How to stop two datagridview from using Unison Scrolling to independently using toggle button

Question

I have two datagridviews which have unison scrolling. now i want to use the button which will control unison scrolling and independently scrolling. My question is, how can i use toggle button to control unison and independently(which means it will be on and off).

I have created a button and named it Lock. let me put in a good scenario.

1.You will select one row from grid1 and perform unison scrolling.(Unison part is working) 2.And click Lock button which will allow unison scrolling. 3.Toggle the button off and it scrolls independently.

How can i do that ?

I have created this and it seems not working at all

Constructor of the form:

public frmMain_Page()
{
   Grid1.Scroll += new System.Windows.Forms.ScrollEventHandler(Grid1_Scroll);
}

Button for unison:

     private void Gridview_Input_Scroll(object sender, ScrollEventArgs e)
    {
      Gridview_Output.FirstDisplayedScrollingRowIndex = Gridview_Input.FirstDisplayedScrollingRowIndex;          
    }

Look button :

  private bool toggle = true;
  private void btnLock_Click(object sender, EventArgs args)
    {
        try
        {
            if (toggle == true)
            {
                toggle = false;
     Grid2.FirstDisplayedScrollingRowIndex =    Grid1.FirstDisplayedScrollingRowIndex;
            }
            else
            {
                toggle = true;
    Grid1.Scroll += new System.Windows.Forms.ScrollEventHandler(Grid1_Scroll);
            }
        }
        catch( Exception ex)
        {

        }

    }