. Never touch it again. Make sure your DataGrid is of type DataGridViewExt which should work exactly the same as a DataGridView. Except it will also raise an extra event that you can handle like this:

Private Sub DataGridView1_ButtonClick(sender As DataGridView, e As DataGridViewCellEventArgs) _
                                      Handles DataGridView1.CellButtonClick
    'TODO - Button Clicked - Execute Code Here
End Sub